Flying faster because of decreasing winds

Guys,

flying the 737. On final approach you have at 2500ft AGL a wind ahead with for example 35kt. The wind at touchdown zone will be the same direction with only 10 kt. thats only an example. so many guys say you can fly a constant ground speed. but how? do i have to fly a faster indicated airspeed at the upper level?

Thanks for your help!

OD

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Olendirk

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15th November 2008, 09:20

  #2 (permalink)

electricdeathjet  Join Date: Jul 2007Location: ukAge: 32Posts: 85

Me thinks you are trying to copy the Airbus 'ground speed mini'

In a nut shell:

-Work out your g/s on touch down using tower wind and Vref.

-Then maintain the g/s during the approach (add on difference between tower wind and wind aloft to your normal Vref)..... Speeds may look strangely high but works nicely on the bus (automated).

** Be warned, you will not be stable at 500ft in most windy conditions**

Good Luck

 

15th November 2008, 09:49

  #3 (permalink)

BOAC Per Ardua ad Astraeus Join Date: Mar 2000Location: UKPosts: 9,068

Olendirk - you certainly keep on coming up with strange questions.

FORGET ground speed. On the 737 (all types) we fly IAS. Adjust power to maintain the correct/desired IAS with changing wind - it is not difficult and we have been doing it for over 100 years. No 'black magic computers', just basic flying skills. Quote:

so many guys say you can fly a constant ground speed. but how?

- ignore them - they are mad.

IF you choose to do it, the info is on your EFIS, but I suspect any Captain with half a brain would then take control and have you sectioned - I would.

ERADICATE Airbus from your vocabulary until you need to speak it.

 

15th November 2008, 11:31

  #4 (permalink)

Nightrider  Join Date: Sep 2003Location: last week I was in....now, where am I now?Posts: 145

Yes, yes and yes.

No G/S during approach! Fly IAS as calculated!

 

15th November 2008, 16:53

  #5 (permalink)

Chris Scott  Join Date: Jan 2008Location: England (N. Downs)Age: 62Posts: 387

BOAC,

That was an uncharacteristically tetchy and provocative response to a fair question.

And, in your case, unexpectedly ill-informed.

We have all been taught to fly approaches purely on IAS in the way you describe, and many of us have used the technique on a variety of jet aircraft. It is well known, however, that a 25-knot headwind at 100ft can disappear to nothing at the threshold, particularly at night and/or when the airfield is surrounded by trees. Unlike most propeller aeroplanes, increasing the power on a jet does not in itself generate extra lift from the wing; it may provide a small vertical component of thrust. And jet-engine response is slower than pistons and turbo-props.

Airbus, for all its virtues, did not invent the concept of calculating a minimum acceptable GS on finals – they merely introduced it to line pilots in automated form on the A320 in 1988. With the advent of INS in the 1970s, giving a reliable (unlike Doppler in the 1960s) and fairly accurate GS at all speeds, the concept was soon pioneered by crews. It was first explained to me by a flight engineer on the DC10, and I wouldn't be surprised if it was an American idea. Perhaps someone will enlighten us.

The popular us-and-them attitude between Boeing and Airbus pilots is ill-considered. Both manufacturers

produce conventional aeroplanes with minor differences. All their products are well-built and fly well, using similar aerodynamics.

You know only too well that aeroplanes have to operate within the laws of Newtonian physics, one of which involves inertia. Inertia is a function of GS, not IAS. But lift requires IAS. As every schoolboy knows: IAS = GS plus headwind-component (sea-level/ISA). Shortage of inertia (GS) can only be corrected by applying extra thrust; for a period of time. On a bad day at the office, that time may not be available.

I would be very surprised if no Boeing pilot on this forum has ever applied the principle of working out a minimum acceptable ground-speed. You might even consider it yourself.

Chris

Last edited by Chris Scott : 17th November 2008 at 02:45. Reason: No changes since John Tullamarine's. In the penultimate paragraph, readers are warned that I loosely used the word "inertia" to mean "kinetic energy". See post #22.

 

15th November 2008, 19:02

  #6 (permalink)

BOAC Per Ardua ad Astraeus Join Date: Mar 2000Location: UKPosts: 9,068

Quote:

I would be very surprised if no Boeing pilot on this forum has ever applied the principle of working out a minimum acceptable ground-speed. You might even consider it yourself.

- I would not and NO!

I must admit that I stall at an IAS and not a G/S, old-fashioned as that may be.

PS No 'us and them' - merely sound advice to a 737 pilot. Of course, if olendirk's airline starts teaching G/S approaches, wipe all of that.

 

15th November 2008, 19:22

  #7 (permalink)

Wizofoz  Join Date: Jun 2001Location: Second Camel on the left....Posts: 1,884

Quote:

Inertia is a function of GS,

Whilst it doesn't alter the thrust of your post, that isn't strictly(or to be more precise, necessarily) true.

Inertia, also known as momentum, is Mass * Velocity. Velocity, however, is relative to whatever frame of reference you choose. A body has a certain velocity reference the ground, therefore a certain momentum

relative to the ground, but messuring it's velocity reference the air around it is just as correct.

Newtons (and Einsteins) laws are Universal. They don't somehow only apply to movement relative to out very small Earth.

 

15th November 2008, 20:02

  #8 (permalink)

bookworm  Join Date: Aug 2000Location: UKPosts: 2,597

Quote:

A body has a certain velocity reference the ground, therefore a certain momentum relative to the ground, but messuring it's velocity reference the air around it is just as correct.

Only if that air is not accelerating relative to an inertial frame. Because air is itself dynamic, that is not generally the case. In windshear your airspeed changes instantaneously, your groundspeed cannot.

 

15th November 2008, 20:05

  #9 (permalink)

Wizofoz  Join Date: Jun 2001Location: Second Camel on the left....Posts: 1,884

True enough, bookworm, and that is why windshear is an issue, though whether it is the air or the aircraft that is changing velocity is ALSO a matter of what frame of reference you are using.

The misconception, however, that velocity is mesurable only reference the earths surface is what leads to faulty concepts like the infamous "downwind turn" myth.

 

15th November 2008, 20:40

  #10 (permalink)

bookworm  Join Date: Aug 2000Location: UKPosts: 2,597

Quote:

True enough, bookworm, and that is why windshear is an issue, though whether it is the air or the aircraft that is changing velocity is ALSO a matter of what frame of reference you are using.

But momentum is not conserved in non-inertial frames. Thus the frame of the air is about as much use as a chocolate teapot when it comes to working out why your aircraft is sinking into the weeds because you failed to take account of the 30 knot drop in headwind in planning your approach! Minimum groundspeed looks very sensible to me.

Quote:

The misconception, however, that velocity is

mesurable only reference the earths surface is what leads to faulty concepts like the infamous "downwind turn" myth.

I don't agree with that. It's perfectly possible to debunk "the infamous downwind turn myth" in any inertial frame -- you just have to remember that velocity, and therefore momentum, is a vector not a scalar.

 

15th November 2008, 20:51

  #11 (permalink)

Wizofoz  Join Date: Jun 2001Location: Second Camel on the left....Posts: 1,884

Booky,

I concede both points.

In the first, I was only speaking about the entirerly hypothetical. GS v IAS is indeed a sensible measue of the effects of windshear.

In the second, certainly true and I have done just that, but the initial misconception usually comes from people saying that momentum is speed (scalar) over the ground times weight, when velocity (vector and reference ANYTHING) times mass in in fact the case.

 

15th November 2008, 20:55

  #12 (permalink)

bookworm  Join Date: Aug 2000Location: UKPosts: 2,597

Quote:

I concede both points.

Damn it Wiz, so what am I going to do with the rest of my Saturday evening if I can't even pick an argument on Tech Log?

 

15th November 2008, 21:11

  #13 (permalink)

Wizofoz  Join Date: Jun 2001Location: Second Camel on the left....Posts: 1,884

Hmmm,

OK, try this one:-

They shouldn't call it a stall turn, because the aircraft never stalls.....

 

15th November 2008, 21:23

  #14 (permalink)

Loose rivets Psychophysiological entity Join Date: Jun 2001

Strange. When I started to write this, I was convinced that getting a groundspeed as an actual figure, was a total waste of time. By the time I had made my comment, I wasn't so sure. It went something like this.

Location: Texas or Essex or London or....Age: 69Posts: 1,428

Hah! I thought I was the one that always wanted to analyze things down to relativistic accuracy. But in this case, it seems that we've always had that ground speed thing ticking away in the back of our minds anyway.

Knowing the 2000' winds and surface winds, we then only have to factor in gusts. Doesn't that cover everything that's being said? This is assuming of course we're flying the correct range of IASs.

We get back to that 'It looks wrong' issue if the ground speed seems visually low. Just sitting here in my dotage, I get an very uncomfortable feeling when I visualize a surface-wind-induced crawl over the last half mile before touchdown. It just smells dangerous, but I could never imagine wanting to know my groundspeed in kts.

Okay, now we're in a modern electronic flight deck that might be landing in CAT several. Getting groundspeed is a touch of a button. Maybe, if the PF can get the feel from that figure that I used to get from the visual image, then that could only be to the good. I would suggest however, that the full meaning of that visual image should be well ingrained first.

But as for flying a groundspeed per se, that's just lost on me.

 

15th November 2008, 21:35

  #15 (permalink)

Port Strobe  Join Date: Jun 2003Location: GlasgowPosts: 164

Quote:

Inertia is a function of GS

Horlicks.

To stay on topic Boeing didn't offer GS mini as an option and still don't to this day afaik, nor would airmanship suggest you try to imitate it, hence why deviate from what FCTM tells you to do with the command speed? They probably know best, when you get a bus job then let autothrust faff with your speed until you're content.

 

16th November 2008, 20:52

  #16 (permalink)

Chris Scott  Join Date: Jan 2008Location: England (N.

Wizofoz,I see that you are a purist, like me. As you say, no velocity is absolute; it has to be relative to something. However, astronauts excepted, pilots and humans

Downs)Age: 62Posts: 387

usually measure it in relation to the local surface of mother earth. Although the latter is revolving at up to 900kt about the Earth's axis, and the Earth is making its rapid journey around our sun, and our sun is travelling around the Milky Way galaxy, etc.; this reference is steady enough – and therefore useful – for the purpose of defining the "V" in the kinetic-energy equation.The same cannot be said for the atmosphere, I can assure you, particularly when you are descending through divers layers of same.

Port Strobe,If it's "Horlicks" to state that, for a given mass, inertia (kinetic energy) is a function of GS, perhaps you can tell us what else? IAS?Although I was trying to avoid formulae, it is actually proportional to the GS (velocity) squared, which makes a shortage of it even more difficult to correct.You also suggest: "...when you get a bus job then let autothrust faff with your speed until you're content."A/Thr is not required, unless demanded by an airline's SOP. During 14 years on the A320, 90% of my manual approaches were flown with manual thrust from 1000ft, and 99% with "managed" IAS indicated as the target speed on the ASI. "Managed" IAS always provides GS-mini protection on Airbuses since the A320.The great thing is: you don't need so many thrust changes – see (4), below.

BOAC,

(1) We agree on one point: adherence to SOPs. That was the only post-posting misgiving I had yesterday evening. See (5), below.

(2) But you are still choosing to misinterpret the concept of avoiding an unsustainably low ground speed on the approach. Perhaps you should read my post again – more carefully. And electricdeathjet's.Given the chance, of course, Airbuses would stall in exactly the same way: at an IAS. The trick on the approach is to avoid a predictable, critical loss of IAS by anticipating the loss of headwind.Let's look at the common example in my post above. Using your traditional technique: if the surface wind is known to be calm, you will have added nothing to your approach IAS. Assuming sea-level/ISA, an approach speed (VAPP) of 125kts, and a steady headwind of 25kts above (say) 100ft; you will be soldiering on in your B737 quite happily at a GS of 100kts. Fine so far... But what is the point, when you know that your GS is going to need to increase by 25kt in the last 100ft (10-12 seconds) of the approach; involving a big handful of thrust, and (not being an A320) a lot of pushing/re-trimming?

If the SOP is to fly a stabilised approach, why allow it to be predictably de-stabilised close to the ground?

(3) You imply that we are ignoring the all-importance of IAS. On the contrary: IAS is precisely what we are trying to conserve.

(4) The "GS-mini" concept protects IAS by constantly offering the pilot an IAS target ("managed speed") which results from: the higher of VAPP and the IAS required to achieve the minimum GS.If the headwind component on the approach is higher than reported on the ground (and entered into the PERF page of the FMGS), the IAS target will be above VAPP. It will also rise and fall with the current headwind component. Despite (in fact, because of) this changing IAS target, the thrust requirement remains roughly the same, because the aircraft's kinetic energy remains constant at the constant GS.

(5) This changing, managed IAS produces two issues that have to be addressed. > (a) SOP stabilised-approach IAS criteria have to be relaxed slightly. In the above example, the managed IAS target at 500ft would be VAPP+25 (150kt).> (b) If the difference between headwinds aloft and on the ground is very great – say, 45kt at 1500ft – the resulting IAS target of VAPP+45 may exceed the flap limit for the next flap extension. So a suitable selected IAS has to be maintained, which will often be dictated by ATC anyway. As the headwind declines, the GS rises, and managed IAS can be introduced, subject to ATC.

 

16th November 2008, 21:05

  #17 (permalink)

Chris Scott  Join Date: Jan 2008Location: England (N. Downs)Age: 62Posts: 387

D.I.Y. GS-mini?

So what about you, Olendirk, trying to stay within SOPs in your Boeing 737; next to a captain like BOAC, wielding his rolled-up newspaper – ready to flagellate?

I presume you are flying an approach speed which has been calculated by yourself – or by the FMS, based on the reported surface wind; and that you are using an IAS knob manually to alter the target? If that surface wind is small, you will have added little to VREF, and are at the most vulnerable to the inevitable wind-sheer. With luck, the sheer will be gradual – but it may be sudden, as in my example (see my previous posts).

To deal with serious cases, my suggested technique starts with calculating an estimated threshold GS. This involves correcting threshold IAS to TAS, if necessary; then subtracting the headwind component. This is

"GS-mini". Once established in landing config at the selected approach IAS, look at the indicated GS. If it is below GS-mini, wind up the selected IAS to try and correct it, but do not exceed the stabilised-approach IAS criterion for this approach. Do not exceed GS-mini. As the headwind falls, GS rises, so you must reduce the selected IAS. Once it has reached the original approach speed, leave it alone.

Ensure you NEVER select an IAS below the SOP approach speed. If the tower reports a big revision to the reported surface wind, revert to the normal SOP (and, just as normal, consider the possibility of a go-around). In any case, ensure that the calculated approach speed is selected by 100ft. [Once the AP has been disconnected, these selections have to be made by the PNF.]

If the above technique is unacceptable to your fleet managers and trainers, or to the captains you fly with, there may be very good reasons; the possibility of mis-selecting too low an IAS being one, depending on your FCU and FMS. BOAC's opposition may seem to be pure Luddism, but it could also be that he is in the honourable business of enforcing SOPs. In less-regulated times, it has been done on other aircraft. You, however, may have to wait for an Airbus...

 

16th November 2008, 22:38

  #18 (permalink)

SR71

Mach 3 Join Date: Aug 1998Location: StratospherePosts: 397

Just being a pedant, but inertia is not the same as kinetic energy.

The only thing its proportional to is mass.

 

17th November 2008, 00:29

  #19 (permalink)

Port Strobe  Join Date: Jun 2003Location: GlasgowPosts: 164

Quote:

If it's "Horlicks" to state that, for a given mass, inertia (kinetic energy) is a function of GS, perhaps you can tell us what else? IAS?Although I was trying to avoid formulae, it is actually proportional to the GS (velocity) squared, which makes a shortage of it even more difficult to correct

Mass is a measure of inertia, not groundspeed, indicated airspeed or any other flavour of speed. To say a helicopter in the hover has no inertia is simply inaccurate, not pedantic as SR71 suggests. Momentum is a function of groundspeed (taking an Earth fixed frame of reference as absolute for our purposes) for a

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given mass, not to be confused with inertia. I don't require the Ladybird guide to kinetic energy either thanks.

On the subject of being accurate I was incorrect to suggest GS mini is controlled by autothrust, so let managed speed faff with the command speed until you're content then.

The postings this evening seem to be a sales pitch for the Airbus. It may be a clever machine but I'm not qualified to give backing nor counter arguement to your statements. I am qualified to say faffing with the command speed on the Boeing is not the way they nor the vast majority of operators propose to use the AFDS. To think you're smarter than them and the person three feet away by doing so is a shortcut to creating an incident in my own opinion. On the assumption we're talking about relatively modern passenger jets then the instant wind is going to be right under your nose so any drop in airspeed can be anticipated, it's basic situational awareness. Manipulating the thrust and flight controls is part of a pilot's job description so I don't object to having to do that. If the windshear is going to be really sudden then it calls into question whether or not you should be executing an approach in the first place, plus you'll probably get a predictive if not reactive windshear warning. Horses for courses, but transferring techniques between types simply doesn't seem sensible to me.

Last edited by Port Strobe : 17th November 2008 at 00:39.

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17th November 2008, 00:39   #20 (permalink)

john_tullamarine Moderator Join Date: Apr 2001Location: various places .....Posts: 3,086

I'm just a dinosaur but, for what it might be worth -

(a) is not the Airbus technique similar in intent to the Boeing approach additives ?

(b) where we are looking at the potential for windshear, my observation has been that the majority of pilots will carry extra speed if the circuit wind is moderately different to that on the surface .. neither Boeing nor Airbus can read the real wind profile .. and the pilot retains the option of the miss if it turns out to be unmanageable.

The worry I see is the pilot who rigidly sticks to whatever protocol without thinking about

what he/she is doing... as a wise checkie put it to me years ago .. "Lad, the Ops Manual should have a sentence on the preface sheet saying something like ..'to be read with an bit of commonsense ..' "

Quote:

Lad, the Ops Manual should have a sentence on the preface sheet saying something like ..'to be read with an bit of commonsense ..

I absolutely 100% agree. What ought to be understood is the spirit of the rules, and what I'm getting at is creeping back the command speed is not an underlying principle Boeing wish to promulgate, so don't do it on a Boeing for common sense doesn't suggest you do so. I wouldn't rigidly stick to the manuals at the expense of operational advantage let alone safety, but I think I've said enough times my point is Airbus speed control techniques on the Boeing aren't the way forward when the minimum crew is two and half of them probably aren't educated in the technique.

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17th November 2008, 01:51   #22 (permalink)

Chris Scott  Join Date: Jan 2008Location: England (N. Downs)Age: 62Posts: 387

SR71,

You're not being a pedant at all, and I'm beginning to regret ever using the word inertia; although my dictionary [Collins] defines it as: "the tendency of matter to remain at rest (or to keep moving in the same direction) unless affected by an outside force", which is precisely what I'm talking about.

However, my old Physics book [A.R.W.Hayes] says: "Inertia or mass... is the property by which it tends to resist changes in motion. Numerically it is the constant M..." So inertia is mass, as you say: independent of velocity.

By the way, it defines momentum as "...the product of its mass and its velocity", (i.e., Momentum=Mv, where M is mass and v is velocity). It also says: "Momentum should not be confused with kinetic energy. Momentum is indestructible. Unlike kinetic energy, it cannot be converted to some other form." Kinetic energy (they refer to it as "translational kinetic energy") is defined as the familiar ½ Mv².

So you are right: I should have been more careful about the use of the word "inertia"; and not suggested it was the same thing as kinetic energy.

Am tempted to edit my posts; but that would be cheating, and I don't think the error will have misled anyone in this empirical context. Serious readers will see this, and to them I offer my apologies.

Chris

 

17th November 2008, 03:05

  #23 (permalink)

Chris Scott  Join Date: Jan 2008Location: England (N. Downs)Age: 62Posts: 387

Quote from Port Strobe:The postings this evening seem to be a sales pitch for the Airbus.[Unquote]In my first post, I pointed out that the concept of a minimum acceptable ground speed was not invented by Airbus, as far as I know. If by explaining roughly how their GS-mini works – in the face of familiar anti-Airbus sentiment from one or two Boeing advocates – I have shown Airbuses in a favourable light, so be it.

Quote from Port Strobe:...so let managed speed faff with the command speed until you're content then.[Unquote]See what I mean?

Quote from Port Strobe:Horses for courses, but transferring techniques between types simply doesn't seem sensible to me.[Unquote]I agree as a general rule. Hence the several caveats to Olendirk in my post #17. But john tullamarine suggests: "where we are looking at the potential for windshear, my observation has been that the majority of pilots will carry extra speed if the circuit wind is moderately different to that on the surface."

Does Boeing issue specific advice on this? Olendirk would like to know.

Merely to say, as Port Strobe does, that "any drop in airspeed can be anticipated, it's basic situational awareness", does not do justice to the argument.

 

17th November 2008, 05:10

  #24 (permalink)

galaxy flyer  Join Date: Dec 2002Location: Quabog Valley, USAAge: 56Posts: 875

To Chris Scott's question:

I don't know if we invented "managed IAS", but the USAF uses something like this on its heavy transports. Originally, it was computed by the flight engineer, using approach TAS adjusted with current tower winds to calculate a "reference GS", the pilots then added enough knots to fly the plane at a groundspeed that

was equal to the "reference GS". Later, it was automated thru the FMSs which did the calculated and displayed the "reference GS" and produced an aural warning, if the actual GS was less than reference GS.

It came out of windshear accidents and the ability of INS systems to show real time ground speeds. I thought it was useful for aircraft which have high momentums and low excess power-the C-5, for example. That said, we still had prohibitions about operations in windshear and TRW conditions.

GF

 

17th November 2008, 05:28

  #25 (permalink)

Wizofoz  Join Date: Jun 2001Location: Second Camel on the left....Posts: 1,884

Chris,

Whilst an aircraft is in flight, it's inertia, momentum, kinetic energy or anything else can be measured with respect the the earth, the moon or alpha-centauri and it doesn't make the blindest bit of difference to the aircraft.

A Tiger Moth with a TAS of 70kt, flying into a 70Kt headwind has, according to you, no kinetic energy, yet will fly along (well, it's not actually GOING anywhere!) just fine. The aircraft flys due to the air flowing over it's surfaces. How fast that moves it WRT the earths surface has no bearing on it's performance.

The only relevance ground speed has is that we often have a read-out of it if we have INS or GPS aboard, and the difference between that and our TAS is the wind. Changes in that relationship indicate changes in the wind, which IS relevant as that is the air we are flying through. But GS in isolation (and therefore Momentum, Kv or anything else reference the earths surface) has no bearing on the aircraft at all.

 

17th November 2008, 11:09

  #26 (permalink)

Chris Scott  Join Date: Jan 2008Location: England (N. Downs)Age: 62Posts: 387

Hi Wizofoz,

I agree with your first two paragraphs, but disagree with the implications contained in your final one.

You are making light of the fact that, if the 70-knot headwind suddenly dies away, the inertia of your Tiger Moth (aaah, De Havilland!) will have to be overcome in order to increase its GS from zero to whatever it needs to restore a flyable IAS. If to do this it needs to regain its original TAS of 70kt, it will need to accelerate to a GS of 70kt.

If GS has to be changed, so must be the kinetic energy, which is also a vector and therefore relative to a datum (we normally use the earth's surface but, as you say, it could be anything). Increasing the kinetic energy involves the application of power for a period of time. [I'm aware that, in purist terms, "kinetic energy" is more of a concept than a reality; but it's one that works quite well enough for the purpose of this discussion.]

If your Tiger Moth was achieving a TAS of 70kt into a 140-kt headwind, its GS would be minus-70kt. If the wind suddenly dropped to 70kt, the Tiger would need to increase its GS from minus-70kt to zero. That would require a similar amount of [power x time] as in the first case. Power x time = energy. So the Tiger needs to increase its "kinetic energy".

Now: are you a bit happier?

 

17th November 2008, 11:27

  #27 (permalink)

VinRouge  Join Date: Jul 2007Location: GermanyPosts: 295

Just to note, I have seen a 50Kt drop off in about 50 Ft above touchdown, in the desert. (Desert Night time Jets). TIs a pretty hideous situation as you have to add a fair whack of power before you enter it. The clue is in the tower reporting winds calm whilst the air you are flying in is moving at 70 Kts on the nose!

can also get interesting if it is a tailwind component. Especially flying a jet without brakes.

 

17th November 2008, 12:14

  #28 (permalink)

SR71

Mach 3 Join Date: Aug 1998Location: StratospherePosts: 397

Quote:

...kinetic energy, which is also a vector...

No, its not.

This is great fun....

 

17th November 2008, 12:36

  #29 (permalink)

Wizofoz  Join Date: Jun 2001Location: Second Camel on the left....Posts: 1,884

Chris,

The amount which an aircraft needs to accelerate due to a change in the wind in order to regain it's original airspeed is equal to the change in the wind. All frames of reference relevant to the flight of the aircraft are to

do with the air it's flying through. As a consequence, yes it's velocity relative to the ground will change, and as such all consequential values which have velocity as a factor will change relative to the surface, but that is consequential, not causational.

Lets suppose that while the aircraft is in flight, someone attaches a mega rocket to the earth and suddenly changes it's rotational speed. Let's, for argument, assume friction doesn't cause the atmosphere to change IT's velocity, so the aircraft is still flying in the same surrounding air. The aircraft now has a ground speed that might be greater, less or sideways!! Relative to an observer on the ground, it's ground speed, momentum and Kv will all have changed. Will it effect the way the aircraft flys? Not at all! The aircraft won't know, until such time as it tries to land on the earths surface.

Perhaps the concept you are not quite seeing is the amount of kinetic energy an object has is relative to the observer.

 

17th November 2008, 13:50

  #30 (permalink)

Capt Groper  Join Date: Oct 1998Location: OSAge: 50Posts: 39

Higher IAS in headwinds / WS

I'm flying with Chris Scott, his approach is sensable.

BOAC, like the name, is old hat.

GS Mini works well and avoids unnessary THR changes, either automatixc or manual.

Plus you have energy available to overcome that last minute sinking feeling with rapid IAS decrease.

Good points from John_tullamarine(a) is not the Airbus technique similar in intent to the Boeing approach additives ?

ATC like the higher GS, keeps the traffic flow optimal.

Anyway great discussion topic.

 

17th November 2008, 14:01

  #31 (permalink)

BOAC Per Ardua ad Astraeus Join Date: Mar 2000Location: UKPosts: 9,068

Hello cpt G - thank you for your deference to my age.

I should, however, point out that the 'advice' to Olendirk is anything but 'old hat' but it right 'up to the minute' CORRECT a/c handling technique - for 737, that is, not Tiger Moth or Airbus, which is what was asked.

Regarding your last 2 points:

No they don't when they have asked for an airspeed, and it could completely scupper the plan causing a g/a for you or cancellation of a departure ahead .

Yes it is

 

17th November 2008, 15:41

  #32 (permalink)

SR71

Mach 3 Join Date: Aug 1998Location: StratospherePosts: 397

I'm not sure what a Quote:

unsustainably low ground speed on the approach

is, but is it slower than this:

YouTube - STOL - Short Take Off and Landing

 

17th November 2008, 17:53

  #33 (permalink)

Chris Scott  Join Date: Jan 2008Location: England (N. Downs)Age: 62Posts: 387

Hi again, SR71,

Your minimalist and unhelpful interjections have certainly made me dust off my A-Level (1960s) Dynamics, which has been rewarding, and for which I'm most grateful. It has indeed been fun, but I suspect we are now at risk of getting a little more off topic than is really productive?

When I bravely stated that "kinetic energy" is a vector, I was thinking of the Tiger Moth with its TAS of 70kt into a headwind of 140 (see post #26). Its GS, in pilot terms, is minus 70, because aeroplane pilots think of GS in the direction of intended travel; i.e., "Track" (loosely speaking, forwards). The same must therefore apply, by definition, to its "kinetic energy"?

To illustrate my point, remember my example: when the headwind suddenly dropped to 70kt, the Tiger had to accelerate its GS from -70kt to 0kt to restore its TAS/IAS. This required an energy input to overcome its inertia (mass), i.e., its "kinetic energy" had to be increased from the point of view of the pilot.

But from the point of view of someone standing far below on the ground, who may not have been able to see which way the Tiger was trying to go, it actually appeared to decelerate from 70kt to 0kt (stationary). This implies a decrease in kinetic energy. So the extra power (or thrust, if you want to achieve the same result by a slightly different method) has, from this point of view, been negative.

Anyone confused yet? Kinetic energy, as I think Wizofoz may be already reminding me – like GS (velocity) – is purely relative to the observer. But, additionally, the direction in which it is acting is all-important. A speed is a speed (relative to a point); but a velocity is a speed and a direction/bearing (relative to a point). Similarly, the concept of kinetic energy can only be meaningful if its direction is specified. If that does not make it a vector, then please let me know what I can call it, and I'll oblige.

Quote from Wizofoz:The amount which an aircraft needs to accelerate due to a change in the wind in order to regain it's original airspeed is equal to the change in the wind. All frames of reference relevant to the flight of the aircraft are to do with the air it's flying through.[Unquote]

Yes, but let me remind you that the concept of wind is equally relative; it is universally defined as a velocity relative to the earth's surface. The problem for pilots arises when it changes, not when it is steady.

That's what the concept of a minimum acceptable GS on the approach is all about. Can we get back to the subject, please?

 

17th November 2008, 18:48

  #34 (permalink)

bookworm  Join Date: Aug 2000Location: UKPosts: 2,597

Quote:

When I bravely stated that "kinetic energy" is a vector,

If you substitute the word "momentum" for "kinetic energy" in the above, you'd be correct.

 

17th November 2008, 19:23

  #35 (permalink)

Wizofoz  Join Date: Jun 2001Location: Second Camel on the left....Posts: 1,884

Quote:

The problem for pilots arises when it changes, not when it is steady

The problem arises when it changes relative to the aircraft. What it is doing relative to the earths surface has no bearing on the aircraft. One way of detecting the fact that it is changing is the reationship between airspeed and groundspeed, but, answer me this, could you safely do an approach based on groundspeed only, with no reference to airspeed and therefore no knowledge of the winds velocity?

 

17th November 2008, 20:48

  #36 (permalink)

SR71

Mach 3 Join Date: Aug 1998Location: StratospherePosts: 397

Quote:

Similarly, the concept of kinetic energy can only be meaningful if its direction is specified. If that does not make it a vector, then please let me know what I can call it, and I'll oblige.

Absolutely not.

A vector by definition is that which has both a magnitude and a direction.

A scalar by definition is that which has only a magnitude.

Kinetic energy is a scalar because the V^2 in the definition thereof is defined as the scalar product of the velocity with itself i.e., V.V, and is a scalar.

Kinetic energy is the energy an object possesses by virtue of its motion.

Or alternatively, the change in kinetic energy of an object is equal to the work done by a conservative force.

So kinetic energy and work must have the same units and type.

Work is the scalar product of force and displacement.

Force and displacement are vectors, and the scalar product of two vectors is a scalar.

But I'm confused...

The aircraft knows nothing about what the earth below it is doing. It doesn't need to, as Wizofoz suggests.

Whether it touches down at a GS of 0kts or 70kts, as long as the IAS/TAS is the appropriate one, what is the problem?

I've touched down in a light 737 at a GS of <90kts on a day when it was gusting 65kts. I didn't even think about GS. The only thing I seek to preserve on finals is IAS. If I fly through a shear, I need to regain IAS surely, not GS?

What am I missing?

 

17th November 2008, 21:54

  #37 (permalink)

framer  

I'm surprised that nobody has mentioned this. Qantas boeing crew use RGS or reference ground speed. It

Join Date: Sep 2008Location: sydneyAge: 41Posts: 180

basically provides them with a ground speed they don't go below. Works well. Has anyone corrected this yet?.... Quote:

Inertia, also known as momentum, is Mass * Velocity.

Come on Wiz....inertia has nout to do with velocity, you know that! It stays the same regardless of velocity.

 

18th November 2008, 02:01

  #38 (permalink)

autoflight  Join Date: Jun 1999Location: Brisbane, AustraliaPosts: 127

I am extremely surprised and disappointed that there are so many who cannot accept the part that G/S mini has to play during windshear.

 

18th November 2008, 02:30

  #39 (permalink)

Mark1234  Join Date: May 2006Location: Melbourne, AUSPosts: 290

Quote:

Originally Posted by SR71 I've touched down in a light 737 at a GS of <90kts on a day when it was gusting 65kts. I didn't even think about GS. The only thing I seek to preserve on finals is IAS. If I fly through a shear, I need to regain IAS surely, not GS?

Been following the thread with interest, and I think this is the crux of it. Having a minimum GS serves to protect the IAS. BUT that's not the only way of doing it.

<disclaimer> I'm just an interested PPL, with aspirations to bigger tin..</disclaimer>

Starting assumption is that a large transport category aircraft has significant inertia (resistance to change), so if the 65kt headwind suddenly disappears, it's going to be a big issue accelerating the aeroplane. If it happens at just the wrong moment we might finish up with upset passengers, and possible landing gear protruding from places it shouldn't: We all know that IAS makes it fly, however, we have some need to protect the IAS.

If we implement a minimum GS <airbus>, we protect the IAS because even if the wind should spontaneously reduce to zero, we're still rocking along fast enough to fly - the IAS will take a dive, but it will take a dive from a higher point to a point at which the plane still flies.

In the event that there is no shear, and we fly through a continuously decreasing headwind, the IAS will

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slowly wind down to some target value, at which point the IAS will stop decreasing, and GS will start to increase (it's GS mini, not target GS). In the event the headwind remains, we will arrive at a higher IAS AND GS than might be necessary.. but it's still not an excessive GS (perhaps somewhere around a 0 headwind GS), so shouldn't be a problem.

If we don't reference GS <boeing> then given the reported conditions, and experience, then I presume we (the pilot) takes some action to protect the IAS by adding some knots for headwind/gust factor?

Which surely amounts to about the same thing (protecting the IAS), just by different routes?

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18th November 2008, 08:19   #40 (permalink)

Anp  Join Date: Dec 2003Location: S/SEPosts: 7

Having read the thread being discussed by stalwarts, it finally required someone with less experience like Mark1234 to put thing simply so that there is no more confusing GS Mini with KE, inertia, momentum etc…. Energy level required to see you through a sudden loss of head wind component close to the ground is what the GS Mini provides. In other than the Airbus we come in with an additive factor (as John put it) which is a rough figure mentally calculated by the pilot (or the flt engineer if you have the luxury of having one). The GS Mini removes this mental maths and lets the pilot concentrate on the approa

Quote:

Which surely amounts to about the same thing (protecting the IAS), just by different routes?

The OP wanted to fly the Airbus paradigm in his Boeing.

The Boeing proponents said, "Why?"

The Airbus proponent(s) said "Because its better. You protect IAS by flying a mini GS. You don't have de-stabilising thrust inputs late in approach."

(Not that I fly the Airbus, but are Airbus pilots and their machine so cool as to not bother to add thrust even if they did fly through a shear?)

The Boeing proponents said "We protect IAS by protecting IAS. Whats the big deal?" (Not many of us still here can say it hasn't worked for us...even BOAC, and by anecdotal accounts, he has been around a while.)

And then everybody got confused...

As for removing the mental maths, thats mental.

 

19th November 2008, 02:01   #42 (permalink)

Chris Scott  Join Date: Jan 2008Location: England (N. Downs)Age: 62Posts: 387

Excellent one, Mark1234! All correct.

Quote from galaxy flyer:I don't know if we invented "managed IAS", but the USAF uses something like this on its heavy transports. Originally, it was computed by the flight engineer, using approach TAS adjusted with current tower winds to calculate a "reference GS", the pilots then added enough knots to fly the plane at a groundspeed that was equal to the "reference GS". Later, it was automated thru the FMSs which did the calculated and displayed the "reference GS" and produced an aural warning, if the actual GS was less than reference GS. It came out of windshear accidents and the ability of INS systems to show real time ground speeds. I thought it was useful for aircraft which have high momentums and low excess power-the C-5, for example. That said, we still had prohibitions about operations in windshear and TRW conditions.[Unquote]

Thanks for answering my question (in post #5), and I think you have covered about two-thirds of the whole GS-mini subject in just two paragraphs. It confirms my contention that the technique predated the A320. As they say, there is nothing new under the sun.

What you describe, once it had been automated, sounds pretty close to Airbus's "managed" IAS.

You hit the nail on the head when you talk of aircraft that have little surplus power/thrust, like your C-5. Without comparing typical thrust-to-mass ratios on various aircraft, I guess heavy B707s are also underpowered, and presumably B-52s.

B707s were retrofitted with INS eventually, but I don't remember Boeing offering guidance of this kind, which would have been useful. The only "additive" we used to apply to the "bug" (VREF) was a mental one (no objection to that) based on the surface wind (half wind speed + gust, up to a maximum of 20kt). Can't comment on early 747s; but framer tells us that "Qantas boeing crew use RGS or reference ground speed. It basically provides them with a ground speed they don't go below. Works well."

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It's only fair to admit that most twins, including BOAC's and SR71's B737, have the luxury of a good thrust-to-mass ratio in the all-engine case. Maybe that is why they can stick to the old version of energy management on the approach: simply chasing an IAS that is based only on VREF, plus an increment for the wind on the surface – which wind may be zero.

 

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19th November 2008, 02:20   #43 (permalink)

Chris Scott  Join Date: Jan 2008Location: England (N. Downs)Age: 62Posts: 387

Like autoflight, I am increasingly dismayed at the difficulty that so many otherwise intellectually-bright forumites appear to be having to grasp what is essentially a simple concept: the importance of protecting the all-important IAS by not allowing the GS to fall too low when a negative windshear is known to be ahead.

The fascinating – but essentially esoteric – discussions about the precise definitions of inertia, momentum, and kinetic energy are unnecessary in this context, although they might well be worthy of a separate thread. On this one, they amount to little more than fog-inducing semantics. I'm wondering if, in one or two cases, they are inspired by an element of perversity of the "not invented here" variety.

The sceptics constantly emphasise the importance of IAS, and seem to recognise that it can suddenly fall dangerously, due to a loss of headwind; as described by VinRouge (post #27). Their mantra is roughly this: IAS is the only thing that matters; so we must concentrate on it exclusively, and ignore the GS. Wizofoz (post #35) seems to be implying that we, on the other hand, are advocating that GS is more important than IAS.

This is a perverse misrepresentation of my previous posts, which clearly state that the target IAS is always the higher of: the conventional approach IAS (on the one hand); and the IAS which delivers the calculated minimum GS (on the other). So we are always at an equal or greater IAS than he is.

To save readers looking back 3 days, let me remind you that in my first post (#5), I wrote: "...lift requires IAS."I then invited sceptics to look at IAS from a fresh perspective – "IAS = GS plus headwind-component (sea-level/ISA).

Shortage of (GS) can only be corrected by applying extra thrust; for a period of time. On a bad day at the office, that time may not be available."

Two days ago, in post #16 – "You imply that we are ignoring the all-importance of IAS. On the contrary: IAS is precisely what we are trying to conserve."and – "The GS-mini concept protects IAS by constantly offering the pilot an IAS target (managed speed) which results from: the higher of VAPP and the IAS required to achieve the minimum GS."

Quote from SR71,I've touched down in a light 737 at a GS of <90kts on a day when it was gusting 65kts. I didn't even think about GS. The only thing I seek to preserve on finals is IAS. If I fly through a shear, I need to regain IAS surely, not GS?What am I missing?[Unquote]

Does he want an honest answer? Seriously, though, the secret is to anticipate the shear, if you can predict it is going to happen. [If you cannot, that's another topic.] We are not discussing the situation where the wind is strong and gusty all the way down to and including the threshold; it is the sudden predicted suspension of a headwind that concerns us.

SR71 will continue concentrating manfully to regain his target IAS, which he need not have lost hold of in the first place. While doing so, he may have ample time to discuss whether his "scalar" kinetic energy, and the amount it needs to increase, is relative to an unsteady atmosphere, or to a stable platform like the earth's surface; I shall leave him to that.

Mark1234 describes the advantage of (automated) GS-mini: as the headwind falls, taking the actual IAS with it, the target IAS normally falls by the same amount (but never below the threshold IAS). That is because the inertia of the aircraft protects its GS (unlike its airspeed). And remember, TAS = GS + HWC. The minimum GS is the threshold TAS minus the headwind component of the programmed surface wind. IAS and TAS are the same at sea-level/ISA, of course, but usually not elsewhere. The system corrects automatically for the conversion of target TAS to target IAS, which is one of the awkward things to do manually, and therefore invaluable.

 

19th November 2008, 06:19

  #44 (permalink)

Wizofoz  Join Date: Jun 2001Location: Second Camel on the left....Posts: 1,884

Chris, No, I think it's you that unintentionally misrepresented my position.

I've kept out of the minimum GS debate entirely. I understand the concept and have no doubt it works. I shall therefore, when on approach.....Follow my companies SOPs and do as I'm told!! If I'm ever put in a policy making position, I will revisit the whole matter and...Follow the manufacturers recommendations!!

All I have been doing is trying to do is point out several conceptual fallacies to which you seem to subscribe, encapsulated by one of your first statements:-

Quote:

Inertia is a function of GS, not IAS.

Which was untrue at several levels, not least of which being you didn't know the difference between Inertia, Momentum and Kinetic energy, and that you constantly allude to an aircrafts ground speed somehow effecting it's aerodynamic performance.

The only relationship that effects the aircraft is between it and the air around it. Carrying extra airspeed to allow for changes in that relationship is valid. Basing the amount to carry on a fixed datum like the earths surface is also valid. Making pseudo-scientific statements about "Kinetic Energy" and how it should be based on the earths surface is not.

The fact that you still don't get it is shown by your mocking tone towards SR71 when you said-

Quote:

SR71 will continue concentrating manfully to regain his target IAS, which he need not have lost hold of in the first place. While doing so, he may have ample time to discuss whether his "scalar" kinetic energy, and the amount it needs to increase, is relative to an unsteady atmosphere, or to a stable platform like the earth's surface; I shall leave him to that.

Dude, it's that unstable atmoshere we need to keep flowing over our wings, and it is are IAS that is a measure of that flow.The amount you need to change (or, in your method, the extra you need to hold in the first place) is equal to the amount the air is going to change it's velocity relative to your aircraft.

It was you who started (incorrectly) throwing scientific terms around, don't get snitty with someone for correcting you (BTW framer, thank you!).

I also note that you are a greater authority than Boeing on how to fly Boeings, and anyone who doesn't fly as you recommend is open to mockery and criticism

Last edited by Wizofoz : 19th November 2008 at 06:35.

 

19th November 2008, 11:20

  #45 (permalink)

Meikleour  Join Date: Jul 2007Location: ukPosts: 39

Chris,I admire your perseverance in trying to open the minds of the `determindly closed`! Some people will just never get it. It`s a bit like the advocates of wing warping saying that ailerons `will never catch on`

Bon chance mate.

 

19th November 2008, 11:56

  #46 (permalink)

Wizofoz  Join Date: Jun 2001Location: Second Camel on the left....Posts: 1,884

Meik,

I'd be interested to know who you think is showing a closed mind here and how. I for one have stated that I understand the concept of GSmin, and agree it would work. I just don't go around ignoring my Boeing approved and company mandated procedures because someone on PPRuNe made a persuasive argument.

I'll happily fly a min GS approach- The day it appears in my ops manual!!

 

19th November 2008, 13:34

  #47 (permalink)

Chris Scott  Join Date: Jan 2008Location: England (N. Downs)Age: 62Posts: 387

Thanks, Miekleour.

Quote from Wizofoz:I've kept out of the minimum GS debate entirely. I understand the concept and have no doubt it works.[Unquote]Why? It was central to the topic. It was the main element of Olendirk's original post, which was a thoughtful request for an explanation of how the technique works. His question was effectively ruled out as heresy by BOAC (post #3). Referring to anyone who advocated the technique, he wrote: "ignore them - they are mad."Just to ram the point home, he wrote:"IF you choose to do it, the info is on your EFIS, but I suspect any Captain with half a brain would then take control and have you sectioned - I would."

This paternalist scolding seemed to me to be less than helpful. The concept needed to be explained, which I attempted to do in common cockpit parlance. In

Physics terminology, of course, my use of the word "inertia" was wrong – as Wizofoz (and others) pointed out, and I quickly accepted. Since then, the "debate", as he calls it, has consisted mainly of nit-picking.

As Wizofoz understands the concept – and can presumably explain it better than my feeble efforts, would it not be more helpful to do so? There's still time...

Quote from Wizofoz:...you constantly allude to an aircrafts ground speed somehow effecting it's aerodynamic performance.[Unquote]Rubbish. Any quote?

Quote from Wizofoz:...don't get snitty with someone for correcting you [Unquote]Examples?

Quote from Wizofoz:I also note that you are a greater authority than Boeing on how to fly Boeings, and anyone who doesn't fly as you recommend is open to mockery and criticism[Unquote]No. I recommend that pilots remain within the limits of their companies' SOPs. galaxy flyer and framer have provided evidence that manual versions of the concept have been in use elsewhere, since the introduction of INS. Although I attempted to explain a possible procedure to Olendirk ("D.I.Y. GS-mini?", post #17), I included several caveats, and ended it with a strongly-worded warning not to deviate from SOPs. Since then, I have added:"It's only fair to admit that most twins, including BOAC's and SR71's B737, have the luxury of a good thrust-to-mass ratio in the all-engine case. Maybe that is why they can stick to the old version of energy management on the approach..."

The difference between me and many of the pilots on PPRuNe is that I spent 17 years flying approaches on a variety of jet transports, including the underpowered B707, using IAS with SOP-increments, and ignoring any GS read-out. I later spent 14 years flying GS-mini-equipped twins.

The B707-320, with a MLW of 112T and only about 30T (spare us a lecture about Newtons, etc.) of rated thrust, could have benefited from the technique more than most. There is no doubt that automated GS-mini, used iaw SOPs, is a useful and protective system. It is particularly advantageous in the engine-out case.

But both pilots and the A/Thr need to avoid the mistake of using the "managed" IAS as a minimum speed, rather than a target.

 

19th November 2008, 14:00

  #48 (permalink)

BarbiesBoyfriend  Join Date: Jan 2008Location: UKAge: 48Posts: 85

I'd say thinking about your GS while on approach is a bit silly.

All that matters is your IAS and the wind.

On a windy day, if I ve got 40kt on the nose and the surface wind has been passed as 10kt, I know 30kt of HWC is going to disappear at some point. Therefore I fly a bit faster!

Got 10,000 hours now and never had a negative

windshear- so it works!

 

19th November 2008, 14:14

  #49 (permalink)

Wizofoz  Join Date: Jun 2001Location: Second Camel on the left....Posts: 1,884

Quote:

Rubbish. Any quote?

HERE:-Quote:

Inertia is a function of GS, not IAS

HERE:-Quote:

Shortage of inertia (GS) can only be corrected by applying extra thrust

and HERE:- Quote:

As you say, no velocity is absolute; it has to be relative to something. However, astronauts excepted, pilots and humans usually measure it in relation to the local surface of mother earth.

You meant momentum, but were still wrong.

Quote:

Examples?

Here:- Quote:

If it's "Horlicks" to state that, for a given mass, inertia (kinetic energy) is a function of GS, perhaps you can tell us what else? IAS?

(Actually, that belongs in both columns)

And most notabley Here:-

Quote:

While doing so, he may have ample time to discuss whether his "scalar" kinetic energy, and the amount it needs to increase, is relative to an unsteady atmosphere, or to a stable platform like the earth's surface; I shall leave him to that.

If you had simply given an explination of Gs Mini- A way of allowing for windshear by carrying sufficient IAS to allow for it, referenced to a ground speed, all would have been fine. Your delving into iffy physics was always going to be challenged- it is Tech Log after all.

BTW, what happens to an aircraft flying with a large headwind if it quickly turns 180Deg??

 

19th November 2008, 14:16

  #50 (permalink)

Port Strobe  Join Date: Jun 2003Location: GlasgowPosts: 164

So in summary Chris you've been right all along. You agree that we're all agreed we understand how GS mini works, some of us have learned a little about inertia, momentum, kinetic energy of the translational variety and their lack of interchangability, and in the future we'll all fly approaches based on a minimum reference grounspeed to save us from adding thrust to maintain the IAS as this is safer than having an increasing groundspeed throughout the approach. However the practical ramifications of this discussion are we'll still go to work and do as we're told by the manufactuer and any deviations from this approved by our respective employers which are authorised by their NAA all underpinned by airmanship questioning whether or not it is sensible to do so in the present and expected conditions, be they meteorological, proximate traffic its sequence or whatever. Which is a long way of saying what I said on the first page in response to the initial question, when it's managed speed faffing with the command speed then let it do so until you're content however until that day arrives then do as instructed. Which you said you're also in agreement with. Agreed we're all agreed?

 

19th November 2008, 14:18

  #51 (permalink)

Meikleour  Join Date: Jul 2007Location: ukPosts: 39

Wizofoz,What makes you think I was referring to you?!

If your main arguement is `comply with one`s own company SOP`s` then we are in complete agreement! HOWEVER that was not the reason for the original thread. On the three Boeing types I have flown (B707,

B737, B747) the maximum Vref increment was +20kts. I also flew with one operator who used the minimum reference ground speed concept on these types. The problem arises when the expected change in headwind component decreases by more than that amount. To berate Chris about his use of scientific terms and to quibble about frames of reference misses to whole point of the arguement! An Airbus, using mini-GS arrives over the threshhold at a SUITABLE GROUND SPEED and a SAFE IAS!

QED

 

19th November 2008, 23:44

  #52 (permalink)

SR71

Mach 3 Join Date: Aug 1998Location: StratospherePosts: 397

Chris,

I'm bowing out at this point...

Like the Wizard, I understand what the concept you allude to is seeking to guard against but I (also) objected to your use of terminology and the constant reference to GS.

To have a sensible discussion, one has to use the right terminology. I'm sure you agree.

I let you know early on I was a pedant.

 

20th November 2008, 02:41

  #53 (permalink)

john_tullamarine Moderator Join Date: Apr 2001Location: various places .....Posts: 3,086

might be a suitable time for some of the folks to have ten deep breaths .. the forum isn't about sheep stations .. only looking for reasonable and rational discussion on the topic. If this one or that has a different view, that's fine .. as always, the aim is to play the ball, not the player.

 

20th November 2008, 02:45

  #54 (permalink)

krujje  Join Date: Jan 2007Location: The QCPosts: 50

Quote:

as always, the aim is to play the ball, not the player

but are we measuring the velocity of the ball relative to the players, the court, the air, the earth, or the sun...?ah! forget it...

 

22nd November 2008, 05:03

  #55 (permalink)

autoflight  Join Date: Jun 1999Location: Brisbane, AustraliaPosts: 127

I flew military & airline for 38 years and only recognised a microburst one time. It seemed that the initial outward wind was about 80 knots. If that was on your final approach and you ignored all the evidence, expect a near instantaneous loss of 160 knots of IAS. Unrelated to the loss of speed would be an increase ROD due to the rapidly decending air. Please nobody tell me this is a survivable event! Avoidance is the only reasonable course. I am also concerned that a few jet pilots out there still don't understand that an indication of impending loss of IAS is when G/S on final is lower than speed calculated using tower reported wind. A moderate shear will show as a G/S perhaps 10 - 15 knots less than the calculated touchdown G/S. This might not be an indication of a microburst. If you expected a G/S of 120 knots and at 500 ft, with a stabilised approach, it is 70 knots, I would call that very significant windshear, probably with worse to come. This could be a MB. All your worries about how your kids will turn out, will your marriage last, will you have a successful retirement, will probably disappear with you, your crew and pax in a smoking hole in the ground short of the runway.You don't have to actually fly G/S. Just make sure you don't go much below it. If you're not able to force yourself to do this because you were trained to fly IAS, at least keep an eye on it to assist in identification of perilous conditions.

Last edited by autoflight : 8th December 2008 at 20:50.

 

22nd November 2008, 08:59

  #56 (permalink)

BOAC Per Ardua ad Astraeus Join Date: Mar 2000Location: UKPosts: 9,068

Well, I 've been doing JT's 'deep breathing' for a couple of days and returning now to read the thread I have to say that in my opinion 'Port Strobe' has said it all. As I said to Olendirk on Post #3, Quote:

Originally Posted by PS However the practical ramifications of this discussion are we'll still go to work and do as we're told by the manufactuer and any deviations from this approved by our respective employers which are authorised by their NAA all underpinned by airmanship questioning whether or not it is sensible to do so in the present and expected conditions, be they meteorological, proximate traffic its sequence or whatever.

- i.e. when your 737 operating company TRAINS you to fly g/s on finals, learn how to do it and do it well. Until then, fly your company procedures - and conform to ATC speed request, of course, as always.

 

24th November 2008,   #57 (permalink)

10:19

autoflight  Join Date: Jun 1999Location: Brisbane, AustraliaPosts: 127

It is quite rare for me to specifically identify those with a contrary view, but in the interest of flight safety I ask that less credibility be given to the entrenched opinion of those absolutely opposed to G/S considerations.

 

24th November 2008, 11:22

  #58 (permalink)

Capt Pit Bull  Join Date: Aug 1999Location: EnglandPosts: 635

Looks like I'm a bit of a 'johny come lately' and missed most of the good bits!

One problem here is that its very common for people to build their understanding of principles of flight on a foundation of dodgy Physics. Most of the issues have been thrashed out above. I know it might sound pedantic, but things like mass, inertia, momentum and kinetic energy are often not just slightly different but are truly radically different quantities.

I think momentum and kinetic energy have been well dealt with above. A brief summary:

Momentum. mv. A vector quantity. Conservative (in a given system, total momentum is always conservative, this is intimately connected to Newton 2 and 3). Pitbull top tip: Use changes of momentum to figure out how long a TIME it takes for a force to cause a change.

Kinetic Energy. 1/2mv^2. A scalar quantity. NOT conservative (total energy is conservative, any given form isn't). Pitbull top tip: Use changes in Kinetic Energy to figure out how long a DISTANCE it takes for a force to cause a change.

So we can see, they are different in pretty much every way. Don't let the fact they both have an M and a V in them fool you into assuming they are very similar - they aren't!

What about Inertia and Mass then? Not sure this has been properly dealt with. There are two aspects to mechanics, translational and rotational. Everything above (I think) was about translation, i.e. an object moving around in its frame of reference. However, there are almost identical concepts relating to the rotation of objects.

e.g. We know (Newton 1) an object will maintain a given velocity unless acted upon by an unbalanced force. The rotational equivalent is that an object will maintain a given rotational speed and orientation in space unless acted upon by an unbalanced Torque. There are equivalent concepts for momentum and angular momentum, kinetic energy and rotational

energy and so on.

Inertiais a term that applies to both parts of mechanics. It is, in general, the reluctance of a body to change what its doing. The reluctance of a body to be moved is its mass. However an objects mass does not tell us much about the reluctance of a body to change its rotation. For this we need a quantity that describes not just the mass but also the distribution of the mass (remember your basic gyro theory?). This is the moment of inertia.

So, Inertia is a general term that encompasses both mass and moment of inertia.

As such, mass and inertia are not strictly identical to one another, but rather mass is a subset of inertia.

However, if you are only talking about translational mechanics then you can petty much get away with using the terms interchangeably.

Clear as mud?

pb

 

24th November 2008, 14:02

  #59 (permalink)

BOAC Per Ardua ad Astraeus Join Date: Mar 2000Location: UKPosts: 9,068

Quote:

Originally Posted by a/f I ask that less credibility be given to the entrenched opinion of those absolutely opposed to G/S considerations.

- if that salvo was fired at me, you should aim more carefully. Please note I have never said I am 'opposed to G/S considerations', merely that I would be tempted to have an F/O placed under restraint in a 737, or use the Rainboe rolled-up newspaper technique if he/she flew that way in contradiction to company procedures, and I would personally deliver him/her to SATCO for a whipping if he/she neglected to fly ATC requested speeds.

I happen to think it is an extremely valid way to approach approaching and a spiffing idea, OK? Jolly

good wheeze for an Airbus, Ginger.

 

24th November 2008, 23:00   #60 (permalink)

autoflight  Join Date: Jun 1999Location: Brisbane, AustraliaPosts: 127

ATC requested speeds are nothing to do with avoiding dangerous windshear. Avoiding windshear difficulties is not type or company

specific airmanship. Narrow minded and outdated company policies are items requiring official adjustment rather than blind obedience. Anyone who has made thousands of Prunne posts can surely put an approach speed proposal to his company rather than threatening F/O. Is this sufficiently directed?Great post Olendirk. This subject obviously needs to be out there, but this is my last word.

Last edited by autoflight : 24th November 2008 at 23:20.

Quote:

but this is my last word.

- noted. For those who are still here, I can confirm PPRuNe post tally (aka Aunt Mary') has no relevance to Boeing procedures.Quote:

can surely put an approach speed proposal to his company

- I think he is pulling my leg

IF Olend is still around, by all means approach your company to re-write Boeing handling procedures and have the relevant software fitted. I still maintain you should follow your trained procedures and fly IAS. We ALL (I hope) are aware of windshear without a computer to help us? Hopefully 'airmanship'/commonsense has not yet been eradicated?

 

25th November 2008, 13:38   #62 (permalink)

Boingboingdriver  Join Date: Dec 2005Location: EuropePosts: 52

I totally agree with BOAC,Why changing a procedure to fly IAS to GS?When u fly at approach speed and you have a 20 kts tailwind..do you actually look at your groundspeed?I dont.When will one tell his FOs the great idea to use take off speeds using GS!!!

I doubt these guys are a few dangerous ones who just forget to fly,distracted by their own irrelevant theories added through the years...And whats that with IRS?INS......dudes!!!!!just fly the plane the boeing way...experiment your way if you are the captain(god bless you)but dont teach it and

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use your rank to fill these poor new fos with this nonsense...

Regards

Captain standard.

 

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25th November 2008, 15:16   #63 (permalink)

Wizofoz  Join Date: Jun 2001Location: Second Camel on the left....Posts: 1,884

Autoflight,

This, then. would be why all those hundreds of Boeings have been falling out of the sky for all these years.....

 

26th November 2008, 06:03

  #64 (permalink)

dream747  Join Date: Nov 2006Location: TropicsPosts: 124

GS Mini

I've been following this topic with interest and I have also found one great post that clearly explains GS-mini.

GS-Mini, Auto-thrust, and Short Runways – Airbus A320/330/340

The 4th post in the thread by Norman Stanley Fletcher.

 

26th November 2008, 08:44

  #65 (permalink)

BOAC Per Ardua ad Astraeus Join Date: Mar 2000Location: UKPosts: 9,068

Dream - I guess most of us understand that system - what we are awaiting is for autoflight and others to give us details of the 737 GS Mini system so we can start using it

 

1st December 2008, 11:41   #66 (permalink)

Jumbo Driver  Join Date: Jun 2000Location: UKPosts: 320

Good morning everybody - sorry I'm late.

Right, what's all this about then ... ?

JD

 

1st December 2008, 13:27   #67 (permalink)

BOAC Per Ardua ad Astraeus Join Date: Mar 2000Location: UKPosts: 9,068

JD - having woken a dying thread, you might as well roll up your sleeves and get stuck in!

 

1st December 2008, 14:34

  #68 (permalink)

Basil  Join Date: Jun 2001Location: UKPosts: 997

Norman Stanley Fletcher,

Just read your very comprehensive explanation.

A previous mixed fleet employer used to go on a bit about min GS BUT I was flying the 747 classic and I felt, on that aircraft, trying to monitor and adjust for GS was too distracting and it was better to stick to the Boeing additive of Vref + 1/2 wind + Gust tapering to Vref + Gust at threshold.

Anyone regularly use the min GS system on a steam driven aeroplane

TCAS RA at Aircraft's Certified Ceiling

Hi, I am just wondering what would happen if you are cruising at or just below the certified maximum altitude and a tcas ra goes off? You obviously can't climb higher so what do you do?

Thanks

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4th October 2008, 20:13   #2 (permalink)

Port Strobe  Join Date: Jun 2003Location: Glasgow

Compared to doing nothing climbing is the better option is it not? Its not the absolute ceiling so there will be some room left to manoeuvre within and maybe 10 - 20 knots of speed to trade in short term,

Posts: 164 possibly a good reason not to climb to the maximum possible altitude straight away? If its that tight a margin on performance then perhaps the operator should mandate you put the transponder to TA only? Just a few thoughts, but I reckon following it as best you can would be the best bet.

 

4th October 2008, 20:23   #3 (permalink)

EMIT  Join Date: Aug 2007Location: The NetherlandsAge: 52Posts: 82

ACAS Bulletins

Like the previous poster replied - follow TCAS command, taking whatever performance the aircraft gives to you.

Matters like this are addressed in an excellent way in the ACAS bulletins published by Eurocontrol, use the following link

EUROCONTROL - ACAS II Bulletins and Safety Messages

Underlying address is as follows, should the link work incorrectly from your browser. On the page that you reach with the address below, you will find a link to the 10 bulletins that have been published to date.http://www.eurocontrol.int/msa

edit: corrected address specification

 

4th October 2008, 22:10   #4 (permalink)

Founder  Join Date: Jan 2006Location: Sweden & FinlandAge: 27Posts: 314

Most often max certified crz level is not an absolute level as someone above stated. It's often a certified altitude of a 2 % buffet margin or sometimes higher depending on the aircraft. Also governing the max crz alt is the maximum cabin pressure differential. But there is always a safety margin built into that so the aircraft most often can climb all the way up to an absolute altitude...

so always follow TCAS what ever it might say.

As a note, you should be aware of the new communication prescribed in case of a TCAS RA issued by ICAO in May 2008.

Safe flying!

 

4th October 2008, 23:01   #5 (permalink)

Mad (Flt) Scientist  Join Date: Sep 2002

A review of this thread may be useful. TCAS is inhibited where the aircraft performance is inadequate to respond to the RA, this would apply for this case

Location: La Belle ProvincePosts: 1,250

too.

 

5th October 2008, 10:55   #6 (permalink)

JAR  Join Date: Feb 2000Posts: 56

Embraer 195 ceiling 41000' TCAS:

"No Climb commands or Increased Climb commands are issued at orabove 34000 ft MSL."

 

5th October 2008, 11:30   #7 (permalink)

ASFKAP  Join Date: Dec 2001Location: EuropePosts: 1,309

Quote:

Does TCAS know what you can and can't achieve ?

Yes it does, when the system became mandatory at about the turn of the century, I was busy installing it into a lot of aeroplanes. I distinctly remember installing a particular fit into a B737-200 which would then be used to gain the STC for installation into other 737-200s so there was a lot of FAA testing and inspection involved. From memory I know there was an input from the flap switches (F40 to be precise) to ensure that with the flaps at 40 a climb RA would never be issued regardless of the scenario, there was also an input from the air data computers to ensure that at max certified altitude there would not be a climb RA generated.In testing we had to recreate these scenarios with test equipment and it all worked as advertised....

Just to elabourate on the answer I gave in that previous thread. I remember during the testing of that part of it the max certified altitude to which TCAS was not allowed to issue a 'Climb RA' was actually much higher than the max altitude the A/C would usually operate at, I can't remember the exact figure but it was either 40000ft or 50000ft.

 

5th October 2008, 15:59   #8 (permalink)

galdian  Join Date: Dec 2006Location: australiaPosts: 268

Hi Mad (Flt) Scientist

Only because some things stick in the mind, whilst others don't, would I have posted that TCAS will not issue RA's outside of the aircraft's current performance capabilities to achieve the RA regardless of specified

aircraft limitations so spot on.

Then begs the question - if TCAS recognises danger but also recognises a lack of performance ability what

happens ??Does it re-work any possible options to avoid the conflict - or does it default to (literally) throwing it's arms in the air and saying "too hard, not my problem!!"

Just wondering.

 

5th October 2008, 16:59   #9 (permalink)

CJ Driver  Join Date: Aug 2003Location: ScotlandPosts: 115

Cooperative solutions

If both aircraft involved in a conflict have TCAS, then between the two TCAS systems they will agree a solution. For example, if you are at Max Altitude, and someone is climbing to your level, although you may not be able to go up, they will still be told to reduce or stop their climb.

If TCAS cannot give you a resolution because of inhibit logic, it will give you a Traffic alert instead and let you figure something out. Actual inhibit inputs are airframe dependent, but can include air data inputs (altitude), gear position, flap position, and so on.

Slight change of thread - is it just my imagination, or have there been quite a lot of fairly basic TCAS questions on PPRuNe? I don't want to be rude, but isn't "everything you ever needed to know about TCAS" taught in pilot school any more?

Although there are lots of clever algorithms inside the box, the end result is actually pretty simple, and (at least I always thought) completely understandable in about 5 minutes.

 

6th October 2008, 05:14   #10 (permalink)

Chirpie  Join Date: Sep 2008Location: Incredible IndiaAge: 49Posts: 3

TCAS has priority

Hi folk,If the question is from a 320 "Busdriver", the answer is that you will follow the RA. The 320 alt limit is more a result of Engine thrust avail than the aerodynamics of the aircraft. The aircraft is able to momentarily climb above without a problem.Follow the RA in all cases - except one. That is if you get an additional GPWS warning of "Terrain Pull Up". Then the GPWS warning takes priority. You may miss the traffic but if you don't follow the GPWS you won't miss the ground.

 

6th October 2008, 20:51   #11 (permalink)

Cat1234  Join Date: Oct 2000Location: AustraliaPosts: 11

Max Certified aircraft altitude is setup with hardwired jumpers into the back of the Tcas computer. When I have tested aircraft on ground with the test box using a scenario of two aircraft at or near Max altitude and a conflict the RA is co-ordinated with sufficient time to prevent aircraft having to climb.

 

6th October 2008, 21:37   #12 (permalink)

bflyer  Join Date: Dec 2006Location: N33 24.7 E36 30.8 E 36 30.8Posts: 152

Hi...this is from a paragraph in a book titeled AIRCRAFT DIGITAL AND ELECTRONIC COMPUTER SYSTEMS quote: It is important to be aware that TCAS provides only vertical guidance...TCAS also ignores performance limitations, in other words, when flying at maximum altitudes, TCAS may still generate a climb command unquote:

now the term max altitudes was not elaborated upon so i don't know what to make of itbf

 

6th October 2008, 22:23   #13 (permalink)

Miles Magister  Join Date: Oct 2001Location: EnglandPosts: 251

I believe that you have 1.3g to the buffet margin at max cert alt. That gives you plenty of room to manouvre at the height if you really need it. I would suggest in the case of an RA you need it. It is perfectly safe and reasonable, however your AFM is the authority.

MM

 

10th October 2008, 10:55   #14 (permalink)

Meek  Join Date: Sep 2007Location: MaltaAge: 39Posts: 13

Chirpie

A320 is certified to 39800 feet so if you are flying U.S. or Europe, not a problem.

Last edited by Meek : 10th October 2008 at 10:58. Reason: title

 

10th October 2008, 14:20   #15 (permalink)

PEI_3721  Join Date: Mar 2006Location: CanadaPosts: 119

Miles Magister, a reminder to avoid any misunderstanding, the 1.3 buffet margin is a turning flight requirement. TCAS manoeuvres are only vertical and are approximately defined by pull up (1.25 g), reaction time, and the required altitude/rate change; these factors (and configuration if applicable) define the TCAS limit at maximum altitude.

 

10th October 2008, 16:08   #16 (permalink)

bflyer  Join Date: Dec 2006Location: N33 24.7 E36 30.8 E 36 30.8Posts: 152

PEI 3721......is the 1.25 pullup limit fixed for all altitude or does it apply to a certain level only?

 

10th October 2008, 19:56   #17 (permalink)

PEI_3721  Join Date: Mar 2006Location: CanadaPosts: 119

bflyer, the figures that I quoted were approximate, I do not know for sure that theyapply to all altitudes.

The Eurocontrol hosted document Operational use and Pilot training guidelines indicates that the maneuver requirements assume increments between 1/4g to 1/3g (1.25 – 1.33g) depending on the alert, and that the required VS is achieved in 2.5 sec; the information suggests that these apply at all altitudes. The technical information in this document should be crosschecked with the latest ACAS technical spec as some performance aspects may have changed with recent updates.

ACAS Training materials.

 

10th October 2008, 21:30   #18 (permalink)

fellman  Join Date: Oct 2007Location: UKPosts: 6

Not quite right PEI_3721.The required VS will be reached in however long it takes using the specified acceleration. The times quoted in the guidelines are the delay from the issue of the RA to the pilot moving the stick.For an initial RA the required acceleration is 1/4g with the manouevre starting no longer than 5 seconds after the RA is issued.For a subsequent change in RA the required acceleration is 1/4g (for weakening RAs or "normal" strengthening RAs) or 1/3g (for RA reversals and RAs strengthening to "INCREASE CLIMB"/"INCREASE DESCENT") in both cases starting no longer than 2.5 seconds after the change in RA is issued.These accelerations and times are indeed applicable at all altitudes.

 

11th October 2008, 04:20   #19 (permalink)

Lookforshooter Banned... Persona Non Grata Join Date: Sep 2008Location: AsiaPosts: 77

This is all assumes of course that the robots flying the plane do exactly with the RA tells them to do. This is where judgement takes precident over a box.Your right in the coffin corner, do you climb because the RA tells you to? Your on approach at the MDA, IMC, do you decend because the RA tells you too? Your VMC right

below the clouds on a visual approach...do you climb into the soup because the RA tells you to? I bought a TCAS I unit and chose not to go TCAS II for the extra $100k...I figured, the pilot should know when to climb or descend.

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11th October 2008, 14:30

  #20 (permalink)

PEI_3721  Join Date: Mar 2006Location: CanadaPosts: 119

Thanks for the clarification fellman. Are you quoting from the same training reference that I used?The Eurocontrol training materials link has another reference stating ‘5 sec’, but without specific application, i.e. 5 sec from alert to achieved VS, or 5 sec during the maneuver – its unclear.

My recollection during testing a system many years ago was of 2.5 sec ‘surprise’ (reaction) time plus 2.5 sec maneuvering. The use of ‘g’ in a specification is fine providing the aircraft has an accelerometer, but in practical terms, a pilot requires specific guidance as to what a ‘smart’ maneuver is. Some of the training materials provide values of pitch change for speed, but the rate of pitch and feel of the maneuver will be aircraft specific, so practice is required.

Lookforshooter, the main point which has been made in many threads on ACAS is that pilots must follow the RA. This is a matter of discipline – airmanship.As already stated, when an aircraft is at it’s maximum altitude, no Climb instruction will be given so the pilot does not have to consider performance, nor weather. There are similar safeguards at low altitude so that ACAS will not demand hazardous flight towards the ground.

A danger in aviation is from those pilots who figure that they know better than the system. If you do not follow a RA then you may cause an accident – it will be your accident as you will be part of the collision; no thinking, no judgment, just follow the RA.

PEI_3721: This reminds me of how some people look at anti-lock brakes...they trust the box to do the braking. In fact, on one of the planes I fly, I had a chance meeting with a guy that was part of the certification process. He stated the test pilots could beat the braking distances about 35% of the time. That said, they didn't beat it was by much, so just mashing down on the brakes and letting the box do the work is the defacto braking method for most pilots. Does Nascar install anti-lock brakes: No. I

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have landed on very slick runways, snow, ice...gravel, ect where the box just coldn't figure it out, and I just kept going. TCAS: I gave some exampes where listening and doing what the RA tells you do, could get you in trouble. I can't speak for airliners, but TCAS installed in the planes I fly, can only tell you to climb or descend...not turn right or left, or slow down, or wait and see, or whether there is a radio tower just below you..on and on. Again, if the pilot can't make a judgement a judgement call, you might as well, have my Pomeranian flying the plane.

 

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11th October 2008, 21:08   #22 (permalink)

PEI_3721  Join Date: Mar 2006Location: CanadaPosts: 119

Lookforshooter, any aircraft fitted with ACAS – commercial or GA – will only have vertical, climb or descend type commands. There is no turning flight associated with ACAS in any aircraft type.ACAS is designed not ‘to fly you in to trouble’, indeed it does the very opposite and provides information of how to avoid trouble.All aircraft have essentially the same system, thus whether a large or small aircraft, commercial or GA, all pilots must follow the commands; if someone does not, then there is an accident waiting to happen.

Commercial aircraft are flown by professionals who have the required airmanship / discipline to obey ACAS.History may identify the one dominant accident involving ACAS as a problem of worldwide communication – ensuring that all crews, operators, and national authorities work to the same set of rules. The lessons have been learnt from that accident; the international rules are now firmly established.A remaining weakness is with those humans who do not seek the necessary knowledge to understand both the principles of the system and the rules for its operation. Yet even with these, the individual must overcome bias and mis-belief, and follow the ACAS commands.

I and probably other pilots would have concerns about your apparent weaknesses in knowledge and resultant attitude about ACAS, but the most worrying aspect is that if you don’t correct these, you might be in the same airspace as us.

Re brakes; apart from mixing up anti skid with

autobrake – functionally different systems, but usually combined in the same box; you are correct about the effectiveness of manual braking. In fact any pilot can better the braking distance achievable with RTO/Max autobrake providing that s/he applies the brakes quickly and maintains maximum pressure until stopped, i.e. follows the rules.

 

11th October 2008, 21:38   #23 (permalink)

Lookforshooter Banned... Persona Non Grata Join Date: Sep 2008Location: AsiaPosts: 77

While I understand the robotic airline flight crew approach that is taught to blindly go where the TCAS box tells them to go, I don't think most passengers will..it didn't help the pax on the mid air in Europe. As far as weakness in knowledge ....ahhh another aviation expert to to tell us how it is....your not qualified to make any judgement on aviation knowledge or experience based on a few internet posts, no one is. If you have to resort to insults in the face of a rational logical discusion...that means you can't discuss the facts presented. Insults are the refuge for the weak minded.

 

11th October 2008, 21:58   #24 (permalink)

Mad (Flt) Scientist  Join Date: Sep 2002Location: La Belle ProvincePosts: 1,250

"Blindly" following TCAS guidance is no different to "blindly" following windshear escape guidance, or flight director guidance in autoland, or any of a number of other cases. Yes, there may be one chance in a billion that the systems have gone u/s and are giving you misleading guidance. That's the defined certification risk, after all. But there's a great deal more than one chance in a billion that someone doing their own thing by the seat of their pants will, in fact, do the wrong thing (or a worse thing) and will create more trouble than they were in to start with.

Is the TCAS RA the optimum solution to every single encounter? No, but it's a reliable solution.

Just as in the brakes case: is the anti-skid the very best you can get? No. Maybe you can beat it by a few %. But if you try to do so, you may also screw it up and fail by more than a few %. Now, if your ALD and LFL were based on "the box", there's no upside in being a couple of hundred feet short - and a huge downside in being long, if the runway is limiting.

The entire system is set up on the assumption that the person sat in the left seat is not an expert - there's a huge community behind the procedures, some of whom are experts. Following the advice of the experts, as encompassed in SOPs, is rarely a bad idea.

 

11th October 2008, 22:30   #25 (permalink)

Lookforshooter Banned... Persona Non Grata Join Date: Sep 2008Location: AsiaPosts: 77

Mad - I don't trust my FD to tell me to turn left, but the other 5 things set up, in disparate equipment and systems to verify that I should turn left. Not to mention a sense of dead reckoning, and understanding of where I am at in the flight, what ATC is doing, and how they are equiped. I don't sit back and just hope my F/D is working. I sure hope pilots aren't just sitting back, crossing thier arms, hoping the autoland works...???!! !@!$

 

11th October 2008, 22:32   #26 (permalink)

skiingman  Join Date: Oct 2004Location: New MexicoAge: 24Posts: 35

Quote:

Does Nascar install anti-lock brakes: No.

And Formula 1 banned traction control. Hint: Not because F1 drivers are faster without it. Because they make more mistakes without it. And mistakes are fun to watch when they aren't in large transport aircraft. And despite the validity of MFS' statements about designing systems for non-experts, these systems were designed for experts, and outperformed those experts.

I'd love to know who you fly for so I can remember to stay clear.

 

12th October 2008, 01:59   #27 (permalink)

PEI_3721  Join Date: Mar 2006Location: CanadaPosts: 119

I persevere with this thread, particularly as the issue is of great importance to all of the industry.ACAS relies on appropriate behaviour of both parties in the event of a conflict, thus there is need for a knowledgeable, universal, well discipline approach to flight operations.The availability of ACAS in small / GA aircraft implies that those pilots also require a similar high standard of operation (with respect to ACAS) to those in commercial operations.Whereas a pilot of a small/GA aircraft, with poor understanding of some basic aspect or who has a macho attitude, might suffer a landing (or any other) accident, the result affects only that individual and hopefully no one else. But an inappropriate response to ACAS could result in an accident involving an unwitting third party including many passengers in a commercial aircraft.

If a GA pilot decides not to follow an RA then the commercial safety situation may be no better than it was when the need for ACAS was first noted – Cessna 172 / MD 80 collision.

I am not suggesting that all small / GA operators lack operating qualities, indeed the vast majority (as have commercial pilots before hand) have demonstrated the necessary skills, and strive to improve them before moving on to larger aircraft.The issues are the immaturity of some people, their reluctance to learn, or poor attitudes in an operational climate where there is little or no oversight, operator / regulatory control, or a second crew member to monitor. Worst still is that a few, hopefully very few, might progress to the very light jets with opportunity to really mix with the larger aircraft.

 

12th October 2008, 04:26   #28 (permalink)

galaxy flyer  Join Date: Dec 2002Location: Quabog Valley, USAAge: 56Posts: 875

Lookforshooter

If you have TCAS II on board, you are legally obligated to follow RA commands! To not do so, puts everyone at a risk far greater than not doing so. You can have any opinion you want, but you must follow the commands, PERIOD. Yes, at this stage, only up or down plus "monitor Vertical Speed". Follow for my family's sake

SSG V1.10 lives on, to the endangerment of all, it seems.

Quote:

Terrific..some more holier then thou pontification from the airline sector...which has caused more loss of life in aviation related incompetence then any other sector could in the next hundred years.

Care to produce a few facts to back up that outrageous claim?

 

12th October 2008, 10:12   #29 (permalink)

Denti  Join Date: Mar 2001Location: Somewhere down the road...Posts: 508

Quote:

Add up all the GA deaths vs Airline deaths, see who wins.

Between 1987 and 2007 the GA (nonscheduled air taxy operation, CFR 135) caused 1030 deaths and in the same timeframe scheduled airline operation (CFR121) caused 49 deaths. That is taken directly from the NTSB database. Since GA flies a lot less hours as well scheduled airline operation is several hundred times more unlikely to kill someone than GA is.

We had that little piece of statistics allready ssg, however you still spout the same nonsense. Time to wake up and leave that little cozy dreamworld of

yours.

 

12th October 2008, 13:41   #30 (permalink)

Capt Pit Bull  Join Date: Aug 1999Location: EnglandPosts: 635

Forum search FTW.

Go back and read the previous thread quoted by Glueball. In detail. There is too much dogma on this thread.

RAs should not be ignored. But if you think that any RA that is given to you is gaurunteed to be achieveable, you're cruising for a bruising.

Quote:

If you have TCAS II on board, you are legally obligated to follow RA commands! To not do so, puts everyone at a risk far greater than not doing so.

Actually, that's not true.

There is an important distinction to be made between 'not following' (which is riskier, but only slightly) and 'manouvering opposite' (which is far far riskier).

This may seem like I'm laboring a point, but if you look at the really nasty TCAS incidents (including the ones that would have been collisions if there hadn't luckily been some horizontal separation) a regular feature is people manouevering opposite. Whereas there are plenty of times where RAs have not been followed and with low risk.

When pilots are told "follow the RA, always, thats all there is too it" then they are receiving incomplete guidance. The bean conters love it - a single sentence in an ops manual is cheap; proper training isn't.

It is very possible to receive an RA that is unachievable and/or otherwise unsafe. In those circumstance crew need to know what to do to minimise the risk. In my experience as a trainer if you tell people they mist follow the RA, and then give them a situation where they can't, there is a good chance they will do something really stupid unless they have a good alround knowledge of the system and other collision avoidance techniques.

To answer the Original Poster:

You follow any RA that is generated, whilst being sure to protect the aircrafts flight envelope. If the RA is a climb, and is not achievable, do your best to achieve the best rate of climb, even if its only a few hundred feet a minute, and get as close to the green arc/segment as possible.

UNDER NO CIRCUMSTANCES think "We cant get over him, we must descend!"

If you see the other aircraft, the curvature of the Earth will probably make it appear to be well above the horizon. UNDER NO CIRCUMSTANCES discard your RA in favour of your visual perception of relative altitude and commence a descent.

In other words UNDER NO CIRCUMSTANCES manoeuvre opposite the RA.

pb

 

12th October 2008, 21:45   #31 (permalink)

galaxy flyer  Join Date: Dec 2002Location: Quabog Valley, USAAge: 56Posts: 875

The TCAS won't descend you into a mountain, EGPWS has priority. Yes, Pitbull, if you don't follow the RA, the coordinating aircraft will have a RA of greater magnitude, but following it is the correct response. The San Diego B727/C172 crash occurred when the pilot's thought they had there traffic "in sight" when the real conflict was not in their sight. If they had a TCAS II RA, decided the plane they had in sight was not really a conflict, they would have had the mid-air. Follow the RA.

The German mid-air was caused by pilots following the ATCO's instructions, rather than following the RA. This isn't brain surgery-TCAS is a "last ditch", save your butt device, not an alternative ATC device, as our friend SSG V1.10 would believe. It has saved me twice in civil aircraft and several other times in mil ops. I investigated a crew that decided they were smarter than the ATCO and the TCAS-nearly created a mid-air!!

GF

SSG: You have been shown to be in error and dangerous by any number of Ppruners that are experts in aviation, in all disciplines-pilots, engineers and operations types-a smarter man than you would retreat and try to learn, as opposed to continued idiotic posts.

 

12th October 2008, 22:04   #32 (permalink)

Denti  Join Date: Mar 2001Location: Somewhere down the road...Posts: 508

Quote:

Denti...your numbers are incorrect, all I have to do is find airline crash after airline crash and find more then 49 deaths, in that ten year period.

Actually, you are right (of course, its 19 years, not 10, but basic math isn't your forte), i did use the wrong table. In that period scheduled airlines caused the

death of 1966, with an average rate of 0,0174 deaths per 100.000 hours, vs. 0,775 deaths per 100.000 hours in CFR 135 operation. Or to say it differently, flying GA you have 43,39 times higher chance to die than flying scheduled airline services. Airline statistic shows data per 100.000 take offs or miles as well, sadly that data is not available for GA.

The trend in both types of operation is very nice indeed as fatalities become less common in the last few years.

About the TCAS thing, i dont know how much training others get, but it is a normal piece of training every six months in our simulator sessions, and of course EGPWS has priority over TCAS.

 

12th October 2008, 22:20   #33 (permalink)

PEI_3721  Join Date: Mar 2006Location: CanadaPosts: 119

The person behind Lookforshooter, is either a very misguided non pilot, or a pilot who should be identified and reported to his authority under the terms of a safety report; in either instance, s/he could be added to a PPRuNe ignore list.Alternatively, granting Lookforshooter some semblance of intellect, the debate is with an individual who wishes to devil subjects with very biased views. In some circumstances there could be merit in eliciting information this way. However, there is a fine line between such arguments and the promotion of false information which the unsuspecting or unwary pilot reading PPRuNe might take as the truth, and thus reduce flight safety.In this forum, this form of debate is hazardous at least, and IMHO unethical amongst such a well respected open minded group.I do not know which of the above views is more accurate.I still have a choice, in both what I read and what I believe; I align my understanding with the peer reviewed, expert, and majority views to help maintain a good safety record in our industry.

Last edited by PEI_3721 : 13th October 2008 at 00:32.

 

12th October 2008, 23:12   #34 (permalink)

Blue Coyote  Join Date: May 2006Location: LancashireAge: 46Posts: 17

Lookforshooter

This is a seriously uneducated individual as far as TCAS/ACAS goes. Based on his input to this thread I hope he stays in Asia as I don't want to be anywhere near his accident when it eventually happens.

 

13th October 2008, 01:50   #35 (permalink)

john_tullamarine Moderator Join Date: Apr 2001Location: various places .....Posts: 3,086

After being reasonably well behaved, Lookforshooter has overstepped the mark considerably and been consigned to a gloomy place.

Protocol wise, my concern with him was not his lack of technical and procedural wisdom (that being addressed adequately by dissenting posts - indeed, such robust discussion is good for the education process of those coming up through the ranks). However the lack of civility and manners is out of line - when any poster descends into the depths of ill-considered and persistent personal attack it is sin bin time ...

 

13th October 2008, 04:01   #36 (permalink)

PEI_3721  Join Date: Mar 2006Location: CanadaPosts: 119

NonFlushingLav, “… I never saw a TCAS unit installed that talked to the ground prox …”

Time to look again; commercial installations have priority logic, probably in the alerting system. In very unusual and difficult circumstances the pilot is not confronted with conflicting messages and thus does not have to make a decision.

“CS 25 AMC 25.1322 Alerting Systems6.7 There should be only one aural signal at a time. If the possibility of two or more aural signals at the same time cannot be avoided it should be shown that each signal is clearly intelligible to the crew. The order in which the signals are presented should be that in which crew action is required.”

Re SOPs, often there is need for considered debate about SOPs, the good ones, poor ones, personal SOPs, and those which are ‘rules’. ACAS SOPs are rules with very few exceptions.

 

13th October 2008, 04:31   #37 (permalink)

SNS3Guppy  Join Date: Oct 2005Location: USAPosts: 1,671

Quote:

I never saw a TCAS unit installed that talked to the ground prox, then argued with each other over who took precidence. The fact is, each unit operates independently...one worries about traffic the other about terrain. Both can and will squak, and have squaked at me in the pattern at mountainous airports at the same time. The fact is if you have a flock of airliners above you, mountains below...the PILOT will have to make a decision, not the box.

Actually, that's precisely what TCAS II does.

With respect to the recent conversation on inhibited TCAS commands, my AOM includes the following information about certain functions:

Advisory Priority: Can revert to TA ONLY or STBY when higher priority advisories (e.g., GPWS, Windshear, etc) occur.

Altitude Climb Limit: Inhibited in accordance with aircraft performance limitations.

Descend RA: Inhibited below 1,000 feet in descent, and 1,200' in climb.

Increase Descent RA: Inhibited below 1,450'.

Resolution Advisories: Inhibited below 400' in descent and below 600' in climb. (TCAS automatically reverts to TA only)

--one might hope that with the demise of lookforshooter, the professional tone of the forum might be restored, but unfortunately he's already begun posting as nonflushinglav (strangely appropriate), and like his many other pseudonyms, has started his new posting career by agreeing with his old identity.

 

13th October 2008, 05:21   #38 (permalink)

SNS3Guppy  Join Date: Oct 2005Location: USAPosts: 1,671

I've no doubt there are many things of which you haven't heard, or with which you're not familiar...seems that most things in aviation fall into that category for you. Clearly the concept of integrated avionics is among those things...things you don't understand. Once again, despite your different screen names and claims...it only goes to show who you are, and who you aren't.

Aren't the various functions integrated on your microsoft flight simulator?

 

13th October 2008, 06:52   #39 (permalink)

SNS3Guppy  Join Date: Oct 2005Location: USAPosts: 1,671

Quote:

Certainly the challenge is out to everyone if they can show a TCAS unit coupled to Ground Prox and Radar Altimeters...

I believe I just did...having copied my information from the company Aircraft Operations Manual for our B747, that is.

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13th October 2008, 07:29

  #40 (permalink)

Spanner Turner  Join Date: May 2005Location: AustraliaPosts: 116

Quote:

Certainly the challenge is out to everyone if they can show a TCAS unit coupled to Ground Prox and Radar Altimeters...

Oh Dear, the following is from the 747-400 Maintenance Manual(my highlighting).

The dedicated components of a TCAS system consists of:• A TCAS computer• A top directional antenna• A bottom antenna,- which may be either omnidirectional or directional, dependingon the flight phase.

The TCAS system interfaces with:• The ATC system;- L and R ATC Mode S transponders,- top and bottom ATC antennae and- ATC/TCAS control panel.• Integrated display system (IDS)• Modularised avionics and warning electronics assembly(MAWEA)

The system makes use of interfaces with:• Left and Right Radio Altimeters• Ground Proximity Warning Computer (GPWC)• Landing gear module• Air/ground relays• Left and Right Distance Measuring Equipment (DME)• L and R central maintenance computer (CMC’s)• Data management unit (DMU)The TCAS II computer is a receiver/transmitter unit which containsthe processors required to determine if the path of nearby airplaneswill intersect the flight path of the TCAS equipped airplanes.

Quote:

The TCAS won't descend you into a mountain, EGPWS has priority. Yes, Pitbull, if you don't follow the RA, the coordinating aircraft will have a RA of greater magnitude, but following it is the correct response. The San Diego B727/C172 crash occurred

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when the pilot's thought they had there traffic "in sight" when the real conflict was not in their sight. If they had a TCAS II RA, decided the plane they had in sight was not really a conflict, they would have had the mid-air. Follow the RA.

I'll tell you what Galaxy. Why don't you stop putting 'head banging into wall' symbols and start actually reading posts.

Quote:

The TCAS won't descend you into a mountain, EGPWS has priority.

Agreed. You should be safe against ground contact. With a caveat: Check your MEL. Can you dispatch with the E part of EGPWS inop?

Quote:

Yes, Pitbull, if you don't follow the RA, the coordinating aircraft will have a RA of greater magnitude, but following it is the correct response.

Wrong.

Both aircraft will get their initial RA's. The only way aircraft B will get a strengthened RA is if aircraft A manoeuvres in the opposite sense. If aircraft A does not follow, or is slow to follow, or can not fully comply (e.g. makes +500 instead of +1750), then this will have no effect on the type of RA received by aircraft B.

Quote:

The San Diego B727/C172 crash occurred when the pilot's thought they had there traffic "in sight" when the real conflict was not in their sight. If they had a TCAS II RA, decided the plane they had in sight was not really a conflict, they would have had the mid-air. Follow the RA.

I'm not sure if this is directed at my post, but it's in a continuous paragraph from where you refer to me by handle, so I presume it is.

Nowhere have I suggested that RA's should be ignored if they are considered to be unnecessary. On the contrary, I've been singing the "Think its not needed? So what, follow it anyway" tune ever since TCAS was mandated, even though the 'official' guidance didn't change to that until several years later.

The pilot has the ability to be aware of multiple hazards that TCAS simply can not analyse. i.e. anything that doesn't have an altitude encoding

transponder. As such, it is possible that the act of following an RA may, in itself, be immediately hazardous. Do you dispute this? I know its a bit unpopular, but I believe that a crew might be required, from time to time, to excercise some judgement. But you know what? We could argue the toss on that one all day. The reality is that the perception of non TCAS risks depends on the type of operation. An air transport / IFR / controlled airspace / major airport pilot will have much less concern than someone who operates into places buzzing with non transponding traffic. So I suggest we just put that aside and just concentrate on the original posters issue; i.e. Performance.

The point I'm making is very simple, so I'll spell it out:

An RA may not be achievable.

Yes, TCAS has performance inhibitions. But you really need to appreciate that these are NOT comprehensive. I'd classify them as 'inhibiting the totally impossible' rather than 'guarunteeing the possible'. In addition to that, TCAS (probably: type dependant) doesn't know about engine failures / flight control malfunction. It doesn't know if you're covered in Ice.

Dispute it all you like, bottom line is that the pilots job has to be to protect the flight envelope, including if necessary not fully complying with an RA.

Don't want to take my word for it? Why not take a TCAS manufacturer's:

"The pilot must not exceed stick shaker or other stall warnings or protections when following an RA"

That's from a manufacturers manual, not just whatever sections your management pilot saw fit to put in your ops manual.

You may NOT be able to follow an RA. You MUST KNOW what to do if you can't.

pb

Last edited by Capt Pit Bull : 13th October 2008 at 11:31. Reason: finger trouble

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13th October 2008, 20:02   #42 (permalink)

SNS3Guppy  Join Date: Oct 2005Location: USAPosts: 1,671

The concept of the paragraph has been working for centuries now, and while simple, is a brilliant tool for enhancing the understandability of nearly any material.

Even material one has blindly copied verbatim, with no understanding, from another source.

 

14th October 2008, 05:23   #43 (permalink)

galaxy flyer  Join Date: Dec 2002Location: Quabog Valley, USAAge: 56Posts: 875

Capt Pit Bull

Thanks for an informative post. I learned a lot, thanks. I also learned to watch my fingers on the touchpad, I went back and looked at my post to understand your comment on "banging heads". Where they came from, I don't now.

The SAN mention was aimed at the other poster who seemed antagonistic toward following RAs as being mindless airline responses.

Thanks for the thoughtful info on TCAS. Yes, quite agree pilots must operate within the aircraft's envelope. We go to TA Only when OEI.

GF

I operate large corporate jets and did operate C-5s. Also survived a tactical military mid-air with a parachute ride, so v. interested in the subject.

 

15th October 2008, 00:30   #44 (permalink)

CJ Driver  Join Date: Aug 2003Location: ScotlandPosts: 115

I wonder why?

Galaxy Flyer - I've seen other comments similar to yours that says "we turn of TCAS RA's when we are OEI". I wonder why?

In TA only mode, the TCAS says (and I paraphrase) "Traffic! We are going to die!" and leaves it up to you to decide what to do next. If you leave the switch in RA mode, in the exactly the same aircraft in exactly the same scenario, it will say one of a small set of messages of the form (and I paraphrase again) "Descend now or we are going to die!".

Without revisiting the caveats previously posted about what performance may be available to you, and the fact that you need to exercise judgement to not turn one emergency into another - why do you prefer the "Traffic!" message to the one with some useful additional information attached? Even OEI, you can manage most of the commands (descend, maintain VS, etc), and the only one that will make you cringe is

a command to increase your rate of climb - but then you are ALWAYS going to cringe if the box just said "Traffic!".

 

15th October 2008, 02:13   #45 (permalink)

Mad (Flt) Scientist  Join Date: Sep 2002Location: La Belle ProvincePosts: 1,250

Quote:

Originally Posted by Capt Pit Bull Yes, TCAS has performance inhibitions. But you really need to appreciate that these are NOT comprehensive. I'd classify them as 'inhibiting the totally impossible' rather than 'guarunteeing the possible'. In addition to that, TCAS (probably: type dependant) doesn't know about engine failures / flight control malfunction. It doesn't know if you're covered in Ice.

Just to comment on that item. I think you'll find it to be type specific. Certainly I was earlier today reviewing a certification report for an aircraft with TCAS which did specifically address the airframe icing and WAI ON implications for performance.

 

15th October 2008, 04:45   #46 (permalink)

galaxy flyer  Join Date: Dec 2002Location: Quabog Valley, USAAge: 56Posts: 875

CJ Driver

Based I what I learned from Capt Pit Bull, I also wonder why we select TA Only. If pilots are supposed to protect the envelope, we should be responsible in the OEI case.

MfS: As the resident flight scientist, any ideas?

GF

 

15th October 2008, 08:39   #47 (permalink)

Denti  Join Date: Mar 2001Location: Somewhere down the road...Posts: 508

TA ONLY prevents the generation of coordinated RAs. So any other aircraft with TCAS treats your aircraft as if it doesn't have TCAS and thus does not expect you to do any avoiding action and consequently computes its own RAs in accordance with that. This will not compromise safety in the least but will excempt you from following an RA you might not be able to achieve in the first place.

It is an item on our OEI checklist as well, as far as i know one of those items Boeing is pretty keen on.

 

15th October 2008, 14:34   #48 (permalink)

safetypee  Join Date: Dec 2002Location: UKPosts: 510

As MFS stated many of the restrictions are type specific. IIRC the Avro RJ has engine failure detection logic, which is sent to ACAS.

 

16th October 2008, 23:21   #49 (permalink)

CJ Driver  Join Date: Aug 2003Location: ScotlandPosts: 115

How does that "not compromise safety"?

Denti - sorry but I am not convinced. In any airprox, there are many ways of solving the problem - I climb, or you climb, or I descend, or you descend, or whatever. In many encounters, the TCAS coordination means that quite mild changes - or even "no change" - can be the solution. In some of the encounters however, a guaranteed solution may only be possible with a coordinated response. Since turning off your TCAS removes those from the possible solution set, then surely you have compromised the safety net?

 

17th October 2008, 13:26   #50 (permalink)

Capt Pit Bull  Join Date: Aug 1999Location: EnglandPosts: 635

Sorry to be slow responding, kind of buried at work.

Galaxy, no probs mate. Regarding the whole TA only thing:

The reason its selected is a coordination thing that has most relevance to an encounter where manouevres in a particular sense are inhibited for one or both aircraft.

E.G. lets say 2 medium turboprop aircraft meet one another at high level. They will likely both have climb RA's performance inhibited.

Likewise a low level encounter both aircraft could be descent inhibited.

In these situations we can't have the aircraft manoeuvre in opposite senses, instead TCAS has to constrain one aircraft from doing anything with a preventative RA, whilst giving the other a corrective RA. This is an exercise in TCAS / TCAS coordination, and follows some established rules.

So, lets say aircraft A gets told to climb, and aircraft B gets told to stay level.

The strength of an RA, the time its issued, the response times, and the corrective RA thresholds are such that a single RA ought to be sufficient - if it weren't, the the system would be inadequate for protection against Non TCAS aircraft.

However, lets say that aircraft A has lost an engine,

the crew are in the early stages of working the procedures and haven't yet gone to TA only, yet are unable to get anywhere near +1750 fpm. This is going to be a bit of a shame, because there is an aircraft present - aircraft B - that has the performance required to avoid the collision, but its being specifically told not to climb.

Whereas, if aircraft A is at TA only, aircraft B will NOT coordinate its escape manoeuvre. It'll say to itself "need to manouvre - descent inhibited - I will climb". Problem solved.

In otherwords "TA only mode" frees up the other aircraft in the encounter.

Essentially, IF you are working in an 'all tcas equipped' environment, then using TA mode is a "I have priority, you get out of my way" mode.

To that end CJ driver, use of TA mode is safer if the aircraft has a situation where you know you can not respond fully or accurately to an RA. Various aircraft I have flown have had 'TA only mode' specified in several abnormal checklists relating to engine or flying control malfunctions.

Mad Flt:

Yes, lots of type dependancy in there. For sure, the TCAS may have inputs from various systems to help it know what the aircraft can and can't do. For example, on the ATR (which I was a skipper on whan TCAS was mandated) the system had inputs by making particular ice protection selections. Setting "level 2" protection (i.e. we are entering icing conditions) changed the TCAS perf inhibitions (as well as changing a bunch of other stall protection / minimum speeds etc).

Similarly in a jet, ice protection bleeds reduce performance in a quantifiable manner and presumeably quite accurate calculations can be made regarding perf inhibitions.

However, I was alluding to actual airframe ice, rather than airframe ice protection. I know a lot of folks here will be driving jets with good performance but spare a thought for the turboprop drivers who live in the teens of thousands rather than just punching through them in a couple of minutes

pb

 

19th October 2008, 01:06   #51 (permalink)

galaxy flyer  

Capt Pit Bull

Join Date: Dec 2002Location: Quabog Valley, USAAge: 56Posts: 875

Again, much obliged; now I understand not only the reason for TA ONLY, but also the importance of the selection.

Thanks much,