Flying The WAAS GPS

Presented by John D. Collins

June 13, 2014Branson Mo

Twin Cessna Flyers

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WAAS Overview

•What is WAAS?

• It stands for Wide Area Augmentation System

• Provides improved Position Accuracy including

• Horizontal to 2 meters (localizer equivalent)

• Vertical to 3 meters (allows vertical guidance)

• It also provides enhanced system integrity

• Replaces RAIM

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RNAV (GPS) Approaches More Common

As of May 1, 2014 there are almost three times the number of RNAV approaches with LPV minimums than ILS Category 1 approaches

3,404 LPV Verses 1,269 ILS Approaches

There are 13,957 approaches that use space based GPS and 6,439 approaches that use ground based facilities

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•What is a WAAS Approach?

•There are two types

• LPV – Localizer Performance with Vertical (DA)

• LP – Localizer Performance (MDA)

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• A WAAS GPS can also fly these non WAAS Approaches

• LNAV/VNAV (DA) using WAAS for the vertical

• LNAV (MDA)

• The WAAS GPS can also provide advisory vertical guidance with the following approach annunciations:

• LNAV+V (to an MDA)

• LP+V (to an MDA)

Typical WAAS Coverage

A Solar Storm

But LNAV Still Available at 100%

Entire WAAS System was down on Friday 10/21/11 for 4 hours caused by an error during a software upgrade

WAAS Integrity

•Integrity – the function that alerts the pilot if the Navigational Information cannot be relied on

•HPL - Horizontal Protection Level – 99.99999% probability that the horizontal position is contained within the limits

•VPL - Vertical Protection Level – 99.99999% probability that the vertical position is contained within the limits

HAL – Horizontal Alarm Limit is the highest value of HPL that is permitted for a given type of approach

For an LNAV or LNAV/VNAV approach, this value is 556 meters

For an LP or LPV approach, this value is 40 meters

Vertical Alarm Limit VAL – Vertical Alarm

Limit is the highest value of VPL that is permitted for a given type of approach with vertical guidance

For an LPV approach with a DH 250 feet or higher, this value is 50 meters

For an LPV approach with a DH below 250 feet to 200 feet, this value is 35 meters

On the GNS430W/530W, GTN series or G1000 how do you know if the current signal is likely to be adequate to fly a planned LPV or other approach with vertical guidance?

The GNS430W/530W, GTN series, and G1000 display the following two related values:

1. HFOM - Horizontal Figure of Merit – the 95% probability of maximum horizontal error in feet

2. VFOM - Vertical Figure of Merit – the 95% probability of maximum vertical error in feet

TIP

• When the VFOM is less than 40 feet, vertical guidance is available on all approaches including those with a 200 foot DH • When the VFOM is less than 60 feet, vertical guidance is available on any approach with LNAV+V, LP+V, L/VNAV, and an LPV as long as the DH is 250 feet or greater

•Typical values in this area are a VFOM at 20 feet.

• Tip: How do you know if an LNAV will have +V ?

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CDI Scaling for a WAAS GPS is angular and not Fixed as it is with a non WAAS GPS

LNAV CDI Scaling is angular

LNAV VTF Scaling

•GP fixed last .4 to .5 NM to threshold for LPV, 1.7 NM for LNAV/VNAV

•GP fixed beyond 6 NM +/- 492 feet FSD

TIP - Flying an Approach with an out of date database

1. AFMS must permit GPS approaches with an out of date Database (GNS430W/530W and GNS480 AFMS permit this)

2. The pilot must verify that the effective date of the approach procedure is not after the effective date of the expired database.

3. Reference AIM section 1-1-19, table 1-1-6, note 3 for IFR Approach

• It reads: “Requires current database or verification that the procedure has not been amended since the expiration of the database.”

WAAS GPS filing an alternate

• An airport with a RNAV (GPS) approach may be chosen as an alternate if the approach is designated as authorized to be used as an alternate.

• For planning purposes, the weather must be based on LNAV alternate minimums and is normally 800-2

• For approaches which require the use of an ADF or DME and the WAAS GPS needs to be used in lieu of the ADF or a DME, the approach may be used for the purposes of filing an alternate.

• If a Terminal Forecast (FA) is unavailable at the alternate airport, the area forecast (FA) and the AIRMET Sierra must be used to determine the forecast weather. This effectively requires VFR conditions.

• Does not use RAIM for integrity and therefore doesn’t need a RAIM check before flight or prior to an approach

Alternate information using AeroNav Charts

A WAAS GPS can use a RNAV (GPS) approach as an alternate if:• The AeroNav chart does not have NA, indicating the approach is not authorized as an alternate. • If there is a symbol but without the NA, then non-standard alternate minimums apply and details are found in section M.• If there is no symbol, then standard alternate minimums apply

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Jeppesen Alternate Information

The Jeppesen Airport Chart notes indicate if and what minimums are required.

When would you use a WAAS GPS to fly the LNAV/VNAV DA?

• Not often, for the most part this minima can be ignored

• On the vast majority of RNAV (GPS) approaches, if there is a LNAV/VNAV DA, there will be a lower LPV DA

• When there is a LPV DA charted, the GPS will not offer the LNAV/VNAV

• All downgrades are to LNAV without vertical guidance, there are no downgrades to LNAV/VNAV

• The LNAV/VNAV minimums are primarily intended for aircraft with a Baro VNAV system, not normally found in piston GA aircraft

RNAV Typical Minimum Relationship

LNAV/VNAV Lower than LPV

LNAV Lower than LPV or LNAV/VNAV

LNAV/VNAV How DA is affected by Obstacles

Affect of Obstacles on LPV DA

LP Approaches• Analogous to a Localizer only approach • Advisory vertical guidance only available on GNS430W/530W at Software Version 5.10 or later (LP+V)

• Will always be charted with LNAV minimums, never with an LPV or LNAV/VNAV

• Downgrade to LNAV if HPL exceeds 40 meters

• FAA plans to publish either LP or LPV at each runway

• LP will only be published if MDA is at least 20 ft lower than LNAV

• 539 LP procedures are now published

• MUST have an annunciation of LP in order to use the minimums, LNAV annunciation is not permitted to fly these minimums

LP with big improvement in MDA

Advisory Vertical Guidance

• Only available on approaches that:• LNAV minimums are highest service • the approach is straight in to a runway

• Never available when a LPV, LNAV/VNAV, or LP is downgraded

• Treating the MDA as a DA is not authorized, no sink thru allowed

• Must observe minimum, maximum, and required altitudes

• Level off at MDA to provide time to locate runway environment

• Baro Altitude is affected by temperature• Altimeter will read lower than actual with Hot temperatures• Altimeter will read higher than actual with cold temperatures• Glidepath is relatively fixed in space and independent of temperature• Error increases with altitude above Baro setting site

• No protection below the MDA from obstacles

LNAV that will have Advisory Vertical Guidance LNAV+V

Vertical guidance will not always clear step downs beyond FAF

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Dangers of using Advisory Vertical Guidance below MDA

• Absolutely no guarantee of obstacle clearance

• LP and LNAV Approaches were designed for Dive and Drive, not using a single angle all the way to the threshold

• FAA now removing Visual Descent Angle and TCH from LNAV and LP approach charts when the visual segment has obstacle penetrations in the 20 to 1 slope.

• They also now add a note, “Descent Angle NA” to affected charts and notes such as “Approach NA at Night”.

• It will take some time before all charts are updated

A dangerous example, RNAV 7 at N23+ V takes you below the ridge line

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Analyzing the approach Chart Information regarding the visual segment

Visual Segment Clear on 34 to 1

Visual Segment Clear on 20 to 1

Visual segment not clear on 20 to 1

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Flying the TAA

The Terminal Arrival Area

Pilots entering the TAA and cleared for an approach by air traffic control, are expected to proceed directly to the IAF associated with that area of the TAA at the altitude depicted, unless otherwise cleared by air traffic control.

A TAA segment is considered as a feeder route and a depicted part of the approach. Unlike an MSA, when cleared for the approach, you may descend to the segment altitude.

Tip: Make sure that the center fix bearing is used to determine TAA IAF to use.

Last assigned altitude, 6000 MSL. You receive the following clearance:

“Twin Cessna, 12345, 20 miles north of UUKAY, cleared direct UUKAY, Cleared RNAY RWY 4 Approach, Lexington”

When may you descend and to what altitude?

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What does Fly Visual Mean?

Fly Visual to Airport

• Provides relief from FAR 91.175 requirements for leaving the DA

• Missed approach climb terrain protection of 200 ft/NM is only provided at the MAP at the DA altitude.

• The flight visibility requirement in the approach must be met to leave the DA or an immediate missed approach is expected.

• This is a visual procedure, meaning that terrain clearance and flight to the runway must be accomplished by visual means. You must remain clear of any clouds.

• Descent below the DA is authorized as long as the required flight visibility is available. There is no requirement that the DA be treated as if it were an MDA until the runway is in sight. The GP may be used as long as the aircraft continuously meets the visual requirements.

• Tip: the pilot be positive that a landing can be accomplished by visual means from the MAP DA, as a missed approach from a point beyond the MAP DA means the pilot must provide for their own terrain avoidance.

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Joining the Approach

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When is flying the hold in lieu of a PT required?

Answer: If it is charted, it is required, unless:

The Hold is not permitted when:

• Cleared “Straight In” for the approach • When on radar vectors to final

• On any feeder route, segment, or TAA sector that has NoPt depicted

• When in the hold and cleared for the approach

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TIP: If in doubt, clarify the situation with the controller (91.123)

The HILPT is a “once around” procedure where the holding waypoint is crossed twice, once on entry to the hold and once inbound to the FAF.

Any circuits of the HILPT to lose altitude, etc. in addition to the “once around” or when the hold is not indicated, the pilot must obtain a clearance to fly the hold

TEST – IS a HOLD required?

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Why do I sometimes get asked to fly a hold and other times I don’t?

Answer – it depends on where you are arriving at the hold fix

Controlling the Hold In-Lieu of A procedure Turn

When the hold is the active leg annunciated by the GPS:

• When the GPS displays SUSP then the guidance will remain in the hold

• When the GPS is not displaying SUSP, then the guidance will be to sequence to the next waypoint on the approach

• Pressing OBS will toggle SUSP on and off.

Cleared direct UPBID, GPS RWY 23 Approach, It is not an available

Choice

ATC Rules for Clearance to an IF or step down fix to start an approach

• Aircraft must have filed as advanced RNAV (/G)• Altitude assigned until on a published segment of the approach• Radar monitoring required until established• Direct to IF only permitted is angle to final approach 90 degrees or less and 30 degrees or less for a step down fix.• Must advise pilot to expect clearance direct to the fix by at least 5 NM

Where does the glidepath come on

• VTF – 31 NM before the FAF when the aircraft is generally aligned with the final approach path

• Full procedure – when the FAF is the active waypoint for the current Leg

Note: sometimes this is a short leg, leaving the autopilotInsufficient time to capture the glidepath

The Miss

• Don’t be in a hurry to get missed approach navigational guidance

• Fly the miss, power up, pitch up, positive rate, Gear up

• You can wait until you have completed the initial Climb and started any required initial turn

• Verify that SUSP is annunciated, only then press OBS

TIP: Don’t be in a hurry to press OBS, wait until you see SUSP annunciated

Here is what happens if you press OBS with out firstgetting SUSP.

TIP

If you mess up and press the OBS before SUSP, the GNS400W/500W series will go into OBS mode

To undo this, use Direct-to, Direct-to, and enter, toreactivate the leg to final.

Then when SUSP comes on, you can press OBS

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Questions ?

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Supplemental Charts

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Hidden in plain view

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Hidden in plain view

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Hidden in plain view

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Hidden in plain view

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Hidden in plain view

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+Map

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+Map

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+Map

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+Map

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Parallel Track

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Parallel Track

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Parallel Track

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Parallel Track

Full RNAV approach with GPSS

With GPSS engaged (usually Heading mode on AP) fly procedure until aligned with final, then engage the approach mode

Full RNAV Approach Without GPSS 1. Use Heading or

Nav mode to navigate to IAF or IF.

2. Use Heading mode to fly procedure until aligned with final, then engage the approach mode

Command Console Lateral Guidance System

Visual Segment – Circling

• Starts 200 feet before the threshold

• Extends 10,000 feet

• Evaluated for obstacle penetration on two inclined planes• 34 to 1 – required for:

• ILS or LPV to lowest minimums• depicted on chart as gray feather if clear

• 20 to 1 - required for:• VDP to be published• Night Circling to be permitted

Visual Segment – Straight In

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•Example of LPV clear on 34 to 1

•Example of LPV Clear on 20-1 but not 34-1

•Example of LPV not clear on 20-1

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