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A SERVICE PUBLICATION OFLOCKHEED AERONAUTICALSYSTEMS COMPANY

EditorCharles I. Gale

Art DirectorCathy E. Howard

Vol. 20, No. 3, July-September 1993

CONTENTS

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3

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13

Focal Point0. J. Smith, ManagerReliability & MaintainabilityEngineering Department

Plugs and Covers forYour HerculesKeep foreign materials wherethey belong-outside your aircraft.

Generator Control Unit TruthTable MonitoringLED fault codes and BIT capabilitiesprovide insight into GCU operation.

Emergency Locator TransmitterRetrofit ModificationNew retrofit kits make this valuablesafety feature available to mostHercules operators.

Covers: Capt Jeff Renner and Capt PeteSchweyher of 435th Airlift Wing weremembers of the first Hercules crews toairdrop relief supplies into eastern Bosniaduring operation Provide Promise earlierthis year. Pictured here at the 1993 Inter-national Airlift Rodeo, they representedtheir unit at the world’s most prestigiousairlift competition. Our back cover showsa general view of the many C-130s thatparticipated in the event. Photos by JuliusAlexander.

Focal

0. J. Smith

R M Engineering:Key to Continuous Improvement

In this issue of Service News you will findseveral articles on new and improved items for theHercules aircraft. Notice the diversity of the subjects:from plugs and covers to new electrical powergeneration components. These are representative ofthe ongoing effort to improve all aspects of theaircraft, and the Reliability, Maintainability Engi-neering Department is involved in all of them.

Each item of our support equipment is continual-ly reviewed for adequacy and obsolescence, and thedesigns and materials are improved as needed. Theupdated plugs and covers featured in this issue arejust a few examples of the results of our commitment

to expand and enhance our entire line of products. Others include a new engineperformance calculator, an improved deicer truck, an engine scavenge oil test kit,and a cargo ramp handling dolly. The goal of all of this effort is simple: to serveLockheed customers better.

But support equipment is only a small part of the Reliability and MaintainabilityEngineering story. We constantly monitor aircraft systems performance in Herculesairlrfters throughout the world to pinpoint adverse trends. This allows us to providethe operational and maintenance data that forms the basis of engineering changeproposals to improve these systems. We also furnish data to facilitate trade studieswhich select the best of several possible system candidates. Once the system isselected, the design is monitored for ease of maintenance, servicing, andinspection. Analyses are conducted to establish inspection and maintenanceprocedures, training needs, and support equipment requirements.

The technical data used to support the aircraft are also subject to this improve-ment process. New and expanded system troubleshooting procedures (faultisolation) are being developed. These procedures are constructed to not onlyprovide positive identification of malfunctioning parts, but also wiring faults downto the single wire between identifiable test points.

This process of improving the Hercules aircraft through the application ofreliability and maintainability engineering techniques is continuous. Through thisprocess, you are assured of owning one of the most supportable airlifters in theworld.

ManagerReliability and MaintainabilityEngineering Department

J. L. GAFFNEY - DIRECTOR

FIELD SUPPLY TECHNICAL RM&S CUSTOMERSUPPORT SUPPORT PUBLICATIONS DESIGN TRAINING

C. A. McLeish J. L. Bailey A. G. Hunt H. D. Hall S. S. Clark

Keeping a Clean Machine:

Plugs and CoversYour

Herculesby Roy H. Webber,

Product Support Engineer Specialist Sr.Reliability and Maintainability

Engineering Department

D ust, dirt. sand, birds, insects, and other foreignobjects have no business in any kind of mechanical

equipment, much less a high-tech product like a modernairplane. If allowed to get into the critical systems of theHercules airlifter, these materials can cause all sorts ofdamage, and significantly increase maintenance costs.

It is for this reason that every new Hercules issupplied with a set of plugs and covers designed to keepsuch potential contaminants exactly where they be-long-outside the airplane. Unfortunately, these valu-able protective devices are often among the first items togo astray once an airplane enters service. Some get lostor are damaged by rough handling, while others gradu-ally become unusable because of the effects of exposureto sunlight and harsh weather conditions.

Replacement plugs and covers are readily availablethrough the normal spares channels, and they are wellworth their cost in terms of increased service life for thecritical aircraft components that they protect. Partnumbers and a brief description of each item are givenin the appropriate technical manuals.

There have been, however, a number of changesand improvements in this area in recent years. Thismakes a more detailed look at this type of equipmentworthwhile. Note that all of the items described in thediscussion below are included in the basic set of protec-tive plugs and covers that come with each new airplane.except where indicated. The part numbers given areapplicable tocurrent-model Hercules aircraft. Operatorsof older Hercules shouldconsult the authorized technicalmanuals for their aircraft or contact Lockheed FieldService for assistance before ordering.

Lockheed SERVICE NEWS V20N3 3

APU Exhaust

All recent Hercules models are equipped with anauxiliary power unit (APU), which has an exhaust ducton the left side of the aircraft. When the APU is notrunning, this duct should be plugged with the PN33 12755-I 1 APU Exhaust Cover Assembly (Figure 1).

Several product improvement modifications havebeen carried out on this part lately. Originally madefrom epoxy-fiberglass, in the past the cover has some-times been difficult to insert because of its rigidity. Lastyear, the part was redesigned and new tooling producedto make a plug that can be inserted more deeply into theduct. Four additional saw slots were also added to thesides to improve flexibility.

This new part proved much easier to install, and didnot have a tendency to pop out after insertion as wassometimes reported with the old part. Further studieshave since been undertaken and we are now using apolycarbonate plastic material to fabricate this plug.This material provides even greater flexibility andreduced manufacturing costs.

APU Cooling Air Ports

Three small air scoops and outlets are located on theunderside of the aircraft below the APU. These ductscan be plugged with the PN 3402904-l APU CoolingAir Port Plug Assembly (Figure 2). This assembly is notincluded as part of the standard plug set provided withnew aircraft. If your Hercules is equipped with skis, thePN 3402409-3 assembly must be used.

These APU cooling air plugs are formed from redthermoplastic sheeting, and have numerous slots whichprovide flexibility during insertion.

Propeller Spinner and Engine Nacelle Cover

The PN 404100-l Spinner and Nacelle Cover(shown above) is a protective device designed for use inparticularly harsh environments. It is made of weatherand sunlight-resistant vinyl fabric.

Engine Exhaust Pipe

The engine exhaust pipe area can be protected withthe PN 3402251-3 Engine Tail Pipe Shield (Figure 3).This plug is fabricated from a red epoxy-fiberglassmaterial that is designed to withstand the elevatedexhaust pipe temperatures which could be present whenthe plug is inserted. A metal handle is attached to theplug for easy insertion and removal.

Lockheed is currently changing the material to ahigh-temperature polycarbonate plastic for this applica-tion. This change will provide a more flexible partwhich will be easier to install, and at the same timereduce manufacturing costs. The part number remainsthe same.

Engine Air Intake Ducts

Engine air inlets should be protected with the PN3403246-l Engine Inlet Plug (Figure 4). Older versionsof this cover were fabricated from a rigid red thermo-plastic sheet material that bears the trade name Kydex.Over the years, some problems have been experiencedwith plugs fabricated with this material. These includelooseness of fit, which sometimes caused the plugs tofall out, and physical changes resulting from many hoursof exposure to direct sunlight and the atmosphere. Plugsthus affected became brittle and tended to break ifdropped.

4

Currently, Lockheed manufactures engine inletplugs from a lightweight but rigid pink polyethylenefoam that is contoured and edge-tapered to fit the inletduct. Some early problems with this material, such aspoor durability due to inadequate sunlight resistancewere resolved last year when a new process was intro-duced in which the polyethylene foam is coated with atough, flexible polymer. The bright red color of thepolymer also improves the appearance of the product.

Proper handling and use of engine inlet plugs isessential if they are to be able to perform their intendedfunction. To fit the plug into the engine intake ductproperly, always take the time to get up on a ladderwhere you can reach the inlet easily; then install the plugand seat it by tapping gently around its edges. This willhelp avoid any possibility of the plug popping out on itsown and becoming lost.

Note that a convenient rope handle is attached toeach plug to permit easy removal. Be sure to make useof this handle when removing engine inlet plugs. Pullingstraight out on the rope handle will do the job quicklyand easily.

A red “remove before flight” streamer is alsofastened to the engine inlet plug. The streamer is at-tached by a nylon cord, and intended to serve as a visualreminder that the plug is in place. Do nor attempt toremove engine inlet plugs by pulling on these streamers.The streamer cord is not designed to be used in thismanner and is likely to break after a few tries. Thiswould result in the streamer being separated from theplug, which would defeat its entire purpose.

Air Conditioning Inlet and Exhaust

In current models of the Hercules aircraft, fourpolymer-coated rigid polyethylene foam plugs are usedto protect the air conditioning ducts. Last year, the taperof these parts was changed for a better fit into the ducts.Very little force is required to seat these new plugs.Also, the same red polymer coating used on engine inletplugs is now being applied to the air conditioning plugs.

The cargo compartment air conditioning systemuses plug set PN 3403258-l (Figure 5). This set consistsof two plugs: an intake plug and an exhaust plug, tiedtogether with a polyethylene rope.

Extra caution should be used when inserting theround exhaust plug into the cargo compartment exhaustduct. This is a round duct that extends downward fromthe wheel well, but it is cut at the end to a shape thatapproximately conforms to the exterior shape of thewheel well panels. Because the duct is not squared off atthe end, there is a tendency for the plug to be insertedat an angle, with the bottom tilted outward.

Lockheed SERVICE NEWS VZON3

Then, since the plug does not seem to insert easily,extra force is used to push the plug into the duct. Thiscan result in a large tear in the plug surface, caused bythe sharp, specially contoured edge of the metal duct.

To avoid such damage, it is very important to insertthis plug in a vertical position which matches the ductangle as shown above. The sides of the plug are slightlytapered, and very little force is needed to seat it correct-ly. When properly seated, the bottom flat surface isalmost parallel to the ground.

The flight station air conditioning system uses thePN 3403257-I plug set (Figure 6). This set also consistsof two plugs tied together with a polyethylene rope.

There are, in addition, two other special plug setsavailable for the air conditioning inlet and exhaust ducts.These are used to adapt the aircraft inlet ducts to anexternal air conditioning cart. This permits positivelocking of the cart’s large-diameter flexible hose to the

aircraft, allowing cooling air to be introduced into theairplane’s duct distribution system during maintenanceor ground operations. These adapters (not pictured) arenot included with the regular plugs at the time of aircraftdelivery, but they can be ordered separately. The cargocompartment air conditioner plug adapter assembly isPN 3312700. The flight station air conditioner plugadapter assembly is PN 33 11849.

Pitot Tubes

Pitot tubes need shielding too. They should beprotected by the PN 3338306-l Pitot Tube Cover(Figure 7). This cover is made of cotton duck fabric,with a small cord sewed into the end to allow it to betied to the pitot tube for greater security.

All-Around Protection

Because of its size and the wide diversity of mis-sions it is called upon to perform. the typical Herculesaircraft leads a rugged, outdoors existence. Even inrelatively moderate climates, the aircraft is routinelyexposed to the kinds of environmental conditions thatwould quickly ruin most other types of precision ma-chinery.

Fortunately, the Hercules is built to take it. With alittle help from you to protect in its intakes, exhausts,and instrumentation

your aircraft.

Figure 1 APU exhaust cover assembly.

Lockheed SERVICE NEWS V20N3

Figure 2. APU cooling air port assembly.

5

Prouctile plu~:; and co•ers ure u.>ed to protect the airpla11e from neather and foreig11

debris when rhe 111rp/111re fa cm the gro1111d .

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F1.rJl»'6 5. Cargo compartment air condlnontng sysft1n1 plug $~t.

locldl"'d SERVICE "'E\'/$ V20N3 7

023 5314 • - -- -

Flgwe 7. Phot tube covers

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Flgwe 6. Flight stalion a.r condulonlno system plug $8\.

by Norm Stevens, Training SpecialistCustomer Training Systems Department

Generator Control Unit0 0 0 0

Truth TableMon i to r ing

H ercules aircraft beginning with Lockheed serialnumber LAC 527 1 are equipped with new genera-

tor control units (GCUs), PN 697856-l. IndividualGCUs replace the ensemble of components-voltageregulator, generator control or protection panel, andfrequency-sensitive relay-thatwerepreviouslyrequiredto control each of the aircraft’s engine-driven generatorsand the APU generator.

GCU Capabilities - an Overview

The new GCUs provide an advanced, solid-stategenerator control system that offers greater reliabilityand lower maintenance costs, while helping to ensurethat the aircraft subsystems are supplied with high-quality electrical power that meets the steady-state andvoltage transient requirements of MIL-STD-704D.

These units are specifically designed to providecontrol and monitoring of the 40150 KVA generatorsinstalled on the engines and APU of the Herculesaircraft. They will operate automatically with either theBendix or the Leland (GE) generator.

Each GCU monitors the permanent magnet genera-tor (PMG) input from the main generator to determinethe type of regulation to provide. If the PMG voltage is30 VDC, the generator is a Bendix unit and the regulatorfor the Bendix generator PMG is selected. If the PMGvoltage is 108 VAC, the generator is a Leland unit andthe regulator for this type PMG is selected.

This selection is done automatically and requires noaction on the part of the aircraft operator’s maintenancepersonnel. With this feature, it is possible to operate an

8 Lockheed SERVICE NEWS V2ON3

aircraft with a mix of these generator types withouthaving to match the generators to a particular voltageregulator. In addition, the units provide under- andovervoltage monitoring, under- and overfrequencymonitoring, differential fault protection, and generatorcontactor control. GCU LED status lights are alsoprovided to simplify system troubleshooting.

The GCUs provide continuous monitoring of thegenerator three-phase AC output and control thecontactors which tie the generators to the aircraft loads.If any of the monitored parameters are outside limits,the affected generator contactor will be deenergized andthe generator OUT light will illuminate. In most cases,the generator exciter field will also be deenergized.

A general introduction to the features of this newequipment was published in Lockheed Service NewsVolume 19, No. 2 (April-June 1992). In the presentarticle, we will be primarily concerned with interpretingthe LED truth table readout of the GCU’s systemmonitoring and built-in-test (BIT) capabilities.

System Monitoring

The GCU’s system monitoring capabilities areprovided by the unit’s microprocessor and internalmemory. Random-access memory (RAM) providesdigital storage capabilities for the LED display, systemfault detection circuitry, and latching circuit logic.

When the engines and APU are not operating, all ofthe RAM in the GCU is cleared each time the aircraft orGCU power is cycled from on to off. Any failure codesthat may be present are typically purged from memorywhen power is removed from the unit. When the GCUis powered up again, the GCU conducts its normalpower-on system checks unaffected by previouslydetected faults.

During normal engine and generator operation.PMG input, generator voltage and frequency,contactor current limitation, and the feeder-faultsensing circuits are continually checked for properoperation, Should any fault be detected, the generatorsystem will be deactivated, and an appropriate fault codewill be loaded into memory and displayed on the GCU’sLED status lights.

The operator may then elect to cycle the generatorswitch on the flight station overhead electrical controlpanel from ON to OFF/RESET and back to ON torestore the system. This will clear most failure codes, ifthe fault has been corrected. However, feeder fault.previous feeder fault, or previous BIT failures cannot becleared by cycling the generator control switch. Thesefaults will activate a latching circuit that prevents thesystem from powering up until the appropriate correc-tive action is taken.

System Fault Responses

Most generator system failures that occur duringnormal operation will result in a power-down commandbeing issued by the GCU. At the same time, a flag is setin the system fault portion of memory. The power-downcommand will cause the generator line contactor to bedeenergized and the generator OUT light on the over-head electrical control panel in the flight station toilluminate. Typically, the generator exciter field willalso be deenergized. In all cases, however, an errorcode will be displayed on the GCU’s LED display toindicate the cause of the failure.

It should be standard maintenance procedure tocheck the LED truth table before using the generatorcontrol switch to reset the system during GCU trouble-shooting. Similarly, flight engineers should be encour-aged to check the failure codes on the GCU prior toselecting OFF/RESET with the generator controlswitch. This will provide more complete informationabout the nature of any problems that may exist, andsimplify the job of the technician who is tasked withcorrecting the discrepancy later on the ground.

Clearing Failure Codes

In most cases where failures codes are displayed onthe LED truth table, clearing them is simply a matter ofremoving the fault that caused the code to be displayedand then cycling the generator control switch to theOFF/RESET position and back to ON again.

There are certain codes, however, namely thoseresulting from the detection of a feeder fault, previousfeeder fault, or previous built-in test (BIT) failure, thatrepresent potentially serious generator system problems.Such codes cannot be cleared by resetting the generatorcontrol switch or cycling the DC power to the GCU.These codes activate a latching circuit that prevents thesystem from powering up until suitable remedial actionis taken. What is required in these cases is a “cold”shutdown of the affected generator control system.

In a cold shutdown, both DC input power andpermanent magnet generator (PMG) voltage to the GCUare reduced to zero. This will remove the failure code,unlatch the latching circuit, and-providing the neces-sary repairs have been made-restore the system tonormal operation. A cold shutdown can be accomplishedin either of the following ways:

I. If the affected engine is running, shut it down andcycle the GCU DC power circuit breaker.

2. If the engine is not running, cycle the GCU DCcircuit breaker off and back on, or cycle the aircraftDC power off and then back on.

Lockheed SERVICE NEWS V20N3 9

BIT Capability

The BIT designed into the GCU allows the operatorto verify that the GCU’s internal built-in test circuits areperforming properly. Three modules are checked duringthe BIT. These are the digital board, power board, andchassis components. Any failures detected during theBIT will cause an appropriate LED failure code to bedisplayed.

The BIT can be initiated anytime the GCU ispowered and the generator control switch is in the ONposition. BIT can be accomplished whether the genera-tor is operating or not, and whether it is on line or offline. BIT it is somewhat more inclusive when thegenerator is off line, however.

Note that the BIT is performed only on request. Onepush of the guarded pushbutton switch located justabove the truth table on the GCU initiates the test. Thefour LED indicators will illuminate for approximately 5seconds and then extinguish if the GCU passes all theinternal BIT checks. If a failure is detected, one or moreof the LEDs will remain illuminated. The operator canthen determine the specific failure by referring to thetruth table legend on the face of the GCU.

If the generator control switch is cycled to OFF/RESET and then back to ON with a BIT failure codedisplayed and the generator is not operating (no PMGvoltage applied to the GCU), a previous BIT failurecode will be displayed. Power-up will then be deniedbecause the latch set circuit has been activated. A coldshutdown will be required to reactivate the affectedgenerator.

However, if the generator is operating (PMGvoltage available to the GCU), the presence of a failurecode which is displayed as the result of a BIT requestwill not normally keep the generator from coming online. Nor will such a code take the generator off line ifthe BIT is performed with the generator control switchin the ON position.

If the BIT pushbutton is pressed a second time underthese circumstances, the BIT will run again (all fourLEDs will illuminate). At the end of the test, the origi-nal failure code will be redisplayed if the fault continuesto exist. No code will be displayed if the problem hasbeen corrected or was transient in nature.

BIT With Displayed System Failure Codes

Each time the GCU’s BIT is initiated, it is a newtest. A displayed system failure code will not be carriedover to a following test. As soon as the pushbutton ispressed to start the BIT, the LED display will becleared. Note, however, that only the display memoryis erased during this test.

It is for this reason that the BIT should not beinitiated after a system failure has occurred until theoperator has attempted to reset the system by placing thegenerator control switch in the OFF/RESET positionand then back to ON. If a failure has been detected andthe BIT is run before OFF/RESET is selected, thefailure code will be erased from display memory anddisappear from the LED truth table.

However, if the BIT detects an internal GCUfailure, the fault code identifying the failed module willbe shown on the LED display. If no internal faults aredetected, the display will go blank. To reset, the genera-tor control switch must be cycled to OFF/RESET andthen back to ON.

Similarly, running the BIT also leaves the latchingcircuit state unaffected. We have already noted thatwhen a feeder fault, previous feeder fault, or previousBIT failure code is displayed, the latching circuit is setto prevent the generator exciter field from beingreenergized. During the BIT, the latching circuit ischecked, but if it is found already latched, it will berelatched at the end of the test.

As we have seen, however, the BIT will clear theoriginal failure code from display memory. Unless anew failure is detected, the display will remain blank. Acold restart is necessary to restore normal operation.

GCU Failure Code Summary

0 3 NO FAULTS

During normal aircraft operation, all four LEDs remainextinguished. This indicates that no failures have beendetected by the GCU and the system is operatingproperly.

It should be kept in mind that certain failure condi-tions can result in a blank truth table display. If theisolated DC bus voltage input to pin W of the GCUconnector is less than 18 VDC, the GCU goes into ahold mode, waiting for the input voltage to rise above 18VDC. No LED status is shown when this condition ispresent. The same is true when the GCU internal fusehas been blown because of incorrect generator selection(see below).

3 0 0 OVERVOLTAGEWhen AC voltage on one or more phases exceeds aninverse time curve of 5 volt-seconds above 130 VAC, upto a maximum of 190 VAC, the GCU will initiate apower-down command. The line contactor will thenopen, the generator exciter field will be deenergized,and the generator OUT light will illuminate. Thegenerator can be reset by placing the generator controlswitch to OFF/RESET and then back to ON. If theovervoltage condition recurs, the GCU will trip again.

10 Lockheed SERVICE NEWS V2ON3

UNDERVOLTAGE

If voltage on one or more phases drops to 95 VAC orbelow for more than4 seconds, a power-down commandwill be issued: the line contactor will open, the genera-tor exciter field will be deenergized, and the generatorOUT light will illuminate. The generator can be reset byplacing the generator control switch toOFF/RESET andthen back to ON. If the undervoltage condition recurs,the GCU will trip again.

Note that if one or more of the three-phase sensinginputs to the GCU is open or shorted, the GCU assumesthat an undervoltage condition has occurred. This willcause an undervoltage failure code to be displayed.

0 0 UNDERFREQUENCY

If the frequency drops below 365 Hertz, the linecontactor will open, the generator OUT light will illumi-nate, and the underfrequency code will be displayed onthe truth table LEDs. When frequency rises above 375Hertz again, the line contactor will close, the generatorOUT light will go out, and the underfrequency code onthe LED display will be extinguished. Note that theunderfrequency condition is normal when the engine isoperating in low-speed ground idle.

0 l 0 0 OVERFREQUENCY

If the frequency exceeds 440 Hertz, the line contactorwill open, the generator OUT light will illuminate, andthe overfrequency code will be displayed on the truthtable LEDs. When the frequency drops below 430Hertz, the line contactor will close, the generator OUTlight will go out, and the overfrequency code on theLED display will be extinguished.

It should be kept in mind that since frequency is afunction of engine rpm, and the engines that power theHercules aircraft are controlled at a constant speed,overfrequency codes are extremely rare.

0 0 FEEDER FAULT

Whenever a feeder fault is detected, the GCU willinitiate a power-down command and the generator OUTlight will illuminate. The generator exciter field will bedeenergized, and the line contactor will also bedeenergized. The feeder fault condition also causes thelatch set circuit to be set, which will prevent the GCUfrom being reset.

In this situation, the fault code is loaded into systemRAM and shown on the GCU’s display table. IfOFF/RESET is selected with the generator controlswitch when the feeder fault condition is present, theGCU’s LED truth table will go blank and remain thatway until the generator control switch is selected back tothe ON position. The truth table will then display theprevious feeder fault code. The presence of this codedenies power-up and the latch circuit remains set.

Lockheed SERVICE NEWS V2ON3 I1

When a feeder fault has been detected, it requires acold shutdown-removing all PMG voltage and DCpower from the GCU-to clear system memory andreset the latch set circuit. The system will then be readyto resume normal operation. However, the condition thatcaused the fault must be corrected before the generatoris reactivated and connected to the bus again; otherwise,the power-down will recur.

0 0 PREVIOUS FEEDER FAULT

When a feeder fault has been detected and the generatordeenergized, the LED display on the GCU will go blankif the operator selects OFF/RESET with the generatorcontrol switch. If the generator control switch is thenselected back to ON, a previous feeder fault code will beshown on the truth table. With this code displayed, thelatch set logic keeps the exciter field circuit open, andthe generator will remain off line. A cold restart isnecessary to restore normal operation,

0 CONTACTOR CURRENT LIMIT

Display of this code indicates that the current limits tothe generator line contactor or bus tie contactor havebeen exceeded. This condition can sometimes be tracedto coil failures.

The GCU normal current rating (excluding initialpull-in current) for the generator line contactor and bustie contactors is 3 amps continuous. Whenever morethan 3.6 amps (continuous) is exceeded, the GCU goesinto a pull-back mode. This will cause the micro-proces-sor to initiate power-down, deenergizing the generatorline contactor and bus tie contactor for the affectedgenerator. The contactor current limit fault code willalso be displayed. To reset, select OFF/RESET with thegenerator control switch.

0 0 0 INCORRECT GENERATOR SELECTED

This indicates disagreement between the system firm-ware and the hardware of the GCU’s logic circuitry.The presence of this failure code will deny power-up.

If the GCU selects the Bendix generator when infact a Leland generator is installed, high PMG voltagewill be established on the GCU’s PMG line. However,an internal protective (fail-safe) circuit limits the PMGDC voltage to 70 volts, When the high voltage isdetected, the field relay and line contactor control relayopen, which isolates the GCU from the generatorsystem. This fail-safe system is independent of themicroprocessor, and will automatically reset if theinternal logic reverts to a correct generator selection.

In cases where the GCU selects a Leland generatorwhen in fact a Bendix generator is installed, an internalfuse will be blown because of excessive current draw onthe transformer-rectifier unit of the GCU. This occursbecause DC voltage is being applied to the primary

winding of the transformer. If the internal fuse hasblown, the GCU must be replaced.

0 0 GENERATOR SELECT TIMEOUT

When this code is displayed, the cause is PMG outputoscillation or pulsation, or internal GCU failure. Thecomputer has timed out while trying to decide on thegenerator type (Leland or Bendix). This failure alsodenies power-up. To reset, select OFF/RESET on thegenerator control switch.

INTERRUPT CAPACITY EXCEEDED

This failure is caused by noise in the frequency inputfrom the generator. The GCU senses the A-phase outputof the generator and converts the sine wave to a squarewave, which is used in determining the frequency. If thesquare wave contains excessive noise, the interruptcapacity of the microprocessor will be exceeded.

This condition is interpreted as a failure, and theGCU will initiate power-down. To reset, selectOFF/RESET on the generator control switch.

0 l PREVIOUS BIT FAILURE

This is the result of a previous BIT failure involvingone of the 3 modules of the GCU: digital board, powerboard, or chassis (see below). A BIT was accomplishedand an LED error code for one of the above moduleswas displayed.

The previous BIT failure code can only be generatedwhen the generator is not operating (no PMG voltageapplied to the GCU), and the operator cycles the genera-tor control switch to OFF/RESET and then back to ON.The specific failure is not shown; only the fact that theGCU has failed a previous BIT.

In this condition, power-up is denied because thelatch set circuit has been set. A cold shutdown is neces-sary to restore the system to normal operation.

l DIGITAL BOARD FAILURE

This failure consists of the digital unit’s inability toconvert discrete and analog signals to digital signals.The circuits checked are generator selection, feederfault, and feeder fault latch. If a problem is detectedduring generator operation, the failure code will bedisplayed, but in most cases the system will continue tofunction.

If the generator is not operating and a digital boardfailure is found during a BIT request, the fault code willbe displayed and power-up will be denied. Cycling thegenerator control switch at this point will cause the LEDdisplay to change to the previous BIT failure code.Power-up is denied in this condition because the latchset circuit has been set.

12

0 POWER BOARD FAILURE

This fault consists of an AC- sensing, regulator, orfrequency-sensing failure. If the generator is operatingwhen this fault is detected, the failure code will bedisplayed, but in most cases the system will continue tooperate.

If the generator is not operating and a power boardfailure is discovered in the course of running the BIT,the fault code will be displayed and power-up will bedenied. Cycling the generator control switch at thispoint will cause the LED display to change to the previ-ous BIT failure code. Power-up is denied in this condi-tion because the latch set circuit has been set.

CHASSIS FAILURE

This code indicates a failure of the field relay, or the and/or +28-volt power supply. When this

failure is detected during generator operation, the GCUtruth table will display the fault code, but the system willusually continue to function.

If a chassis failure is detected during a BIT requestwith the generator not running, the fault code will bedisplayed and power-up will be denied. Cycling thegenerator control switch at this point will cause the LEDdisplay to change to the previous BIT failure code.Power-up is denied in this condition because the latchset circuit has been set.

BIT IN PROCESS

In this case, the BIT pushbutton has been pressed, andthe GCU is in the self-check mode for approximately 5seconds. At the end of the test, all will extinguishif the test has been passed. Activation of the BIT will notinterrupt the normal operation of the generator, genera-tor line contactor, or bus tie contactor. Note that theillumination of all four also serves as a bulbcheck.

The author and Service News wish to express theirappreciation to Gary Kuzkin of Leland ElectrosystemsInc., for his very generous and valuable assistance in thepreparation of this article.

Lockheed SERVICE NEWS V20N3

Emergency Locator TransmitterR E T R O F I T M O D I F I C A T I O N . .

by D. C. Harrison Senior Design Engineer

Advanced Design Division . . . . --- S ince the entry of the Hercules airlifter into service, cal Systems Company has taken stews “to make- this

operators worldwide have employed it as a multi- valuable emergency locator feature available to opera-mission platform in a full spectrum of environmental, tors of all Hercules aircraft. A retrofit kit has beengeographical, and political situations. The Hercules developed which allows an ELT-similar to those now’..continues to meet the challenges imposed by the per- being installed on new Hercules.aircraft to be added to . . formance of difficult and dangerous airlift operations, as existing aircraft with a minimum of downtime and well as conducting a wide variety of special missions.

. .e x p e n s e .

It does not appear likely that the mission require- The Emergency Locator. Transmitter Retrofit Kit ments of the future will be very different. Hercules includes an emergency locator transmitter; an externallyaircrews will continue to find themselves engaged in mounted antenna, and a remote contro1 switch installa-relief efforts or other support roles in areas where their tion. The system is battery-powered and has no interfacelabors are complicated by difficult terrain, treacherous with the aircraft’s electrical system. In addition to all ofweather, political unrest, or a combination of these the required wiring and hardware, each kit is suppliedfactors. with a copy of Hercules Service Bulletin 82-679, which

contains the instructions necessary for installing andNot surprisingly, some of these assignments could testing the kit components.

contribute to an increase in safety risk. Because theelement of safety risk can never be completely eliminat- System Configurationed from any operation, every technological advance thatcan help enhance survivability in the event of an aircraft Major components contained in the ELT installationmishap deserves serious consideration. are the whip antenna and its mounting assembly, the

transmitter with mounting rack, the remote-controlOne such technological advance is the new emer- toggle switch, and the wiring required to interconnect

gency locator transmitter (ELT) currently being incorpo- the system’s components. The locations of these compo-rated as standard equipment on most new C-130H nents are shown in Figure 1.aircraft built for the U.S. military. Lockheed Aeronauti-

TRANSMITTER AND SUPPORT RACK(INSIDE CARGO BAY)

ANTENNA AND DOUBLER

TE CONTROL SWITCH INSTALLATION

MAIN INSTRUMENT PANEL)

Figure 7. ELT component configuration on C-130.

Lockheed SERVICE NEWS V2ON3 13

The transmitter and support rackassembly mount overhead in the aftfuselage (Figure 2). The support rackpositions the transmitter to face thedirection of flight. This location pro-vides easy access for installation andmaintenance without interfering withcargo loading.

COAXIAL CABLE RACK ASSEMBLYTO ANTENNA

The whip antenna mounts on theaft fuselage dorsal fin, with a doublerbetween the antenna and dorsal skin(Figure 3). The doubler plate pro-vides a template for marking themounting hole pattern on the skin. Inaddition to holes needed to mount theantenna, another hole is drilled at FS930 to accommodate a pressurefeedthrough connector. Screws, lockwashers, and nuts are used to securethe antenna assembly.

EMERGENCY LOCATORWIRES TO REMOTE TRANSMITTERCONTROL SWITCH

Any convenient location in theflight station may be selected forinstallation of the remote controlswitch. Two wires are installed alongexisting fuselage wire routing pathsfrom the flight station to the transmit-ter (Figure 4). A coaxial cable con-nects the transmitter and antennathrough the pressure feedthrough atFS 930. All of the necessary wireharness clamps and hardware are alsoprovided.

VIEW LOOKING INBOARD - LH SIDE

Figure 2. Transmitter and support rack.

System Operation

The ELT is an entirely self-con-tained, emergency transmitter that ispowered by alkaline batteries. It oper-ates at frequencies of 12 1.5 MHz and243.0 MHz. The ELT is designed tostart operating automatically if animpact of sufficient magnitude occurs.

ANTENNAMOUNT ASSEMB

DOUBLER(INSTALLED OVER

EXISTING FASTENERS ’

DORSAL FIN

ASSEMBLYSIDE VIEW

Figure 3. Antenna installation.

ANTENNAMAIN INSTRUMENT EMERGENCY LOCATORPANEL DISCONNECT (FS 927 WL 310 TOP CL)

ON/TEST \I n COAXIAL CABLEREMOTE

\

ANTENNA

FS 245 RH(APPROX) REMOTE PRESSURE FEEDTHROUGH

(FS 930 APPROX TOP CL)REMOTE CONTROL SWITCH

(CO-PILOT’S MAININSTRUMENT PANEL)

TRANSMITTEREMERGENCY LOCATOR

(FS 825 WL 270 BL 8L)

Figure 4. ELT system diagram.

14 Lockheed SERVICE NEWS V20N3

For automatic operation, the ELT ON/OFF/AUTOswitch located on the transmitter (Figure 5) is placed inthe AUTO position. The switch must also be in thisposition to allow the transmitter to be operated from theremote control location.

r

ANTENNA

REMOTE

Figure 5. Transmitter front panel.

The remote control switch (Figure 6) must likewisebe set in its AUTO position to permit normal systemoperation. This is the proper setting during flight, andallows impact forces to trigger transmitter operationautomatically. The unit will activate when a 5G to 7Gacceleration force of 11 to 16 milliseconds is appliedalong the line-of-flight axis.

The unit can also be activated manually. In general,the ELT will be operated manually only when anemergency landing is imminent. Note that when theELT is transmitting, the signals will interfere with com-munications on 121.5 MHz and 243.0 MHz. If at allpossible, Mayday calls for assistance should therefore bemade with the normal VHF communications transmittertuned to 121.5 MHz before the ELT operation is trig-gered.

The ELT is activated manually by placing theremote control switch in the ON/TEST position. TheELT will then begin broadcasting signals immediately.Note that the remote control switch is a toggle switchwhich must be pulled toward the operator before posi-tioning. Alternatively, ELT operation can be initiated bysetting the ON/OFF/AUTO switch on the ELT unititself to the ON position.

In case the ELT is activated by an exceptionallyhard landing, it can be deactivated and reset to theautomatic mode condition by setting the remote controlswitch to the ON/TEST position, then back to AUTO.

System Test Procedures

To test the system, the appropriate aircraft trans-ceiver is set to 121.5 MHz or 243.0 MHz and theremote control switch placed in the ON/TEST position.The ELT should begin transmitting. After a l-second

PI

ELTREMOTE CONTROL

ON TEST

TOIANUALLY

JLL TO ON

TO RESET

PULL TOON THEN

TO AUTO

AUTO

Figure 6. Remote control switch.

test period, the switch is placed at AUTO. If the ELTdoes not transmit while the remote control switch is inthe ON/TEST position, the transmitter must be checkedto verify that it is operational and that the switch on theELT unit is correctly positioned at AUTO.

A Proven Choice

The ELT installation is recognized as an effectiveand valuable modification, and the retrofit kit devel-oped for its installation ensures a quick and convenientmodification. Please contact the following for furtherinformation about the Emergency Locator TransmitterKit. and refer to PN 3341900-l:

Technical/ Engineering Information:

Lockheed Aeronautical Systems CompanyAirlift Derivative ProgramsDept. 93-20Marietta, GA 30063-0492; USATelephone 404-494-2793Fax 404-494-7784

Proposal/Procurement Information:

Lockheed Aeronautical Systems CompanyCustomer Supply Business ManagementDept. 65-l 1Marietta, GA 30063-0577; USATelephone: 404-494-7529 (U.S. government)404-494-2 116 (commercial or international)

Service News Serialization

With the present issue, an adjustment has been madeto bring the publication date into synchronization with thedate shown in the magazine. This issue is beingdesignated Vol. 20, No. 3. and the three previous issuenumbers, Vol. 19, No. 4, Vol. 20. No. I, and Vol. 20,No. 2, will be skipped.

-Ed.

Lockheed SERVICE NEWS V2ON3 15

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l\1in11i11-g ll'ith rlie Jiercu.les

Service News Congratulates the 1993 International Airlift Rodeo \\'inners:

Best Overall - 440lh Airlift Wiog, AFRES B<:Sl-l.!.!lefnatio.oal Tean>- l'ortugal. FA!'