Improper Assembly Of Trim Actuator Causes In-flight ... · Causes In-flight Separation of...

JULY–AUGUST 2001

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Aviation Mechanics Bulletin

Improper AssemblyOf Trim ActuatorCauses In-flight

Separation of Stabilizer

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Aviation Mechanics BulletinDedicated to the aviation mechanic whose knowledge,craftsmanship and integrity form the core of air safety.

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Improper Assembly of Trim ActuatorCauses In-flight Separation of Stabilizer ......................................................1

Maintenance Alerts ..................................................................................... 11

News & Tips ............................................................................................... 18

July–August 2001 Vol. 49 No. 4

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Improper AssemblyOf Trim ActuatorCauses In-flight

Separation of Stabilizer

All three people on board were killed when the Westwindstruck the ground out of control. The U.S. NationalTransportation Safety Board said that the flight was

the first after maintenance that includeddisassembly and reassembly of the trim-actuator unit.

FSF Editorial Staff

About 1635 local time, Dec. 12, 1999,an Israel Aircraft Industries (IAI)Westwind struck terrain near Goulds-boro, Pennsylvania, U.S. The airplanewas destroyed, and the two pilots andtheir passenger were killed.

The U.S. National TransportationSafety Board (NTSB) said, in its fi-nal report, that the probable cause ofthe accident was the “improper as-sembly of the horizontal stabilizer

trim-actuator unit by maintenancepersonnel.”

Day visual meteorological condi-tions had prevailed for the five-hour personal flight from BoeingField/King County InternationalAirport, Seattle, Washington, toTeterboro (New Jersey) Airport. Thelast recorded communication was thecrew’s acknowledgment of an airtraffic control (ATC) clearance to

2 FLIGHT SAFETY FOUNDATION • AVIATION MECHANICS BULLETIN • JULY–AUGUST 2001

descend the airplane from 18,000feet to 6,000 feet.

Witnesses said that the airplane wasin a near-vertical climb before level-ing off and beginning a series of“twists, swoops and turns.” Severalwitnesses at first believed that theywere observing aerobatic maneuvers.The airplane’s movements becamemore erratic, and then the airplanedescended “nose first, no spinning,twisting or corkscrewing,” one wit-ness said.

The airplane first struck treetops, thenthe ground.

The report said, “The accident flightwas the airplane’s first flight aftermaintenance. Work that was accom-plished during the maintenance includ-ed disassembly and reassembly of thehorizontal-stabilizer trim actuator.Examination of the actuator at the ac-cident site revealed that componentsof the actuator were separated and thatthey displayed no damage where theywould have been attached. Examina-tion of the actuator by [NTSB] re-vealed that the actuator had not beenproperly assembled in the airplane.”

During the accident investigation, asimilar actuator was assembled im-properly and was installed in an air-plane for a static ground test.

“When the actuator was run, the jack-screws of the actuator were observed

backing out of the rod-end capswithin the first few actuations of thepitch trim toward the nose-down po-sition,” the report said. “As the pitchtrim continued to be actuated towardthe nose-down position, the jack-screws became disconnected from therod-end caps, and the horizontal sta-bilizer became disconnected fromthe actuator.”

Airplane maintenance records showedthat the horizontal-jackscrew actua-tor was overhauled and returned toservice Feb. 20, 1998, and wasinstalled in the accident airplaneFeb. 26, 1998. An entry in the air-plane flight log described the in-stallation but did not mention thatthe new actuator eliminated the re-quirement for repetitive inspectionsin accordance with AirworthinessDirective (AD) 98-20-35, amend-ment 39-10802.

Subsequent entries in the flight logand in the maintenance records saidthat “A” checks were conducted Oct.9, 1998, and Dec. 10, 1999, in accor-dance with the IAI inspection guide.The flight-log entry for the Oct. 9,1998, “A” check did not mentioncompliance with the AD; no mentionwas required in the flight log.

The maintenance records said that theDec. 10, 1999, “A” check included re-moval of the left elevator, which waspainted, balanced according to themaintenance manual and reinstalled.

FLIGHT SAFETY FOUNDATION • AVIATION MECHANICS BULLETIN • JULY–AUGUST 2001 3

“Examination of the airplane’s flightlog revealed stickers that were addedto two pages of the log,” the reportsaid. “The stickers were dated Dec.10, 1999, and described work thatwas accomplished during the ‘A’check. One of the stickers stated,‘Complied with an “A” check in ac-cordance with IAI inspection guide.Complied with AD 98-20-35 Amend-ment 39-10802 on inspection of trimactuator. Actuator was replaced 3/98.This terminates the repetitive in-spections … of this AD.’”

A flight data recorder was not in-stalled, and was not required to beinstalled, in the airplane.

The cockpit voice recorder (CVR)transcript showed that the flight crewobserved indications of a problem withthe horizontal-stabilizer trim 18 min-utes before the accident, when the firstofficer said, “Elevator up … my lightjust flashed on. … There it goes again.”

Sixteen minutes later, the first offic-er said, “It’s trimming.”

The captain said, “Yeah, I left the au-topilot on intentionally.”

One minute later, the first officer said,“Elevator out of trim.”

The captain asked, “Which way?”

The CVR recorded an unidentifiedvoice saying “up” and an increase in

general cockpit noise that resembledthe sound of an increase in aircraftspeed. Twenty-three seconds later, thecaptain said, “Keep pushing.’”

No further sounds were recorded onthe CVR.

Examination of the wreckage showedthat the airplane had struck the groundabout 80-degrees nose-down withwings level. The major componentsand flight-control surfaces were foundat the accident site. The horizontal-stabilizer trim actuator was found at-tached to its support structure on theaft-main fuselage.

“The actuator was missing one of itselectric motors and did not have a dustshield surrounding the jackscrewtorque tubes,” the report said. “Clos-er examination of the actuatorrevealed that the jackscrews insidethe torque tubes were sheared. At-tached to the horizontal stabilizerfront-spar attach point were two rodends. Attached to one of the rodends was an adapter with a tie rodinstalled through it. The other adapt-er remained attached to the tierod. Examination of the rod-endadapters did not reveal any jack-screws threaded into them, and thethreads were clean and displayed novisible damage.”

The horizontal-stabilizer trim-actuator dust shield, separatedpieces of jackscrews and an electric


motor for the horizontal-stabilizertrim actuator were found in the im-pact crater. The dust shield and thepieces of the jackscrews were beneathaft portions of the airplane.

The report described their conditionas follows:

The top of the dust shield wascrushed. Holes, which weremachined at the top of thedust shield to accept a tie rod,did not display any visible dam-age, and the tie rod was not in-stalled. The separated pieces ofthe jackscrews, which werefound inside the dust shield,contained two different threadtypes. A fine thread was at themachined end, and a coarserthread was at the fractured end.The finer thread section of thejackscrews also had machinedholes through them to accept atie rod. The holes and threadswere not damaged, and the tierod was not installed.

Examinations of the rudder stopsand elevator-control stops showednormal wear. Impact damage prevent-ed a determination of the continuityof the engine controls and flight con-trols, but a laboratory analysis revealedthat both engines showed indicationsof rotation when the accident occurredand that there were no pre-impactconditions that would have interferedwith normal engine operation.

The pitch of the airplane was con-trolled by the horizontal stabilizerand two elevators. A dual-jackscrewactuator, powered by one of two re-versible motors, drove the horizontal-stabilizer leading edge up or downto make trim changes. The base ofthe jackscrew actuator was attachedby two rod-end fittings to the aftfuselage. Two torque tubes housedthe threaded jackscrews and extend-ed vertically from the jackscrew-actuator housing.

The report described the operation ofthe unit as follows:

When commanded, a gearboxinside the actuator housingwould … rotate the torquetubes, which, in turn, woulddrive the threaded jackscrewsin a forward [direction] or re-verse direction. Threaded ontothe top of the jackscrews wererod-end adapter fittings, whichalso had rod ends threaded ontop of them. The rod ends wereattached to the front spar of thehorizontal stabilizer. The jack-screws were covered by a one-piece dust shield, which movedwith them as they were extend-ed. The dust shield was in-stalled around the torque tubesto protect the threaded jack-screws from contamination.Holes were machined throughthe rod-end adapter fittings,jackscrews and the dust shield


to allow the passage of a tie rod.The tie rod’s purpose was to notonly secure the components to-gether but also to prevent thejackscrews from turning andunscrewing from the rod-endadapter fittings when the actu-ator was powered.

When the actuator was being inspect-ed or installed, the dust shield wasdesigned to be fitted over the upperends of the jackscrews so that it couldrest atop the actuator housing. Afterthe inspection or installation wascompleted, the upper ends of thejackscrews were threaded into thelower ends of the rod-end adapter fit-tings, and the dust shield was raisedabove the jackscrews. Tie rods wereinserted through each end of the dustshield, the lower ends of the rod-endadapter fittings and the upper ends ofthe jackscrews, and threaded nutswere installed at each end of the tierod. Sealant was applied around theholes of the dust shield, the tie rodand the openings where the rod-endadapter fittings extended from the topof the dust shield.

After the accident, the horizontal-stabilizer jackscrew actuator wastaken to the manufacturer, TRW Aero-nautical Systems/Lucas Aerospace.The actuator was in several pieces, andthe jackscrews were broken.

The report said that the exposedextend-limit switch cam was at the

actuation point of the microswitchand that the actuator was in the full-extend position. The retract-limitswitch cam also was in the full-extend position. Inspection revealedno damage or wear on the gearing in-side the trim actuator.

The metallurgical report from theNTSB Materials Laboratory said that,although the extend-limit switch camwas at the approximate full-extend-limit actuation point, the extend-limit microswitch was not activated.

“Additional rotation of the cam didnot activate the microswitch,” the re-port said. “[T]he extend-limit switchcam did not cause sufficient motionof the arm of the microswitch to suf-ficiently contact the switch button.”

The metallurgical inspection alsofound a crack in the housing body leftof the microswitch.

The report said that the inspectionfound a “slight, simultaneous rotationof both torque tubes.” Both torquetubes were bent forward about sixdegrees, and damage was found onthe aft side of the tubes that was “con-sistent with longitudinal sliding con-tact with other components,” thereport said.

“The lower pieces of the [fractured]jackscrews remained in each torquetube, with the fracture surfaces nearthe top surfaces of the torque tubes.


The jackscrew fracture surfaces wererough in texture and did not containcrack-arrest positions, which isconsistent with overstress separa-tions. The left jackscrew could not berotated within the torque tube byhand, but the right jackscrew was freeto rotate approximately 180 degreescounterclockwise. The fracture sur-face of the right jackscrew containeda small lip along the edge of the frac-ture at a position corresponding tothe thread-start location in the torquetube. ‘River patterns’ on the jack-screw fracture surfaces indicated thatthe fracture initiated at the aft sideof each jackscrew. The top of the lefttorque tube contained sliding de-formation adjacent to the forwardside of the fracture, which is consis-tent with contact with the jackscrewthreads.

“The right torque tube was cut fromthe remainder of the actuator. Thetorque tube and retained piece of thejackscrew were then sectioned lon-gitudinally. Rotation of the torque tubealso turned the jackscrew nut, whichwas located at the upper end of thetube. Rotation of this nut over thethreads of the jackscrew caused thejackscrew to translate into and out ofthe torque tube. After sectioning, thenut for the right jackscrew was locat-ed in its proper position inside theupper end of the right torque tube. Thethreads of the nut generally appearedundamaged with little wear. However,the thread roots in the upper threaded

portion of the nut appeared shiny withrotational scoring. Some shiny areasand rotational scoring were observedin the lower threaded portion also, butto a lesser extent.”

The metallurgical inspection alsofound that:

• The length of the centerlineholes in the jackscrews was3.38 inches (8.59 centimeters)for the left jackscrew and 3.81inches (9.68 centimeters) for theright jackscrew. Photographsfrom TRW/Lucas Aerospaceshowed that the upper pieceof the left jackscrew measuredabout 2.72 inches (6.91 centi-meters) and the upper piece of theright jackscrew measured about2.25 inches (5.72 centimeters).The IAI maintenance manual saidthat the jackscrews should havehad a stroke of 2.32 inches (5.89centimeters) limited electricallyand 2.55 inches (6.48 centime-ters) limited mechanically.

“At the mechanical retract limit,the length of jackscrew extend-ing beyond the upper surface ofthe torque tubes was approxi-mately one inch [2.54 centime-ters] in a correctly assembledactuator assembly,” the reportsaid. (At the electrical retractlimit, it was expected that slight-ly more than one inch would ex-tend beyond the upper surface ofthe torque tubes.) Adding 2.32


inches (the electrically limitedstroke) to the one-inch length ofjackscrew at the mechanical-retract limit, the minimum lengthof jackscrew extending fromthe top surface of the torque tubesat the electrically limited fullextension was approximately3.32 inches in the correctly as-sembled actuator assembly”;

• The right rod-end bearing wasbent aft about 17 degrees relativeto the rod-end adapter fitting.The left rod-end bearing had asimilar deformity next to thefracture, and the fracture surfacefeatures “were typical of over-stress separation.” The mechan-ical stop was present on the lowerend of the left rod-end adapterfitting but not on the right fitting.

The tie rod was installed throughthe rod-end adapter fittings butwas not inserted through the dustsleeve or the upper ends of thejackscrews. The tie rod was bentwhere the tie rod entered the rod-end adapters, and the exposedthreads on the tie rod were dam-aged. The inspection also foundremnants of a brown sealant anda yellow sealant on the assem-bly; in areas in which both seal-ants were observed, the brownsealant was beneath the yellowsealant; and,

• The upper end of the dust shieldwas crushed. Because the diameter

of the rod-end adapter fitting was1.5 inches (3.8 centimeters) wherethe tie rod was inserted and the topopenings of the dust shield werecrushed to one inch or less aroundthe tie-rod hole, this indicated that“the crushing damage occurredwhen the dust shield was not as-sembled around the lower endsof the rod-end adapter fittings,”the report said. “Also, the holes inthe dust shield for the tie rod werenot ovalized or fractured. Brownsealant was observed on the ex-terior of the dust shield aroundthe upper openings and the tie-rod holes, but no yellow sealantwas observed.”

When the torque tubes for the dustshield were split for further inspec-tion, thread impressions were foundthat were consistent with contact withthe jackscrews. Impressions and slid-ing marks were found that were con-sistent with a sliding contact with thetop aft edges of the torque tubes.

Investigators from NTSB and theU.S. Federal Aviation Administration(FAA) conducted separate interviewswith maintenance technicians em-ployed by the facility that maintainedthe airplane.

During the NTSB interviews, con-ducted April 11, 2000, the firstmechanic interviewed said that heremoved the access panels on thetail section of the accident airplane.


The second mechanic interviewedsaid that he had never “touched awrench to the jackscrew actuator” butthat he had conducted one hour ofresearch to check the compliance ofthe actuator AD. The third mechanicsaid that he previously had installedan actuator in the airplane and thatthe actuator had been received at themaintenance facility as a completeunit and was installed in the airplaneas a complete unit; he said that he didnot recall observing any irregularitieswith the actuator during the installa-tion and did not recall further main-tenance on the actuator after theinstallation. The fourth mechanic,who inspected the first mechanic’swork, said that he had observed thejackscrews on the actuator.

Nevertheless, the report said, “In afollow-up letter dated April 18, 2000,from the maintenance facility, themechanic stated that he might havespoken in haste when he respondedthat he had seen the jackscrews on theactuator. He stated that, in fact, hemay not have actually seen them be-cause the shield covered both.”

The maintenance facility’s follow-upletter said that the director of main-tenance (DOM) had interviewed eachemployee who had worked on theaccident airplane and that each per-son interviewed said that “at no timedid they see weights (shot bags) onthe horizontal stabilizer leading edge,nor were blocks installed. With that

information, the DOM stated that, tothe best of his personal knowledge,the maintenance facility did not per-form any maintenance to the stabiliz-er actuator during the inspectionperformed in December of 1999.”

During the FAA interviews on May5, 2000, the first mechanic said thathis task was to determine whether AD98-20-35 applied to the horizontal-stabilizer-jackscrew actuator on theaccident airplane.

“The mechanic then stated that adetermination was made that theAD did not apply to the installed ac-tuator,” the report said. “The mechan-ic performed a complete visual andoperational inspection of the actuator.When the FAA inspector asked themechanic if he had seen the threads ofthe actuator’s jackscrews, he replied‘yes.’ The FAA inspector then dis-cussed more thoroughly what the me-chanic had seen, and the mechanic wascertain that he had seen the ‘coarsethreads’ of the actuator. The mechan-ic added that he had run the trim tothe full-up (nose-down) position andinspected the actuator assembly andjackscrews. The mechanic stated thathe did not ‘touch a wrench to the ac-tuator’ and that he did not observe any-one else performing maintenance onthe actuator, or disconnecting the ac-tuator from the horizontal stabilizer.”

The second mechanic interviewedby FAA said that he was the “acting


lead” on the airplane during main-tenance and that he did not recallinspecting the actuator, did not re-call whether the actuator jackscrewswere visible and did not recall any-one else disconnecting the actuatoror performing maintenance on theactuator.

The third mechanic said that he closedinspection panels that covered the areain which the actuator was installed andthat he did not recall observing any-one working in the area where the ac-tuator was installed. He said that hedid not inspect the actuator.

The fourth mechanic told FAA thathe had removed inspection panels toallow access to the area where theactuator was installed and that he didnot recall observing anyone workingin the area. He said that he had notinspected the actuator. He did, how-ever, recall that another mechanichad applied paint to the airplane’s tailsection.

The fifth mechanic said that he couldnot recall anyone who might haveperformed maintenance on the air-plane.

The sixth mechanic said that he hadworked on the airplane and that hecould not recall removing thehorizontal-stabilizer access panels.He said that he had worked on alighting AD and had performedfinal engine runs and operational

checks before returning the airplaneto the hangar.

The report said, “He stated that heperformed functional checks on ‘allsystems’ and ran each of the trims‘stop to stop.’ Regarding the horizon-tal stabilizer trim, he believes that heused both the yoke switch and thesecondary center pedestal switch totest the trim and that it functionednormally before he returned all trimsto the ‘normal’ positions.”

An examination of maintenancerecords showed that an “A” checkwork order listed discrepancies withthe airplane and numbered them1.1 through 1.18. “Discrepancy 1.2”said, “Comply with AD 98-20-35inspection of trim actuator of the[horizontal stabilizer] per [servicebulletin] 1124-37-133.” The correc-tive action said, “C/W March 1998.This terminates the repetitive in-spection … of AD 98-20-35.” The re-port said that a mechanic and aninspector “signed off on the correc-tive action on Dec. 7, 1999.”

Billing records sent to the airplaneowner included $300.51 for labor in-volved in work on “Discrepancy 1.2.”

“On April 18, 2000, [NTSB] askedthe maintenance facility to convertthe billed amount of $300.51 into to-tal labor time,” the report said. “Thereply was that it required 7.62 hoursof labor to complete discrepancy 1.2.


“On April 20, 2000, an FAA inspectorreviewed the amount of labor hoursthat were logged by the maintenancefacility for the work order discrepan-cy 1.2. The total amount of labor was7.22 hours.”

Mandatory Service Bulletin 1124-24-133, issued Aug. 14, 1996, dis-cussed inspections of the horizontal-stabilizer trim actuator and estimatedthat, “for planning purposes only,”completion of the inspection wouldtake four hours.

Static tests were conducted May 4,2000, using an IAI Westwind equippedwith a test actuator that had been in-stalled in the same manner as thatfound in the wreckage of the accidentairplane: The tie rod was removed, thedust shield was slid down to allow ac-cess to the jackscrews, and the rod-endcaps were rotated out “to the pointwhere the tie rod could be reinsertedthrough both rod-end caps,” the reportsaid. “In this condition, the tie roddid not pass through the drilled holesof either jackscrew or dust shield. …[A]pproximately three threads of thejackscrew were engaged in the rod-end caps.”

The aircraft pitch trim was placed ina position approximating the take-off position, and a wooden block wasinstalled to prevent excessive up-ward movement of the stabilizer inthe event that the stabilizer becamedisengaged from the actuator.

The simulated flight was conductedby a pilot familiar with the routeflown by the crew of the accidentairplane. The pilot initially used thehorizontal-stabilizer trim switch onthe control wheel and later used thehorizontal-stabilizer-override controlswitch “due to the control wheelhorizontal stabilizer trim switch be-ing trimmed beyond its limits,” thereport said.

The simulated flight began with thestandard instrument departure and aclimb to 37,000 feet. When the pilotwas told to descend, the CVR tran-script and partial ATC transcripts wereused to help in assigning altitudes andATC clearances to the pilot.

The report said, “An FAA inspectorobserved the testing from the rear ofthe airplane. He was positioned on awork stand on the right side of thevertical stabilizer where he could ob-serve movement of the horizontal-stabilizer-actuator jackscrews with amirror. When the pitch trim was ac-tuated several times toward the nose-up position, the jackscrews did notrotate relative to the rod-end caps.At that point, the pitch trim beganto actuate toward the nose-down po-sition. The inspector observed thejackscrews backing out of the rod-end caps within the first few actua-tions of the pitch trim toward thenose-down position. Rotation of thetwo jackscrews was not even, and theamount of rotation varied with each


NTSB RecommendsAction to Secure

Evacuation Slides/Rafts

The U.S. National TransportationSafety Board (NTSB), citing a March17, 2001, accident involving anAirbus Industrie A320-200, hasrecommended that the U.S. FederalAviation Administration issue air-worthiness directives (ADs) to re-quire operators to ensure that thedimensions of specific parts of girtbars on overwater-equipped A319,A320 and A321 airplanes conform todesign specifications.

(A girt, the device typically usedto attach an emergency-evacuationslide/raft to an airplane, consists ofstrong fabric wrapped around a girtbar, which is installed at the doorsillof an exit.)

The NTSB recommendations re-sulted from an accident in which a

Northwest Airlines A320-200 over-ran the runway during a rejectedtakeoff from Detroit (Michigan,U.S.) Metropolitan Wayne CountyAirport. The airplane was damagedsubstantially. Three of the 151 peo-ple in the airplane received minorinjuries.

After the airplane was stopped in mudbeyond the departure end of the run-way, an emergency evacuation wasperformed. During the evacuation, theemergency evacuation slide/raft atdoor 2L separated from the airplaneand fell to the ground when the doorwas opened.

The accident airplane, like otheroverwater-equipped A319, A320 andA321 airplanes, had a slide/raft ateach floor-level emergency exit.The slide/raft is attached to the doorby a packboard. The slide/raft in-cludes a fabric girt and a telescopicgirt bar, which enables the slide/raftpack to be removed from one exit’s

MAINTENANCE ALERTS

actuation of the trim. As the pitchtrim continued to be actuated towardthe nose-down position, the jack-screws became disconnected fromthe rod-end caps and the horizontalstabilizer became disconnected fromthe actuator.”♦

[FSF editorial note: This article, ex-cept where specifically noted, isbased on U.S. National Transporta-tion Safety Board Aircraft AccidentBrief, accident no. NYC00MA048.The 274-page report contains dia-grams and photographs.]


floor fittings for deployment outsideanother door, if necessary.

“When the door is ‘armed,’ the girtbar is attached to the floor fittings onthe doorsill so that when the door isopened, the girt bar will pull on theslide/raft and initiate its deployment,”NTSB said. “When a door is ‘dis-armed’ and opened, the girt bar re-mains attached to and moves with thedoor, thereby preventing the slide/raftfrom deploying.

“The telescopic end of the girt bar islocked in the extended position by aspring-loaded trigger. … Squeezing thetrigger causes the trigger-locking mech-anism to retract within the telescopicend of the girt bar, allowing it to slideinto the stationary portion of the girtbar and shorten the overall length ofthe girt bar so that the slide-raft can beremoved from the floor fittings.”

The exposed end of the trigger-locking mechanism overlaps and con-tacts the stationary portion of the girtbar to prevent the girt bar from re-tracting. During the accident investi-gation, NTSB determined that thelikelihood of a secure engagementbetween the stationary portion of thegirt bar and the trigger-locking mech-anism is reduced if the amount ofchamfer (bevel) on the stationary por-tion of the girt bar is increased.

An inspection of the telescopic girtbar at exit door 2L of the accident

airplane showed that its chamfer was0.77 millimeter (0.03 inch) on thehorizontal surface and 0.93 millime-ter (0.04 inch) on the vertical surface,instead of 0.50 millimeter (0.02 inch),as required by the design.

“When the 2L door was opened in the‘armed’ mode, the force of the dooropening apparently allowed the tele-scopic end of the girt bar to retractwithin the stationary portion of thegirt bar,” NTSB said. “This retractionallowed the aft end of the girt bar toslip from its floor fitting and rotateforward. This movement and theweight of the slide/raft pulled theforward end of the girt bar from itsfloor fitting and caused the uninflat-ed slide/raft pack to separate com-pletely from the airplane and fall tothe ground.”

Although the other two slides/rafts onthe airplane deployed normally, girtbars on those two doors also werechamfered improperly. NTSB saidthat meant there was potential forslide-raft separations at those doorsand that, “if this had occurred, threeof the four floor-level emergency ex-its on the accident airplane wouldhave been unusable by passengersduring the evacuation.”

During the investigation, Airbus In-dustrie said that two other slide/raftseparations — on an A321 and anA320 — had been attributed to im-properly chamfered girt bars. Both


separations — one on June 3, 1999,and the other on April 1, 2001 — in-volved airplanes operated by AirMacau, and both occurred duringroutine maintenance tests.

A March 1999 revision of theA319/A320 Airbus MaintenanceManual (AMM) included a new item,subtask 52-10-00-220-077, “Checkof the Adjustment of the Girt Bar,”to be conducted every 36 months toensure that the length of the tele-scopic girt bar can be shortened onlyby depressing the trigger.

The check had not been conducted onthe accident airplane. When accidentinvestigators tried to retract the tele-scopic end of the 2L girt bar, they suc-ceeded every time; when they tried toretract the telescopic ends of girt barson the other two slides/rafts, some oftheir attempts were successful.

“This indicates that the results fromconducting the test specified in theAMM are likely unreliable,” NTSBsaid.

On April 11, 2001, Airbus Industrieissued All Operators Telex (AOT)A320-52A1110, which recommend-ed that operators of all overwater-equipped A319, A320 and A321airplanes conduct a “one-time testfor the non-retraction of the tele-scopic girt bar without manually ac-tivating the trigger.” The AOT saidthat the test should be conducted

within 500 flight hours after opera-tors received the AOT. The AOT alsosaid that, if the girt bar retracts with-out manually activating the trigger,it must be replaced or modified be-fore the next flight.

Eight days after the AOT was issued,the 2L slide/raft of an A320 operatedby FTI, a German charter company,detached from its floor fittings dur-ing an operational test, fell to theground and inflated. Airbus Industriepersonnel said that the chamfer of thegirt bar was slightly outside designrequirements and that a requiredseven-degree cutback at the end ofthe trigger-locking mechanism wasnot present. The operator had con-ducted the AOT test the day beforeand had found no anomalies.

NTSB also said that the test outlinedin the AOT may not detect improper-ly chamfered girt bars and trigger-locking mechanisms with impropercutbacks. The accident airplane, theAir Macau airplanes and the FTI air-plane had manually chamfered girtbars; NTSB said that A319, A320and A321 airplanes with machine-chamfered girt bars could experiencesimilar problems.

Therefore, NTSB asked FAA to is-sue an emergency AD to require op-erators of overwater-equipped A319,A320 and A321 airplanes with man-ually chamfered girt bars to accom-plish the following:


• “Ensure that the dimensions ofthe trigger-locking mechanismand the stationary portion of thegirt bars conform to the designspecifications;

• “Perform a reliable functionaltest to demonstrate the properengagement of manually cham-fered girt bars under realisticdoor-opening conditions; and,

• “Repair or replace any girt barsthat do not meet the dimension-al requirements or do not pass thefunctional test, before the air-planes are returned to service.”

NTSB said that FAA also should is-sue an AD to require operators ofA319, A320 and A321 airplanes withmachine-chamfered girt bars to im-plement the same actions “by the nextscheduled maintenance activity.”

Improper MaintenanceCited in Wheel

Separations

The U.S. National TransportationSafety Board (NTSB) has cited im-proper action by maintenance person-nel in two 1999 incidents in whichwheel assemblies separated fromairplanes during takeoff.

The first incident involved a McDon-nell Douglas DC-9-51, from which aleft-outboard main wheel and tire

assembly separated during takeoffOct. 14, 1999, from Chicago (Illinois,U.S.) Midway Airport. The assemblystruck an airport perimeter wall, dis-lodging two panels from the wall.Two panels and the tire-and-wheelassembly then struck two vehicles ona nearby road.

The airplane received minor damageand was flown to the destination air-port for a normal landing. None ofthe 109 people in the airplane wasinjured. The driver of one vehicle wastaken to a hospital for observation; theother driver and two passengers werenot injured.

NTSB said that the probable causeof the accident was “the landinggear’s wheel separation due to the im-proper installation of the wheel bycompany maintenance personnelusing incomplete maintenance stepsand the maintenance steps not listedin the manufacturer’s manual.”

The separated tire was found, still in-flated and with the axle nut correctlyin place. NTSB said that the anti-skidtransducer adapter was “loosened andbacked out 4 1/2 turns” and in contactwith the back of the axle nut, althoughthe design required space between theadapter and the axle nut.

The tire had been changed Oct. 1,1999, in accordance with the ma-nufacturer’s 32-40-01 maintenancemanual.


“The manual was reviewed, and itssteps did not caution mechanics tocheck for the proper depth of theadapter,” NTSB said.

After the incident, the manufacturerissued temporary service bulletinsthat said that maintenance personnelshould “check the depth [space] di-mension of the transducer adapterwith reference to the applicabletechnical data.”

In the second incident, the right-main-landing-gear inboard wheelseparated from a Boeing 737-347during takeoff Dec. 24, 1999, fromSalt Lake City (Utah, U.S.) Interna-tional Airport. The flight crew con-tinued the takeoff and returned fora normal landing. The airplane re-ceived minor damage; none of the133 people in the airplane wasinjured.

The separated tire-and-wheel as-sembly struck and damaged runwaylighting.

Investigation showed that a Boeing757 main-wheel bearing had beeninstalled on the incident airplaneduring build-up in the operator’smaintenance facilities. The B-737main-wheel inner bearing (part no.596) has a diameter of 3.375 inches(8.573 centimeters); the B-757 main-wheel inner bearing (part no. 594)has a diameter of 3.750 inches (9.525centimeters).

NTSB said that the probable cause ofthe incident was “improper assemblyof the wheel.”

NTSB said that five other incidentsof incorrect bearing installation hadbeen reported to The Boeing Co.

Chafing in Flexible HoseBlamed for Oil Leak

The pilot of a Piper PA-31 Navajoobserved oil on the right-cockpit floorduring a flight in Canada. The oil-pressure gauge for the no. 2 engineindicated that oil pressure was lowand was continuing to decrease.

An inspection by maintenancepersonnel showed that the replace-ment flexible-hose assembly (partno. 23745-14) to the no. 2 engineoil-pressure gauge had been chafedthrough behind the instrument panelwhere the hose was bundled. The re-placement hose was not bundled be-cause technicians believed that, bysupporting the hose outside a bundle,chafing would be less likely and in-spection would be easier.

Loose ClipCited in Failure ofHydraulic Pump

An Avions de Transport Regional(ATR) 72-202 was being taxied fortakeoff from an airport in England


when the flight crew experiencedwhat they believed was an elevator-pitch disconnect, accompanied by thefailure of the green-system hydraulicpump, which provides power for thelanding gear and brakes. The airplanewas taxied back to the gate.

Inspection of the green-system hy-draulic pump showed that the elec-trical supply loom had chafed againstthe right-elevator control cable (partno. 13S27381310-000/A00) and hadworn away the insulation on thehydraulic-pump power-supply ca-bles. As a result, the conductorsshort-circuited and tripped the circuitbreaker for the hydraulic-pump elec-trical supply.

The incident report by the U.K.Air Accidents Investigation Branch(AAIB) said, “The associated localizedthermal damage to the elevator controlcable had caused it to break. The heatgenerated by the shorting/arcing hadalso initiated a small fire in the adja-cent insulation blanket, but this self-extinguished without damaging anyother adjacent systems or components.”

The electrical cable loom was retainedby a number of cable clips; one clipwas too large and could not retain theloom securely. As a result, the electri-cal supply cables contacted the right-elevator control cable. The illustratedparts catalog (IPC) showed that the size–16 clip (part no. NSA 935807-20)was correct to specification.

Maintenance personnel replacedthe damaged section of the power-supply cable and both elevator con-trol cables in the affected area. Theyalso wrapped the loom with electri-cal tape. The electrical tape was in-tended to increase the diameter of theloom so that the loom could be heldmore securely by the clip.

After the incident, other ATR 72 air-planes in the United Kingdom wereinspected to determine the size andorientation of the clip at the same po-sition on the cable. Two other air-planes had clips at the same position,and both were a smaller size thanspecified in the IPC.

“It was believed that these had been in-stalled at manufacture,” the report said.

The manufacturer issued ATR all op-erators message (AOM) 72/01/001and mandatory service bulletin (SB)ATR72-92-1004 (applicable to ATR72-100, ATR 72-200 and ATR 72-210airplanes) on Jan. 26, 2001, to requireinspection, replacement of damagedlooms or cables, installation of a size–16 clip and reorientation of the clipfor increased clearance from eleva-tor control cables.

Engine CowlingSeparates During

Takeoff

An Avions de Transport RegionalATR 42-300 was at 19,000 feet on a


flight from England to France when acabin crewmember told the flightcrew that a passenger had observed apanel missing from the no. 1 engine.The flight crew then observed that partof the no. 1 engine outboard cowl doorhad broken off. They returned to thedeparture airport, where they observedthe broken part of the cowl door andsmaller pieces of debris near the run-way threshold.

Investigation showed that a mainte-nance technician had conducted aroutine weekly check of the airplanethe day before the incident. The checkhad been conducted in darkness butin a lighted area on the apron in frontof the terminal building. The main-tenance technician said that he be-lieved that, after the inspection, hehad followed his customary practiceof releasing the cowl-door stay, sup-porting the door while descending astepladder until he could “allow thedoor to hinge closed past his head”and then fastening the latches.

The morning of the incident, the cap-tain conducted a preflight, walk-around inspection in darkness, usingartificial light.

The incident report by the U.K.Air Accidents Investigation Branch(AAIB) said, “He believed that all

engine-bay doors had been flush withthe surrounding panels although, be-cause of their height above ground,he was not able to confirm that thelatches were engaged.”

Investigation showed that the left doorof the no. 1 engine bay “had not beenrestrained by its latches and had hingedopen under the influence of the pro-peller slipstream when engine powerhad been increased at the start of thetakeoff run. … The mostly likely causeof the failure … appeared to be thatthe door had inadvertently not beenlatched following the weekly checkand that this had not been noticedduring the preflight [walk-around]inspection. … Both the check and theinspection were conducted in the hoursof darkness, with the aircraft posi-tioned such that the door would havebeen shadowed from the apron lights.”

AAIB recommended that the opera-tor review procedures to ensure thatall airplane access doors are proper-ly latched before flight and repeatedan earlier recommendation thatthe European Joint Aviation Authori-ties and the U.S. Federal AviationAdministration consider — for futureaircraft certification — a requirementfor warning systems to alert flightcrews to the presence of unlatchedaccess panels or doors.♦


Cleaning SystemsRemove ContaminantsFrom Hydraulic Oils

Kleentek electrostatic oil-cleaningsystems remove tars, varnishes andother insoluble contaminants fromhydraulic oil systems, said the man-ufacturer, Kleentek, a division ofUnited Air Specialists.

The systems use electrostatic princi-ples to draw contaminants from oilin machines and trap the contami-nants on the surface of the Kleentekcollector. The systems help reduce theneed for oil changes and system downtime, said the manufacturer.

For more information: Kleentek,4440 Creek Road, Cincinnati, OH45242 U.S. Telephone: (888) 281-4888 (U.S.) or +1 (513) 891-0400.

Clamp-on MetersMeasure

Electrical Current

Three AEMC clamp-on meters mea-sure alternating current (AC) amper-age to 1,000 amperes, AC and directcurrent (DC) voltage to 600 volts,ohms, continuity and frequency,said the manufacturer. The clamp-onmeters also have a diode-test func-tion.

The Model 514 provides AC andDC current measurements to 1,000amperes. The Model 511 providesaverage sensing; Model 512 andModel 514 provide true RMS (rootmean square, which indicates theeffective voltage of an AC signal)measurements.

For more information: AEMC In-struments, 200 Foxborough Blvd.,Foxborough, MA 02035-2872 U.S.Telephone: (800) 343-1391 (U.S.) or+1 (508) 698-2115.

Software ProvidesImproved Servicing

Of EmergencyBattery Packs

New software for Christie’s CASP/2500 battery-maintenance system hasmade servicing aircraft emergencybattery packs more efficient, said the

NEWS & TIPS

Clamp-on Electrical Meters


manufacturer, a division of MarathonPower Technologies.

The TD-750 software includes adata-logging system for instantdata capture and documentation. Thesoftware maintains a record of servicetasks performed, eliminating the needfor manual documentation, and al-lows for easy calibration and testingof emergency battery packs, said themanufacturer.

signal processing with detaileddynamic echo information that pre-viously was available only with ana-log cathode ray tube displays, said themanufacturer.

The USN 60 has a capability of 250kilohertz to 25 megahertz, with eightselectable frequency ranges; a high-resolution (640 pixels by 480 pixels)color liquid-crystal display; a 60-hertzupdate rate; and a single-shot mea-surement technique for a fast re-sponse from immersion testing andfrom critical weld testing, said themanufacturer.

For more information: KrautkramerBranson, 50 Industrial Park Road,Lewistown, PA 17044 U.S. Tele-phone: +1 (717) 242-0327.

Cotton Mounted PointsRetain Geometry of

Machined Parts

Non-woven cotton-fiber mountedpoints can deburr and finish precision-machined parts without changingtheir geometry, said the manufacturer,Rex-Cut Products.

Rex-Cut Mounted Points are avail-able in bullet shapes and cylindricalshapes. Their non-woven cotton fi-ber and abrasive grains of aluminumoxide or silicon carbide providesmooth, controlled grinding, and

Battery-maintenanceSystem Software

For more information: MarathonPower Technologies Co., 8301 Impe-rial Drive, Waco, TX 76712 U.S.Telephone: +1 (254) 776-0650.

Flaw Detector ProvidesDetailed Information,

Digital SignalProcessing

Krautkramer’s USN 60 UltrasonicFlaw Detector combines digital


they reveal fresh abrasives as theygrind. They are available in very-fine-grain sizes to coarse-grain siz-es; in soft bonds, medium bonds orhard bonds; and with shanks of 0.25inch (6.35 millimeters) and 0.13 inch(3.30 millimeters). They are suitablefor titanium, stainless steel andhighly alloyed parts, said the manu-facturer.

Attachments FunctionAs Part of Vacuum

Lifting SystemCustom vacuum attachments areavailable for use on systems withcompressed-air balancers as part ofa non-weight-sensitive vacuum lift-ing system, said the manufacturer,Anver Corp.

Anver Custom Vacuum Attachmentsfor air balancers bolt on to compressedair balancers to create a non-weight-sensitive vacuum lifting system that willnot float, the manufacturer said. Theattachments are based upon standardcomponents and are interchangeable.

For more information: Franck Ver-nooy, Anver Corp., 36 ParmenterRoad, Hudson, MA 01749 U.S.Telephone: (800) 654-3500 (U.S.) or+1 (978) 568-0221.♦

For more information: Rex-CutProducts, P.O. Box 2109, FallRiver, MA 02722 U.S. Telephone:(800) 225-8182 (U.S.) or +1 (508)678-1985. Vacuum Attachment

Mounted Points

Want more information about Flight Safety Foundation?

Contact Ann Hill, director, membership and development,by e-mail: [email protected] or by telephone: +1 (703) 739-6700, ext. 105.

Visit our World Wide Web site at http://www.flightsafety.org

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• Benefit from safety servicesincluding audits and completesystem appraisals.

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