# NTSB ANC99IA025: Boeing 747-100, N481EV, Fairbanks, AK, January 19, 1999 - Type: NTSB incident investigation - Classification: Incident · No injuries · Incident investigation · Final report - Date: January 19, 1999, 03:26 local (07:26 UTC) - Place: Fairbanks, AK - Coordinates: 64.900413, -148.160476 (estimated) - Nearby events: https://openairdocs.org/map.md?lat=64.9004&lon=-148.1605&mi=10 - Phase of flight: [Landing](https://openairdocs.org/ntsb-phases/550) (OpenAirDocs' grouping) - Highest injury: No injuries - Injuries: 4 uninjured - Status: Completed, report June 21, 2000 - Report: Approved by Office Director - NTSB office: Alaska Regional Office - NTSB case key (mKey): 45704 - NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=ANC99IA025 - NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/45704/pdf - Page: https://openairdocs.org/ntsb/ANC99IA025 ## Probable cause The improper overhaul of the thrust reverser pneumatic drive unit, and the subsequent failure of the thrust reverser actuator. Factors associated with the incident were the inadequate quality assurance procedures by the overhaul company. ## Sequence of events In NTSB's coding before 2008 (https://www.ntsb.gov/GILS/Documents/codman.pdf). - Airframe/component/system failure/malfunction, landing - roll - thrust reverser,actuator - failure,total (cause) - maintenance,overhaul - improper, other maintenance personnel (cause) - inadequate surveillance,inadequate procedure, company/operator mgmt (contributing factor) - weather condition - temperature extremes (contributing factor) - weather condition - temperature,low (contributing factor) - Fire, taxi - from landing - exhaust system,exhaust cone/tailpipe(jet engine) - fire ## Analysis After landing, the number four engine thrust reverser remained deployed. A tailpipe fire occurred, with no reported cockpit indications of either the fire or the extended reverser. Ground personnel notified the crew of the fire, and the engine was shut down. A teardown inspection revealed that the thrust reverser pneumatic drive unit (PDU) had been incorrectly assembled at the previous overhaul, 113 hours and 26 cycles prior to failure. The required stroke of the PDU interlock mechanism is 1.318 to 1.326 inches. At disassembly, the stroke was measured to be 1.230 inches. This stroke is required to allow the gear change mechanism to fully shift (from extend, to retract). The PDU retract pawl fracture surfaces were indicative of overstress. The lowest ambient surface temperature the airplane had been exposed to at the various airports during the 26 landing cycles had been -13 degrees Fahrenheit. The surface temperature during the failure of the PDU was -27 degrees Fahrenheit. ## Factual narrative On January 19, 1999, at 0326 Alaska standard time (AST), a Boeing 747-100 airplane, N481EV, sustained minor damage when a fire occurred in the number four engine while taxiing from landing at the Fairbanks International Airport, Fairbanks, Alaska. The crew of three, and the one jumpseat passenger, were not injured. The airplane was operated by Evergreen International Airlines, Inc., of McMinnville, Oregon. The flight was operated under 14 CFR Part 121 as a supplemental air carrier international cargo flight. The flight departed Chitose, Japan, at 2159 AST, and an IFR flight plan was filed. Visual meteorological condition prevailed at the time of the incident. Interviews of the flight crew and ground personnel, conducted by the NTSB investigator-in-charge (IIC), and FAA inspectors, revealed that ground personnel observed flames coming from the number four engine after the airplane had landed, and that they notified the airport control tower via radio. Control tower personnel relayed this information to the cockpit crew. The crew then shut down the number four engine and activated the on-board fire suppression equipment. During an interview on January 20, the captain told the NTSB IIC that there were no cockpit indications of fire except for a rapidly rising exhuast gas temperature (EGT), nor any cockpit indications of the thrust reverser remaining deployed. Postincident inspection revealed soot located outside the engine cowling, and the number four thrust reverser pneumatic drive unit (PDU) was found in the thrust reverser deployed position. Internal inspection of the engine revealed no overtemperature damage, or fuel soot streaking through the turbine section. All observed evidence indicated that the fire was confined to the tailpipe area of the engine. Facsimile correspondence between Pratt and Whitney product support engineers and the operator on January 21, indicated that if the thrust reverser remained deployed during taxi, an engine surge with rising EGT condition and a tailpipe fire could result in the JT9D-7A engine. The engine fire indicating system in a JT9D-7A engine is a heat sensitive coil inside the engine cowling. The PDU, which was received in the stowed position, was disassembled under the guidance of an NTSB investigator at the AlliedSignal facility in Anniston, Alabama, on February 24, 1999. The PDU was found to have several assembly discrepancies as compared to component maintenance manual (CMM) 78-31-63, Rev 19. Some of the discrepancies were: shims were installed on the wrong side of the slinger, the oil seal was installed backwards, and shimming spring washers to the feedback gears were installed incorrectly. The stroke of the interlock mechanism was measured to be 1.230 inches. The specified value is 1.318 to 1.326 inches. According to AlliedSignal, this stroke measurement is required to allow the gear change mechanism to fully shift (from extend, to retract). Damage was evident to the gear change mechanism outer ratchet ring, and locking pawl assembly, to include a broken pawl. All parties present on February 24 agreed that the broken pawl would result in binding in the retract direction. Other discrepancies in the buildup are noted in the teardown report (attached) submitted by AlliedSignal. The NTSB investigator who attended the inspection on February 24 told the NTSB IIC that he concurred with all factual observations noted on that day. The PDU was overhauled 113 hours and 26 cycles prior to failure of the retract pawl on the gear change mechanism. The broken retract pawl and gears were inspected at the NTSB metallurgical laboratory and all fracture surfaces were indicative of overstress. The geographic locations of operation for the previous 26 cycles were all warm weather locations, except for three. On January 7, and January 13, the airplane landed at Anchorage, Alaska, where the temperature was -1 degree Fahrenheit. On January 13, the airplane also landed at Khabarovsk, Russia, where the temperature was -13 degrees Fahrenheit. The ambient surface temperature at Fairbanks when the incident occurred was -27 degrees Fahrenheit. An interview by the NTSB IIC with the chief inspector for the overhaul company revealed that other PDUs assembled by the same mechanic were recalled, and disassembled for inspection. No similar discrepancies were found with these PDUs. At the time of assembly of the failed PDU, the company had a policy of quality assurance spot checks at various steps during PDU buildup, as specified in the manufacturer's overhaul manual. ## Aircraft - Registration: [N481EV](https://openairdocs.org/deregistered/N481EV-2010-08-25), registration cancelled 2010-08-25, S/N 19896, built 1970 (OpenAirDocs) - Reported make and model: Boeing 747-100 - Registry model: [Boeing 747-132](https://openairdocs.org/model/boeing-747-132) (registry code 1384882) (OpenAirDocs) - Registry engine: [Pratt & Whitney JT9D-3A](https://openairdocs.org/engine/pratt-whitney-jt9d-3a) (registry code 52050, turbo-fan) (OpenAirDocs) - Category: Airplane - Serial number: 19896 - Airframe hours: 26359 - Engines: P&W JT9D-7A 46150 lbs thrust turbo fan - Damage: Minor damage - Fire: On-Ground - Flight: Part 121 - Operator: Evergreen Int'L Airlines, Inc. - Registered owner: First Security Bank, Na - Airworthiness certificate: Standard, Transport - Last inspection: Continuous airworthiness, January 6, 1999, 113 hours before - Departed: RJCC, CHITOSE - Destination: FAI - Flight plan: IFR - Airport: FAI, Fairbanks Int'L Airport, runway 1L, 11,800 × 150 ft, asphalt ## Flight crew As NTSB recorded them. NTSB leaves out names. - Pilot; age 53; airline transport, flight engineer; airplane ratings: single-engine land, multi-engine land; instrument ratings: airplane; medical: class 1, valid medical--w/ waivers/lim; seat: left; flight hours: 23,000 total, 3,000 in this make and model, 22,000 as pilot in command, 168 in the last 90 days, 33 in the last 30 days, 11 in the last 24 hours ## Weather - Conditions: Visual (VMC), Night/dark - Wind: calm - Visibility: 3 statute miles - Lowest ceiling: none - Temperature: -27 °F ## FAA reports on this event (1) The FAA's own accident and incident reports, matched to the aircraft by N-number and date (OpenAirDocs). - [Incident 19990119004649I](https://openairdocs.org/incident/19990119004649I), Jan 19, 1999: Boeing 747132, Fairbanks, AK, Minor damage. (.19) On January 19, 1999, at 0326 Alaska standard time (ast), a Boeing 747-100 airplane, N481EV, sustained minor damage when a fire occurred in the number… From the NTSB's public API. Aircraft are matched to registry aircraft by N-number and event date, checked against the reported serial number, make and model; the registry's history has gaps, so older matches can be wrong. Compare the reported make and model. --- OpenAirDocs.org is an independent research project of [Contrail Labs](https://contraillabs.com/). It is not affiliated with the FAA or the NTSB. Source documents are U.S. government works in the public domain.