United B772 near Seoul on Dec 31st 2012, engine shut down in flight
Last Update: February 14, 2015 / 22:59:47 GMT/Zulu time
Incident Facts
Date of incident
Dec 31, 2012
Classification
Incident
Airline
United
Flight number
UA-890
Departure
Seoul, South Korea
Destination
Tokyo Narita, Japan
Aircraft Registration
N206UA
Aircraft Type
Boeing 777-200
ICAO Type Designator
B772
The flight was cancelled.
The NTSB rated the occurrence an incident reporting that a post flight inspection revealed metal fragments in the left engine's chip detector. The South Korean Aviation and Railway Accident Investigation Board (ARAIB) opened an investigation.
South Korea's ARAIB have released their final report concluding the probable cause of the serious incident was:
The Aviation and Railway Accident Investigation Board determines the causes of this serious incident as follows:
The mechanical breakdown of the MB-7 bearing, which supports the front part of the gearbox drive gear shaft at the No. 1 engine MGB, stopped the transmission of the N2 rotor's rotational power to the MGB through the layshaft, which shut down all engine components mounted on the MGB, thereby resulting in the IFSD.
Contributing to this serious incident were as follows:
During the last engine assembly, when the MB-7 bearing was mounted on the MGB driveshaft, the PMA drive retaining nut was tightened with a less torque than that prescribed by the EM, which caused its failure to support the MB-7 bearing inner race, thereby resulting in the mechanical damage of the MB-7 bearing.
The ARAIB reported based on the captain's (52, ATPL, 20,150 hours total, 4,100 hours in command on type) testimony, that the first officer (38, ATPL, 14,782 hours total, 5,782 hours on type) was flying manually. When the aircraft climbed through FL280 the aircraft yawed to the left associated with shaking on the control columns, the left hand engine's N1 and N2 showed 20% and 0%, the IDG tripped off and the EICAS displayed ENG FAIL L. The crew worked the related checklists, attempted a restart of the engine to no avail, the captain assumed duties of pilot flying and returned the aircraft for a safe landing on runway 33L at Incheon Airport.
Immediately after the return a visual inspection of the engine revealed the N2 shaft had seized. The magnetic chip detectors in the main gearbox bearing and the engine oil tank showed substantial amount of metallic particles. An attachment bolt on the permanent magnet alternator (PMA) was fractured and was missing its head.
The left engine was removed from the airframe and sent for further analysis. The ggearbox drive gear shaft was found moved forward from its assembled position thus disengaging the drive gear shaft and layshaft. The PMA unit was removed from the main gearbox bearing, all PMA gearshaft teeth were found severly damaged and missing material. PMA rotor, stator, shaft roller bearings were in good condition however.
Main Bearing-7 rollers and cage were found liberated and distributed throughout the main gearbox case, severly deformed cage fragments were found inside the gearbox. Main Bearing-8 however remained intact.
The ARAIB analysed that during examination of the engine the break away torque of the PMA drive retaining nut was extremely lower than specified even though the breakaway torque could not be measured during disassembly. The ARAIB analysed: "It is highly likely that out of three assembly procedures above, the procedure 3 was implemented with a significantly lower torque than that prescribed by the EM, or that the procedure 3 was omitted after the retaining nut was loosened in the procedure 2." and continued: "If the torque is insufficient when the PMA drive retaining nut is assembled into the MGB drivesahft, the retaining nut's clamping force in the axial direction will reduce, which causes not only the material transfer or galling/fretting between the MGB driveshaft and the PMA drive spur gear, but also axial vibration due to the rotation of the MB-7 bearing inner race, thereby damaging the whole MB-7 bearing."
Incident Facts
Date of incident
Dec 31, 2012
Classification
Incident
Airline
United
Flight number
UA-890
Departure
Seoul, South Korea
Destination
Tokyo Narita, Japan
Aircraft Registration
N206UA
Aircraft Type
Boeing 777-200
ICAO Type Designator
B772
This article is published under license from Avherald.com. © of text by Avherald.com.
Article source
You can read 2 more free articles without a subscription.
Subscribe now and continue reading without any limits!
Read unlimited articles and receive our daily update briefing. Gain better insights into what is happening in commercial aviation safety.
Send tip
Support AeroInside by sending a small tip amount.
Related articles
United B772 near Salt Lake City on Jul 25th 2014, electrical odour on board
A United Boeing 777-200, registration N206UA performing flight UA-328 from Denver,CO to Honolulu,HI (USA) with 269 passengers and 10 crew, was…
United B772 over Atlantic on Feb 8th 2013, smoke in cockpit
A United Boeing 777-200, registration N206UA performing flight UA-935 from London Heathrow,EN (UK) to Los Angeles,CA (USA) with 182 passengers and 10…
United B738 at Fukuoka on May 10th 2024, flaps problem
A United Boeing 737-800, registration N39297 performing flight UA-166 from Fukuoka (Japan) to Guam (Guam) with 50 people on board, was climbing out…
United B763 over Atlantic on Mar 28th 2022, engine failure
A United Boeing 767-300, registration N675UA performing flight UA-134 from Newark,NJ (USA) to Zurich (Switzerland) with 123 people on board, was…
United B739 at Austin on May 5th 2024, flaps problem
A United Boeing 737-900, registration N39463 performing flight UA-381 from Washington Dulles,DC to Austin,TX (USA), was on final approach to Austin's…
United B39M at Orlando on Apr 26th 2024, runway incursion forces rejected takeoff
A United Boeing 737-9 MAX, registration N37540 performing flight UA-1929 from Newark,NJ to Orlando,FL (USA), had landed on Orlando's runway 18R and…
United B763 near Providence on Apr 22nd 2024, suspected fuel leak
A United Boeing 767-300, registration N644UA performing flight UA-108 from Washington Dulles,DC (USA) to Munich (Germany), was enroute at FL330 about…
Newest articles
Dana MD82 at Lagos on Apr 23rd 2024, runway excursion
A Dana Air McDonnell Douglas MD-82, registration 5N-BKI performing flight 9J-352 from Abuja to Lagos (Nigeria) with 83 passengers and 6 crew, landed…
LATAM Brasil A320 at Brasilia on May 13th 2024, engine shut down in flight
A LATAM Brasil Airbus A320-200, registration PR-MYI performing flight LA-3008 from Sao Paulo Congonhas,SP to Brasilia,DF (Brazil) with 106 people on…
Subscribe today
Are you researching aviation incidents? Get access to AeroInside Insights, unlimited read access and receive the daily newsletter.
Pick your plan and subscribePartner
A new way to document and demonstrate airworthiness compliance and aircraft value. Find out more.
ELITE Simulation Solutions is a leading global provider of Flight Simulation Training Devices, IFR training software as well as flight controls and related services. Find out more.
Your regulation partner, specialists in aviation safety and compliance; providing training, auditing, and consultancy services. Find out more.
AeroInside Blog
Popular aircraft
Airbus A320Boeing 737-800
Boeing 737-800 MAX
Popular airlines
American AirlinesUnited
Delta
Air Canada
Lufthansa
British Airways