UA52 - Incident: United B763 near Shannon on Apr 7th 2022

A United Boeing 767-300, registration N670UA performing flight UA-52 from Washington Dulles,DC (USA) to Zurich (Switzerland) with 116 passengers and 10 crew, was enroute at FL360 about 80nm south of Shannon (Ireland) when the crew reported they had shut down the left hand engine (PW4060) and decided to divert to Shannon. The aircraft landed safely on Shannon's runway 24 about 25 minutes later. The aircraft vacated the runway and was taxiing towards the apron when emergency services reported the left hand landing gear had caught fire, the aircraft stopped while fire fighters extinguished the fire. The aircraft was subsequently towed to the terminal where the passengers disembarked.

On Feb 29th 2024 the Irish AAIU released their final report concluding the probable causes of the serious incident were:

Probable Cause

Migration of the No. 4 bearing Magnetic Chip Detector probe from its housing on the oil pump assembly on the No. 1 engine, followed by a loss of oil through the valve in the Magnetic Chip Detector housing, which remained partially open, due either to debris in the valve or as a result of a partially migrated probe.

Contributory Causes

- The MCD probe was not in the installed and locked position.

- The Operator’s MCD maintenance procedures were not followed when maintenance was performed on the MCD probe prior to the occurrence flight.

- There was no red paint in the alignment grooves on the grip of the MCD probe or on the MCD housing; this was permitted by the Operator’s MCD inspection procedures.

- The presence of debris within the MCD housing.

- The MCD probe’s o-ring (primary seal) and Teflon (secondary) seal were damaged.

The AAIU summarized the sequence of events:

The Boeing 767 aircraft departed from Dulles International Airport (KIAD) in the United States at approximately 22:21 hrs on 6 April 2022, on a scheduled passenger flight to Zurich Airport (LSZH) in Switzerland. At approximately 04:13 hrs, when the aircraft was at Flight Level 360 and located approximately 20 nautical miles off the south coast of Ireland, the Flight Crew contacted Shannon Air Traffic Control (ATC) to declare an ‘emergency’, stating that they wished to divert to Shannon Airport (EINN) as they needed to shut down an engine due to low oil pressure. ATC cleared the aircraft to EINN, where it landed at approximately 04:40 hrs with the No. 1 engine shut down.

When the aircraft was taxiing towards its parking stand, the Airport Fire and Rescue Service noticed a fire at the left-hand undercarriage and requested (via the Shannon Ground Movements Controller) the aircraft to stop. The aircraft stopped and while the fire was being extinguished, the Airport Fire and Rescue Service requested (via the Shannon Ground Movements Controller) that the aircraft be evacuated on the right-hand side. Moments later, the request was cancelled, as the fire had been extinguished. The aircraft was subsequently towed onto its parking stand and all passengers and crew disembarked the aircraft normally. No injuries were reported to the Investigation.

The low oil pressure on the No. 1 engine was subsequently found to have been due to an oil leak from the engine’s No. 4 bearing scavenge line magnetic chip detector, which had been inspected as part of scheduled maintenance conducted prior to the flight. The probable cause of the brief fire at the left-hand undercarriage was heat from the brake units and the presence of lubrication grease or oil that had leaked from the No. 1 engine.

Related Flight: UA52, Twitter: #UA52, United Airlines News