Failure to follow maintenance procedures has been cited as a contributory factor in a ‘serious incident’ which resulted in a transatlantic flight making an emergency landing at Shannon Airport almost two years ago.
The Air Accident Investigation Unit (AAIU) of the Department of Transport has issued its final report into an incident which occurred on April 7th 2022 when the crew of a United Airlines flight had to shut down one of the aircraft’s two engines in flight.
Flight UA-52 was travelling from Washington in the United States to Zurich, Switzerland at the time with 117 passengers and 9 crew on board.
At approximately 4:13 on the morning of the incident, while flying at 36,000 feet about 20 nautical miles (37 kilometres) off the south coast of Ireland, the flight crew contacted air traffic controllers to declare an ‘emergency’, stating they wished to divert to Shannon Airport as they needed to shut down an engine due to low oil pressure.
As the flight routed towards Shannon, emergency procedures were implemented at the airport. Units of Clare County Fire and Rescue Service from Shannon and Ennis stations were mobilised to the airport in support of Shannon Airport’s own fire and rescue crews. National Ambulance Service paramedics and Gardaí were also dispatched to the airport as part of the emergency plan.
According to the AAIU report, Shannon ATC cleared the aircraft to Shannon, where it landed at approximately 4:40am with the No. 1 engine shut down.
When the Boeing 767-300(ER) jet was taxiing towards its parking stand, Airport Fire and Rescue Service crews noticed a fire at the left-hand undercarriage and requested, via the Shannon ground movements controller, the aircraft to stop.
The plane came to a stop and while the fire was being extinguished, the Airport Fire and Rescue Service requested 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.
Low oil pressure in the No. 1 engine was subsequently found to have caused by an oil leak from the engine’s No. 4 bearing scavenge line Magnetic Chip Detector (MCD), which had been inspected as part of scheduled maintenance conducted prior to the flight.
The probable cause of the brief fire in the left-hand undercarriage was heat from the brake units combined with the presence of lubrication grease or oil that had leaked from the No. 1 engine.
The AAIU has said that the probable cause of the incident was: “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.
Among the contributory causes cited were that “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.”
As a result of the actions taken by the aircraft Operator, the Engine Manufacturer, and the Aircraft Manufacturer following the occurrence, the AAIU Investigation does not sustain any Safety Recommendations.
