What happened
On 20 July 2021, a Boeing 747-8F, registration N624UP, operated by United Parcel Service Company, departed from Hong Kong International Airport bound for Dubai. Approximately four minutes after takeoff, the flight crew observed excessive engine speed on the left outboard (No. 1) engine. In response, the crew shut down the engine and initiated an emergency return to the airport.
Upon landing on Runway 07L, the No. 1 engine caught fire while the airport fire contingent was applying water to the aircraft. There were no injuries to the three crew members on board, though the engine sustained thermal damage.
The investigation
The AAIA investigation, supported by the NTSB, Boeing, GE, and Woodward, involved a detailed examination of the engine at a GE facility in Kentucky. Investigators performed fuel leak checks and pressure cycle testing on the fuel metering unit (FMU).
Technical analysis focused on the supply pressure (P1) bypass valve port fitting. Testing revealed that the fitting was not properly seated, leaving a gap between the fitting and the housing. Furthermore, the inspection showed that the packing for the fitting had been damaged.
Findings
- The primary cause of the incident was the improper installation of the P1 bypass valve port fitting on the fuel metering unit.
- This installation error created a fuel leak from the supply pressure bypass valve port fitting.
- The leak was sufficient to ignite and cause the engine fire.
- The fitting was found to be "finger loose," and the associated packing was damaged.