What happened
On 20 November 2018, a Boeing 747-443, registration G-VROY, was preparing for a commercial passenger flight from London Gatwick to Orlando. The aircraft had recently completed heavy maintenance at an overseas facility. During the engine start sequence at Stand 566, the ground engineer observed flames emerging from the No 2 engine tailpipe.
In response, the flight crew immediately moved the fuel control switch to the cut-off position and executed the relevant fire drill from the quick-reference handbook. While the fire was extinguished, the airfield fire services attended the scene. The remaining engines were shut down, and the aircraft was towed back to the stand, where all 398 passengers and 18 crew members were safely disembarked. There were no injuries reported.
The investigation
The investigation focused on identifying the cause of the sudden flame in the tailpipe. Physical inspections of the aircraft revealed heat damage to the inboard flaps, several access panels, and the flap track fairing.
Analysis of the quick-access recorder (QAR) data revealed a significant anomaly: prior to the rotation of the No 2 engine compressor, the fuel metering valve showed a fuel demand of 119%, whereas the other engines required only 11%. To investigate this, the hydro-mechanical unit (HMU) and various other valves and controllers were sent to the manufacturers for testing. These components were found to be operating within normal parameters. Additionally, a review of the recent heavy maintenance work found no errors in the procedures or the application of fuel tank biocidal treatments.
Findings
- The investigation established that a massive surge in fuel flow through the fuel metering valve into the combustion chamber occurred during the start sequence.
- This excessive fuel flow was the primary cause of the engine tailpipe fire.
- It is suspected that residual debris from a recent biocidal treatment applied to the fuel tanks may have interfered with the operation of the HMU valves, although no specific fault could be identified in the hardware.