Incident Overview
On 20 November 2018, a Boeing 747-443, registration G-VROY, experienced a fire in the No 2 engine tailpipe during engine start while at London Gatwick Airport. The aircraft was being prepared for a commercial passenger flight to Orlando, Florida. There were 18 crew and 398 passengers on board; no injuries were sustained by any persons.
Sequence of Events
The aircraft had recently undergone heavy maintenance overseas and was operating its first revenue flight after that maintenance. During pushback from Stand 566 at North Terminal, engines were started. All flight deck indications were initially normal. However, partway through the start sequence for engine No 2, the ground crew engineer observed flames from the tailpipe and alerted the flight crew. The crew immediately selected the fuel control switch to cut off and completed the Quick Reference Handbook (QRH) procedure for an engine tailpipe fire. No temperature exceedances were reported. Airfield fire crews arrived shortly after the fire had been extinguished. The remaining engines were shut down, and the aircraft was towed back to the stand for passenger disembarkation.
Aircraft Examination and Findings
Post-incident examination revealed heat damage to the adjacent flap track fairing, several access panels, and the inboard flaps. Structural inspections found no significant damage, and cosmetic repairs and replacements were performed as needed.
Data from the Quick Access Recorder (QAR) showed that before engine No 2 compressor rotation, there was a large fuel demand through the fuel metering valve (FMV): 119% compared to 11% for the other engines. The Hydro-Mechanical Unit (HMU) was removed and sent to the manufacturer for analysis, but it was found to perform within expected limits. Several other valves and controllers were also examined by their manufacturers with no faults detected. All work from the preceding heavy maintenance was reviewed and no faults were found.
Discussion
Despite thorough strip, examination, and testing of various components, no fault could be identified to explain the increased fuel flow recorded. The high fuel flow into the combustion chamber during start would almost certainly cause an engine tailpipe fire. The ground crew quickly identified the fire and alerted the flight crew, who correctly actioned the checklist. A fuel tank biocidal treatment had been carried out during the heavy maintenance. Although the additive treatments were verified correct, the operator suspected that residual debris may have remained and could have affected the HMU valve operation.