What happened
On July 07, 2016, a Boeing 757, registration N706TW, operated by Delta Air Lines, experienced a right engine under-cowl fire shortly after takeoff from John F. Kennedy International Airport (JFK) in Jamaica, NY. The aircraft was performing a scheduled flight to San Diego International Airport.
At approximately 400 feet above ground level, the flight crew received a right engine fire warning and declared an emergency. The crew responded by shutting down the right engine, which caused the fire warning to extinguish. No fire extinguisher bottles were discharged during the event. The aircraft returned to JFK and landed without further incident. There were no injuries and the aircraft sustained minor damage.
The investigation
Flight data recorder analysis showed the fire warning occurred approximately three seconds before lift-off and remained active for about 45 seconds. Engine parameter data began to drop approximately 55 seconds after the warning, with all engine signal data lost about 24 seconds later, which was consistent with wire damage found during the examination.
Post-incident inspections of the engine revealed that thermal damage was concentrated in the right nacelle. The inspection found a 25-inch long hole in the inboard core cowl caused by burn-through. While soot was present over the entire engine, the most severe damage was located in the core compartment fire zone, where the fuel flow transmitter (FFT) assembly shell was partially consumed.
Maintenance records indicated that on the morning of the flight, the right engine fuel flow transmitter had been replaced. An investigation into the FFT assembly revealed that the O-ring at the FFT-to-fuel OUT tube joint had been eroded, with a 90-degree arc of material missing. Evaluation by Parker Aerospace determined that the specific type of cuts found on the O-ring are a common result of installation error.
Findings
- The source of the flammable fluid was fuel leaking from the FFT-to-fuel OUT tube joint.
- The O-ring in the joint had been severed during maintenance, which compromised its ability to seal.
- During takeoff, high-pressure fuel escaped through the damaged seal and sprayed into the engine core compartment, where it ignited upon contact with hot surfaces.
- The Boeing 757 Aircraft Maintenance Manual (AMM) task used for the installation contained several errors: it did not instruct technicians to lubricate the O-rings before installation, it incorrectly directed that the O-rings be installed on the FFT rather than the fuel tube, and it failed to provide a torque value for the attachment bolts.
- The technician's installation followed the erroneous instructions provided in the AMM.