On July 7, 2016, a BOEING 757 2Q8 (registration N706TW) operated by DELTA AIR LINES INC was involved in an aviation accident near Jamaica, NY. No fatalities were reported. Investigators recorded the probable cause as: Maintenance personnel's failure to ensure proper installation of a fuel tube O-ring, which resulted in an undercowl engine fire during initial climb. This summary draws on records from NTSB; 17 related events involving the same aircraft type or operator are linked below.
On July 7, 2016, a Delta Air Lines Boeing 752, N706TW, experienced a right engine fire shortly after takeoff from JFK. The crew shut down the engine, and the aircraft returned to JFK and landed safely with minor damage.
Incident Overview and Immediate Response On July 7, 2016, at approximately 1307 UTC, a Delta Air Lines Boeing 752, registration N706TW (MSN 6804), encountered a right engine under-cowl fire shortly after departing John F. Kennedy International Airport (JFK) in Jamaica, NY. The flight was operating as a 14 CFR Part 121 scheduled service to San Diego International Airport (SAN). The crew received a right engine fire warning at roughly 400 feet above ground level and declared an emergency. The right engine was shut down, after which the fire warning extinguished. No fire bottles were discharged. The aircraft returned to JFK and landed without incident. Airport rescue and firefighting units did not detect an active fire upon arrival. No injuries were reported, and the aircraft sustained minor damage. ## Aircraft Damage and Fire Examination Post-incident inspection revealed that thermal damage was confined to the right nacelle. The aft 11 inches of the thrust reverser cowl inner fan duct flowpath showed blistered paint. The ablative coating on the inner thrust reverser cowl surfaces remained intact between 12 and 3 o'clock but was charred and fractured between 3 and 12 o'clock, exposing some underlying honeycomb structure. The skin at the aft end of the outboard core cowl was buckled between 4 and 6 o'clock. A 25-inch long axial hole was present in the inboard core cowl, measuring 3.5 inches wide at the forward end and 14.5 inches wide at the aft end, and included the aft edge of the pressure relief door cut-out. Rough, matte-gray deposits adhered to the aft end of the exhaust nozzle outer surface between 4 and 10 o'clock. Engine thermal distress was limited to the core compartment fire zone, with soot deposited over the entire engine and general thermal distress to external components, most pronounced between 4 and 12 o'clock. ## Maintenance History and Engine Examination The engine had accumulated 51,142 flight hours and 18,855 cycles since new, and 3,871 hours and 965 cycles since its last shop visit. Records indicated recent maintenance to address an anomalous fuel flow signal. A fuel flow transmitter (FFT) replacement on July 6, 2016, did not resolve the issue, and further maintenance was deferred per the minimum equipment list. A second FFT was installed on July 7, 2016. A 10- to 15-minute post-maintenance engine check run showed normal fuel flow indications and no leaks, and the aircraft was released to service. The fire occurred during the next flight. Engine examination found no evidence of mechanical failure or uncontainment. Most electrical harnesses, tube/harness insulation, and attachment hardware inside the core compartment exhibited thermal distress, including melted or missing fire loop grommets, melted harness insulation, eroded P-clamp cushions, and whitened, flaking flexible fuel line fire sleeves. The turbine case cooling line was ruptured 21.5 inches aft of the V-groove at 9 o'clock, with a two-inch-wide rupture and petalled outward fractured edges. The fan air valve actuator housing was heat-deformed and partially consumed. The most severe fire damage occurred at the diffuser/high-pressure turbine (HPT) between 6 and 9 o'clock, where bare wires were observed and engine burner temperature, turbine cooling air, and EGT signal wires and aft lower fire loops were separated. The darkest sooting appeared between 6 and 7 o'clock, where the FFT assembly shell was partially consumed by fire. A rubbery blue-colored substance was noted protruding from the top and left sides of the FFT-to-fuel OUT tube joint. Delta Tech Ops determined that the flammable fluid source was fuel leaking at the FFT-to-fuel OUT tube joint. ## FFT Assembly and O-Ring Evaluation The FFT, fuel IN line, and fuel OUT line were removed as an assembly. Pressure testing revealed leakage at the suspect joint. Upon removal of the fuel OUT tube, the tube O-ring was found eroded with a 90° arc of material missing. Both ends of the O-ring separation exhibited shallowly angled separations. A new P/N M25988/3-217 O-ring was lubricated and installed in the tube gland for re-testing. The B757 AMM FFT installation procedure, Task 73-31-01-404-018-P00, did not instruct lubrication of the O-ring prior to installation and erroneously indicated that the O-ring should be installed onto the FFT rather than on the fuel tube. The tube was reassembled to the FFT, and retaining bolts were torqued to the minimum required torque per the engine manual (65 lb. in). The AMM task did not provide bolt attachment torque values. The original O-ring was retained and submitted to the NTSB Materials Lab. Fourier Transform Infrared spectrometry confirmed that the O-ring material conformed to the drawing specification. Parker Aerospace assessed the O-ring separation, reporting that similar angle/plane cuts on both ends are a commonly observed damage condition resulting from installation error. ## Maintenance Instruction Review Review of the B757 AMM FFT installation procedure identified three issues: a) the task did not include an instruction to lubricate the tube O-rings prior to installation; b) it incorrectly directed that the fuel IN and fuel OUT tube O-rings be installed on the FFT rather than into the fuel tube O-ring glands; and c) it did not specify a torque value for the tube attachment bolts. The FFT installation task used by the Delta technician directly aligned with the Boeing AMM and therefore included these omissions and errors. Parker Hannifin Publication ORD5700, Parker O-Ring Handbook, page 3-4, paragraph 3.1.5, states that using a suitable grease or oil during assembly helps protect the O-ring from damage by abrasion, pinching, or cutting and helps the O-ring to seat properly.
