History of Flight
On September 6, 2017, at about 0019 Pacific Daylight Time, a Delta Air Lines Boeing 757-232, registration N686DA, equipped with two Pratt & Whitney PW2037 turbofan engines, was taking off from McCarran International Airport (LAS), Las Vegas, Nevada. During rotation and initial climb, the flight crew received a left engine fire indication with an associated aural fire alert. The crew performed the quick reference handbook (QRH) procedures, declared an emergency, shut down the No. 1 (left) engine, and discharged one fire bottle. The fire warning momentarily cleared.
The crew initiated engine-out procedures to return to LAS. While on the downwind leg, the fire warning re-illuminated, and the second fire bottle was discharged, which cleared the warning again. The airplane made an overweight landing at LAS and was met by aircraft rescue and firefighting (ARFF) personnel, who sprayed fire retardant into the engine and confirmed the fire was extinguished. The airplane was cleared to taxi to the gate under its own power. No passengers or crew injuries were reported. The flight was operated under 14 Code of Federal Regulations Part 121 as a regularly scheduled flight from LAS to John F. Kennedy International Airport (JFK), Queens, New York.
Damage to the Airplane
There was no damage to the airplane structure. The left engine thrust reverser exhibited thermal damage and discoloration on all interior surfaces except a localized area between the 1 and 3 o'clock positions where the insulation appeared wet and shiny. The core cowls were thermally damaged, deformed, and missing material.
Test and Research
The No. 1 engine was removed from the airplane by Delta Air Lines maintenance personnel and shipped to Delta TechOps in Atlanta, Georgia, for examination and disassembly. Representatives from Delta, Pratt & Whitney, Boeing, the Air Line Pilots Association, the Federal Aviation Administration, and the National Transportation Safety Board participated in the examination from September 26–28, 2017.
Compressor fan blades were all present and complete. Three fan blades at the 6 o'clock position exhibited midspan shroud shingling, with tips dug into the fan case rub strip and displaced about one inch aft. The fan could not be rotated by hand until the three shingled blades were forced back into position. After adjustment, the fan spun smoothly with concurrent rotation of the low pressure turbine.
All exterior engine surfaces aft of the fan exit case were sooted. The engine had thermal damage and dark discoloration most concentrated over the high pressure compressor (HPC) and diffuser cases on the lower half (3 to 9 o'clock positions). Fuel components including the stator vane actuator (SVA), fuel flow transmitter (FFT), and associated fuel lines were thermally damaged with melted and missing material, resulting in fuel system leak points. An SVA hose and tube assembly was found separated and hanging freely from the engine.
A leak check of the fuel manifolds and fuel nozzle assemblies was performed by porting shop air into the fuel flow divider valve. When pressurized air was applied, a leak was detected at fuel nozzle #7, located at the 3 o'clock position. The nozzle was removed as an assembly by cutting the fuel manifold supply line. Preliminary X-rays indicated the fuel nozzle b-nut was not properly installed. The separated SVA hose and tube assembly was sent to the Pratt & Whitney Materials and Processes Engineering Lab for analysis.
X-rays at the Pratt & Whitney Quality and Standard Laboratory confirmed the b-nut was tilted relative to the nozzle platform and not centered with the nozzle fuel supply tube (cross-threaded). One or fewer threads were engaged between the nozzle and b-nut. The nozzle assembly was sectioned; the o-ring on the fuel nozzle side was intact, but the second o-ring on the fuel manifold supply line side was damaged, with fragments recovered outside the o-ring gland near the conical washer seal.
The SVA hose and tube assembly was examined. The flexible hose section exhibited thermal damage including a missing fire sleeve and hose liner. The hose liner was separated at one end of the connection to the rigid tube, but the other joint remained intact. Metallographic sections of both joints showed no significant differences.
Corrective Action
Following the event, Delta voluntarily inspected all PW2000 engines in the Delta TechOps repair shop, test cell, and spares pool for proper fuel nozzle installation, with no additional installation errors found. Shop records were reviewed, identifying two in-service engines overhauled or repaired around the same time as the incident engine; their fuel nozzles were inspected with no findings. To avoid future installation errors, the diffuser and combustor assembly work instruction card was updated to add an inspector sign-off requirement during the pneumatic leak check step of fuel system assembly.