Pilot Debrief

BOEING 757-232 near Atlanta, GA — 2011-06-21

Final reportENG11IA035
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Date
2011-06-21
Location
Atlanta, GA, USA
Aircraft
BOEING 757-232
Registration
N6714Q
Category
Airplane
Highest injury
Minor
Fatalities
0

Probable cause

Fuel leaking from the fuel flow transmitter that ignited on contact with the engine’s hot cases which resulted in an engine undercowl fire. The fuel leak resulted from the fuel flow transmitter end housing backing off from the main housing, creating a gap that allowed high pressure fuel to escape. Under certain assembly variances and operational load and temperature variations, the end housing joint may not be able to maintain the preload without eventually yielding, which results in the loosening of the joint and the resultant gap.

NTSB narrative

On June 21, 2011, about 0007 eastern daylight time, a Boeing B-757-232, N6714Q, powered by two Pratt & Whitney (P&W) PW2037 turbofan engines, experienced a left engine (No. 1) fire while taking off from Atlanta’s Hartsfield International Airport (ATL), Atlanta, Georgia. The Captain declared an emergency, shutdown the No. 1 engine, and a turnback to ATL was initiated. The airplane made a successful overweight, single-engine landing, and an emergency evacuation was conducted on the right side of the airplane onto the runway. Of the 172 passengers and 6 crewmembers on board the flight, 3 passengers received minor injuries associated with the slide evacuation. The airplane was operated by Delta Airlines as a 14 Code of Federal Regulations Part 121 domestic passenger flight from ATL to Los Angeles International Airport, Los Angeles, California. Night visual meteorological conditions prevailed at the time, and an instrument flight rules flight plan was filed. Examination of the engine found extensive fire damage and thermal distress in the fan and core compartments with the vast majority of the thermal distress and the most extensive fire damage located in the fan compartment between and including the intermediate case and the turbine exhaust case. The end housing of the fuel flow transmitter (FFT) was found backed-off from the main housing, which created a gap of about 0.3 inch at the bottom of the unit; correspondingly the FFT-to-fuel distribution valve (FFT-to-FDV) fuel line was found plastically deformed. An installation fit check coupled a deflection analysis of the FFT-to-FDV fuel line revealed that the deformation of the fuel tube was as a result of the FFT end housing separation; it did not cause the gap. Metallurgical analysis of the FFT hardware did not find any material defects or anomalies. Torque tension tests and a finite element analysis of the loads applied to the FFT revealed that under certain assembly variances and operational load and temperature variations, the load capability of the end housing-to-main housing bolted joint was marginal or less than marginal. With reduced load capability, the main housing threads would not be able to maintain the preload without eventually yielding, which would result in lessening of the preload and loosening of the joint. A review of the FFT component maintenance manual (CMM) found several areas where improvements could be made to ensure a more consistent FFT assembly practice and proposed changes have been initiated to the CMM.

NTSB coding

  • Powerplant sys/comp malf/fail · Takeoff
View NTSB final report

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