Boeing 767 332 N139DL incident near Los Angeles, California

Probable cause

The combination of fuel leaking from the integrated drive generator (IDG) fuel/oil heat exchanger and the coincident arcing of the IDG power feeder cables that ignited the leaking fuel. Contributing to the ignition of the fuel was the misrouting of the IDG power feeder cables, which resulted in chaffed cables that exposed the electrical wire that contacted a metal bracket, creating an arc.

NTSB analysis

On July 11, 2014, a Boeing B-767-332, registration number N139DL, operated by Delta Air Lines (DAL), and powered by two General Electric (GE) CF6-80A2 turbofan engines, experienced a left engine (No. 1) fire during climb from Los Angeles International Airport (LAX), Los Angles, California. The flightcrew reported observing a left engine fire indication during climb and declared an emergency, performed the Quick Reference Handbook (QRH) engine fire procedures which included shutting down the affected engine, and an air turnback to LAX was initiated. The airplane made a successful and uneventful overweight single-engine landing at LAX and Aircraft Rescue and Fire Fighting (ARFF) personnel met the aircraft and observed no damage. The airplane taxied to the gate without incident. Delta maintenance personnel opened the left engine cowling and observed heat damage, scorching, and sooting.

An examination of the engine revealed that the fire damage was concentrated underneath the engine heatshield on the left side of the engine. Flow testing of the engine revealed a fuel leak from the integrated drive generator (IDG) fuel/oil heat exchanger main housing. This was determined to be the source of the flammable fluid leak. Metallurgical examination of the IDG fuel/oil heat exchanger found a through-wall fatigue crack but no anomalies were found at the crack initiation site. The portions of the IDG power feeder cables located underneath the engine heat shield and in the general vicinity of the IDG fuel/oil heat exchanger revealed evidence of chaffing and arc burns and exhibited a considerable amount of orange tape to bundle all the cables together. The accessory drive lube and scavenge pump pressure (supply) line support bracket exhibited evidence of melted material consistent with an arc burn. The locations of the arc burn on the support bracket and the power feeder cables were in-line with one another and were the source of the electrical spark that ignited the fuel. Review of the IDG power feeder cable installation below the engine heatshield on the event engine revealed that they were misrouted creating excessive slack and dangling below the support bracket. This excessive slack in the IDG power feeder cables created the situation where the cables could get pinched/wedged between the inside of the thrust reverse cowl and the accessory drive lube and scavenge pump pressure (supply) line support bracket when the thrust cowl is closed and latched, creating the environment for the IDG power feeder cables to chaff against the support bracket. The excessive amount of tape used on the IDG power feeder cables suggests that maintenance personnel may have noticed this chaffing and added extra tape without realizing that the chaffing was caused from the thrust reverser pressing the IDG power feeder cables against the bracket or that the slack was contributing to the chaffing. DAL inspected their entire fleet of CF6-80A2 powered Boeing 767 and corrected any IDG power feeder cables that had been misrouted.

Text from the NTSB. Open the NTSB docket for ENG14IA019 for the full record.