History of Flight
On July 11, 2014, at 13:28 Pacific daylight time, Delta Air Lines Flight 101, a Boeing B-767-332 (registration N139DL), departed Los Angeles International Airport (LAX) bound for Hartsfield-Jackson Atlanta International Airport. During climb at flight level 190 (approximately 19,000 feet), the flight crew observed a left engine (No. 1) fire indication. They declared an emergency, performed the Quick Reference Handbook engine fire procedures (shutting down the affected engine), and initiated a return to LAX. After engine shutdown, the fire warning extinguished; no fire suppression bottles were discharged. The airplane made a successful overweight single-engine landing at LAX. Aircraft Rescue and Fire Fighting personnel met the aircraft and observed no damage. The airplane taxied to the gate without incident. No injuries were reported among the 200 passengers, 8 crew members, and 1 cockpit jump-seater on board. The flight was conducted under 14 Code of Federal Regulations Part 121 as a domestic passenger flight. Day visual meteorological conditions prevailed, and an instrument flight rules flight plan was filed.
Engine Examination
On July 21–24, 2014, a Powerplant Group (including representatives from General Electric, Boeing, Delta, ALPA, FAA, and NTSB) examined the incident engine at Delta's Technical Operations facility. Fire damage was concentrated under the engine heatshield from about the 6:00 to 8:30 o'clock position (aft looking forward) and forward of the accessory gearbox. The damage included melted and consumed electric wire insulation, consumed accessory gearbox fire loop isolators, melted and consumed tubing P-clamps, exposed conductors, and soot deposits.
Leak testing during wet motoring revealed a fuel leak from the integrated drive generator (IDG) fuel/oil heat exchanger main housing at about the 12:00 o'clock position, aft of the forward weld (fuel inlet port). The unit was removed; additional leak tests and fluorescent penetrant inspection confirmed a circumferential through-wall crack in-line with the braze joint of the inner core into the main housing, plus a second crack indication adjacent to the through-wall crack. No internal leak was found between the fuel and oil sides of the inner core.
Examination of IDG power feeder cables showed evidence of chafing and arc burn; however, this damage was not related to the actual fire damage. The cables (below the engine heatshield) were not tight and straight along their support bracket but exhibited slack and dangling. A review of installation drawings and exemplar aircraft found that the cables should run straight and tight along the bracket. Delta's work cards included sketches showing proper routing with no slack. The cables also had excessive orange tape bundling them together. The slack allowed the cables to become pinched between the inside of the thrust reverse cowl and the accessory drive lube and scavenge pump pressure line support bracket when the cowl was closed, causing chafing. The excessive tape suggested maintenance personnel may have noticed chafing and added tape without realizing the root cause.
Metallurgical Examination
Metallurgical examination of the IDG fuel/oil heat exchanger at the NTSB Materials Laboratory found that the fracture surfaces of the through-wall crack showed features consistent with multiple fatigue crack initiation sites emanating from the inner diameter surface of the main housing, propagating radially outward. A second fatigue crack location (not through-wall) exhibited cracks from both inner and outer diameters but did not link up. No anomalies were detected at the crack origins or in the base material, which was consistent with manufacturer specifications.
Corrective Actions
Following the incident, Delta updated its IDG power feeder work cards to provide additional guidance on proper routing both above and below the engine heatshield. A one-time fleet inspection for misrouted IDG power feeder cables found three additional engines with misrouted cables, bringing the total (including both engines on the event aircraft) to five. Delta promptly corrected all non-conforming routing.