A fatigue crack in a turbine disk web and subsequent uncontained engine failure led to the Sept. 8, 2015 engine fire on a British Airways (BA) Boeing 777-236ER on takeoff from Las Vegas, the US National Transportation Safety Board (NTSB) said June 20.

The captain aborted the takeoff seconds after hearing a “bang” during the takeoff roll at Las Vegas McCarran International Airport. The flight’s destination was London Gatwick Airport; 157 passengers and 13 crewmembers on board evacuated via emergency slides.

NTSB said it found a fatigue crack in the high-pressure compressor stage 8 disk web of the aircraft’s left GE Aviation GE90-85BG11 engine. The web in a turbine engine rotor disk extends radially from the disk hub to its rim. The engine failure led to the detachment of the main fuel supply line and subsequent fire.

The high-pressure compressor stage 8-10 spool in the left engine had accumulated 11,459 total cycles. NTSB’s investigation found that the disk web crack started after about 6,000 cycles, “much earlier than the engine’s manufacturer, GE, predicted; the cause of the crack initiation could not be identified,” NTSB said.

GE and FAA did not require inspections of the disk web, so the crack went undetected. During maintenance in September 2008, when the high-pressure compressor was removed from the engine and disassembled, exposing the stage 8-10 spool, the surface crack length would have been about 0.05 inches.

“If the disk web had been required to be inspected during this maintenance, the crack should have been detectable,” NTSB said. After the accident, GE implemented inspection procedures designed to detect disk web cracks.

NTSB also faulted the 777’s captain for not using his quick reference handbook to immediately shut down the right engine, noting that the unaffected engine continued to run for 43 seconds after the captain’s order to evacuate, “resulting in jet blast blowing two emergency slides out of position and rendering them unusable for the evacuation.”

In a statement, a BA spokesperson said: “We fully supported the NTSB investigation, which did not identify any safety recommendations for British Airways. The safety of our customers and crew is always our very first priority. Our crew responded quickly and decisively bringing the aircraft to a swift halt, assessing the situation and safely evacuating the aircraft.”

Bill Carey, bill.carey@aviationweek.com