The NTSB update also said a fan blade that failed in the Boeing 777’s engine had most recently received a close inspection for wear and tear in 2016 and was less than halfway to the point of requiring another inspection.
The NTSB investigation typically takes a year or more to complete. The seven-page report released Friday did not make any conclusions about the cause of the incident nor did it prescribe further steps for the Federal Aviation Administration, aircraft operators, or the engine manufacturer to make.
“Immediately after the throttles were advanced a loud bang was recorded” on the cockpit voice recorder, the report said.
Travis Loock, a passenger on Flight 328, said it was about 20 minutes after takeoff that he heard a boom.
The flight data recorder indicated “the engine made an uncommanded shutdown and the engine fire warning light activated shortly after,” the report said.
The pilots followed procedure to fight the fire, and determined they would not dump fuel to make the aircraft lighter before landing, the report said. They concluded that “the magnitude of the overweight landing was not significant enough to outweigh other considerations.”
The report said a valve that cuts fuel flow to the engine in case of fire had properly closed and said “there was no evidence of a fuel-fed fire.” The report cited damage to the “fuel, oil, and hydraulic lines.”
The report said the engine flared up in flames after landing at the airport but that “was quickly extinguished” by firefighters.
Part that failed last inspected in 2016
The NTSB report on Friday said the fan blade that failed was inspected using specialized thermal acoustic imaging technology in both 2014 and 2016. The inspection looks for tiny cracks or signs of metal fatigue which may not be visible to the naked eye.
After a 2018 engine incident on a different plane, the 2016 data was analyzed again, the NTSB said.
The report noted that when the fan blade failed last month, it was less than halfway to the point of requiring another inspection — a detail CNN has previously reported. It had been operated 2,979 cycles, an approximate measure of how many times the engine has been turned on and off. Inspection was required after 6,500 cycles.
Days after the February incident, engine manufacturer Pratt & Whitney recommended dramatically shrinking the interval for the inspection to just 1,000 cycles, according to a service bulletin obtained by CNN. The FAA issued an emergency directive requiring the fan blades on the engines to be inspected before flying again.
The inspection interval for this engine series has been a concern for federal regulators. CNN previously reported a FAA review board met just days before the February engine failure to consider requiring more regular inspections.
In the wake of the engine failure, Boeing has recommended suspending the use of 777s that have the Pratt & Whitney 4000 engine, and United Airlines has already pulled its 777s following the incident. Both the FAA and the NTSB are investigating.
CNN aviation analysts said at the time that such an engine failure was more likely to occur at takeoff, when the aircraft needs more power from the engines.
“If there’s a flaw hidden inside — between all those fans and turbines that are spinning around with such tremendous force and under such tremendous pressure and heat…