The National Transportation Safety Board revealed the correct engine failed minutes after takeoff from Denver airport when pilots of the plane accelerated the engines “to minimize the expected turbulence time.”
“Immediately after the throttle advance a loud bang was recorded” on the cabin’s voice recorder, CNN reported.
The new details are part of an NTSB update on its ongoing research, which typically takes a year or more to complete. The seven-page report made no conclusions about the cause of the incident nor did it prescribe additional measures for the Federal Aviation Administration, aircraft operators or the engine manufacturer.
According to the update, a warning light indicated a fire in the engine. The pilots followed a firefighting procedure and determined they would not spill fuel to make the plane lighter before landing. They concluded that “the magnitude of the overweight landing was not significant enough to offset other considerations,” the NTSB said.
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The report said a valve that cuts off fuel flow to the engine in the event of a fire had shut down properly and said “there was no evidence of a fuel-fired fire.” The report mentioned damage to “fuel, oil and hydraulic lines.”
The plane returned to Denver International Airport safely uninjured on board or ashore, where the wreckage of the plane rained down on a residential area of Broomfield, Colorado. The report said the engine caught fire after landing, but that firefighters “quickly extinguished.”
The NTSB report said the failed fan blade was inspected using specialized thermal acoustic imaging technology in both 2014 and 2016. The inspection looks for small cracks or signs of metal fatigue that may not be visible. at first glance.
After a 2018 engine incident on a different plane, the 2016 data was re-analyzed, 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, CNN has previously reported. 2,979 cycles had been operated, an approximate measure of how many times the engine has been started and turned off. Inspection was required after 6,500 cycles.
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Days after the February incident, engine maker Pratt & Whitney recommended drastically reducing the inspection interval to just 1,000 cycles, according to a service bulletin obtained by CNN. The FAA issued an emergency directive that required the blades of engine fans to be inspected before flying again.
The inspection interval for this series of engines has been a concern for federal regulators. CNN previously reported that a Federal Aviation Administration review board met a few days before the February engine failure to consider the need for more periodic inspections.
Following the engine failure, Boeing has recommended suspending the use of 777s that have the Pratt & Whitney 4000 engine, and United Airlines has already withdrawn its 777 after the incident. Both the FAA and the NTSB are investigating.
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