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The National Transportation Safety Board revealed that the right engine failed within minutes of takeoff from Denver airport, when the plane’s pilots strangled the engines “to minimize the weather in the expected turbulence.”
“Immediately after advancing the throttles, a popping sound was recorded” on the cockpit voice recorder.
The new details are part of an update from the NTSB in its ongoing investigation, which typically takes a year or more. The seven pages The report did not draw any conclusions as to the cause of the incident, nor did it direct any further action to be taken by the Federal Aviation Administration, aircraft operators, or the engine manufacturer.
A warning light indicated a fire in the engine, according to the update. The pilots followed a procedure to fight the fire and determined that they would not spill fuel to make the aircraft lighter before landing. They concluded that “the magnitude of the overweight landing was not large enough to outweigh other considerations,” the NTSB said.
The report said that a valve that shut off the flow of fuel to the engine in the event of a fire had properly closed and said “there was no evidence of a fuel-fed fire.” The report cited damage to “fuel, oil and hydraulic lines”.
The NTSB report says the failed fan blade was inspected using specialized thermal acoustic imaging technology in 2014 and 2016. The inspection looks for tiny cracks or signs of metal fatigue that can not be visible to the naked eye.
After an engine incident in 2018 on another aircraft, the 2016 data was again analyzed, the NTSB said.
The report noted that when the fan blade failed last month, it was less than halfway to requiring another inspection – a detail CNN has previously reported. It had run 2,979 cycles, a rough measure of the number of times the engine was started and stopped. Inspection was required after 6,500 cycles.
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 requiring engine fan blades 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 panel met days before the February engine failure to consider requiring more regular inspections.
Following the engine failure, Boeing recommended suspending use of the 777s equipped with the Pratt & Whitney 4000 engine, and United Airlines has already withdrawn its 777s following the incident. FAA and NTSB are investigating.
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