The National Transportation Safety Board revealed that the right engine failed a few minutes after takeoff from the airport in Denver when the pilots of the plane accelerated the engines “to reduce time in expected turbulence.”
“Immediately after the gas forces advanced, a loud bang was recorded” on the cabin’s voice recorder, CNN reported.
The new details are part of an update from the NTSB in the ongoing investigation, which usually takes a year or longer to complete. The seven-page report did not draw 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.
According to the update, a warning light indicated a fire in the engine. The pilots followed a procedure to fight the fire and determined that they would not pour fuel to lighten the plane before landing. They concluded that ‘the extent of the overweight landing was not significant enough to weigh other considerations,’ the NTSB said.
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The report says that a valve that cuts fuel flow to the engine in case of fire closed properly and it is said that there was no evidence of a fuel being fed. The report cites damage to the “fuel, oil and hydraulic pipelines.”
The plane returned safely to Denver International Airport without injuries on board or on the ground, where debris rained from the plane in a residential area in Broomfield, Colorado. The report states that the engine caught fire after landing, but that the firefighters ‘quickly extinguished’.
The NTSB report states that the fan blade that failed was inspected in 2014 and 2016 using specialized thermal acoustic imaging technology. The inspection is looking for small cracks or signs of metal fatigue that may not be visible to the naked eye.
After an engine incident in 2018 on another level, 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 need a new inspection – a detail CNN reported earlier. 2,979 cycles were used, an approximate measure of how many times the engine was turned on and off. Inspection was required after 6500 cycles.
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The day after the incident in February, engine manufacturer Pratt & Whitney recommended that the inspection interval be dramatically reduced to just 1,000 cycles, according to a service bulletin obtained by CNN. The FAA has issued an emergency guideline requiring the fan blades to be inspected on the engines before being flown again.
The inspection interval for this engine range was of concern to federal regulators. CNN previously reported that a Federal Aviation Administration review board met just days before the February engine failure to consider requiring more frequent inspections.
In the wake of the engine outage, Boeing recommended suspending the use of 777s with the Pratt & Whitney 4000 engine, and United Airlines had already pulled its 777s after the incident. Both the FAA and the NTSB are investigating.
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