An aircraft engine fan blade that broke during a United Airlines flight last month had thousands of flights before it underwent a federal government-mandated inspection, the National Transportation Safety Board said Friday.
The Pratt & Whitney engine with that blade caught fire and threw debris over homes minutes after the plane left Denver for Honolulu on February 20. The pilots flipped the plane and returned to the Denver airport. The outage, similar to an incident in Japan in December and one on another United aircraft in 2018, forced regulators and airlines around the world to ground more than 120 Boeing 777 aircraft powered by that particular family of engines, the PW4000- 112, were driven.
The Federal Aviation Administration ordered an immediate inspection of the fan blades in these engines. United, which has more than 50 such aircraft, was the only American airline affected by this order. The tests, known as “thermoacoustic inspections,” are performed by Pratt & Whitney and include bombarding the blades with pressure to heat them and looking for temperature anomalies that could indicate internal cracks.
Early evidence suggests one of the engine’s fan blades broke in flight last month and hit and broke another, according to the NTSB, which is investigating the failures. This first blade had flown approximately 3,000 flights since Pratt & Whitney last subjected it to a thermal acoustic inspection, well below the 6,500-flight threshold that the blades are regularly inspected using this technique.
This blade was last inspected in 2016, and the records of that inspection were reviewed in 2018 following the failure of another Pratt & Whitney engine on a United-operated Boeing 777. Following that near Hawaii incident, Pratt & Whitney updated its inspection recommendations, saying the blades should be tested more frequently, with the recommendation being introduced for 6,500 flights. The FAA later made this interval mandatory. A Japan Airlines Boeing 777 powered by a Pratt & Whitney engine suffered a similar engine failure in Japan in December.
After the United flight failed last month, Pratt & Whitney said it would recommend inspections every 1,000 flights, according to the NTSB