U.S. aviation regulators on Tuesday issued stringent new inspection requirements to ensure Pratt & Whitney engines like the one that broke apart over a Denver suburb on Saturday are safe.
The Federal Aviation Administration’s airworthiness directive mandates that the titanium fan blades on certain Pratt & Whitney engines be examined with a special test to essentially peer inside the surface before they can return to service.
The action was prompted by the violent failure of a fan blade on one of two engines mounted on a United Airlines plane, a Boeing Co. 777-200. After the 40.5-inch (103-centimeter) blade snapped, it tore off another blade and the front structure of the engine, pelting a suburban neighborhood with metal and other debris.
No one was hurt on the ground and the plane landed safely.
“As these required inspections proceed, the FAA will review the results on a rolling basis,” the agency said in an emailed statement. “Based on the initial results as we receive them, as well as other data gained from the ongoing investigation, the FAA may revise this directive to set a new interval for this inspection or subsequent ones.”
All 777s using this engine, only about 69 of which were in service around the world, were effectively grounded while awaiting the FAA’s action. Japan ordered its carriers to halt flights while United voluntarily stopped using the planes. Another 59 are in storage, according to Boeing.
South Korea issued its own inspection order earlier Tuesday.
The U.S. order applies to Pratt & Whitney PW4000 engines with 112-inch diameter fan blades. There are several versions of the engine, all of them on 777s. Most 777s use engines built by other manufacturers and those are unaffected.
Pratt & Whitney is a division of Raytheon Technologies Corp.
Most of the destruction in Saturday’s failure was confined to the engine, but some material hit the plane, causing minor damage, National Transportation Safety Board Chairman Robert Sumwalt said on Monday. The pilots made an emergency landing and no one was hurt.
The preliminary evidence is that the blade suffered from metal fatigue, Sumwalt said. When metal fatigues, a crack can grow progressively longer each time it is stressed as the engine starts up. Such cracks can linger for years before they lead to failure.
In March 2019, the FAA issued a directive on the same engines following a similar failure on a United jet flying from San Francisco to Hawaii on Feb. 13, 2018.
It required that the fan blades be inspected before reaching a total of 7,000 flights. Once those were completed, operators had to repeat the inspections within the next 1,000 flights, according to the earlier directive.
As in the most recent order, it called for use of a technique called thermal acoustic imaging that is similar to an ultrasound for use in medicine. By bombarding the titanium blades with energy waves, defects within the metal can be detected.
Pratt & Whitney conducted 9,600 inspections on blades after that 2018 failure, the NTSB said after completing an investigation into the failure.
Investigators concluded Pratt & Whitney employees had missed a growing crack in the blade during inspections in 2010 and 2015, partly as a result of inadequate training. In 2015, an inspector dismissed the evidence of a crack as a distortion caused by paint, the NTSB said.
The FAA is planning on sharing its order with other nations, which often follow the U.S. agency’s lead.
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