U.S. aviation regulators have 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.
Before the jets can fly again, the large, hollow fan blades at the front of each engine must be removed and shipped to a Pratt & Whitney facility where they will undergo a "thermal acoustic image" inspection, according to the FAA. Under that technique, a fan blade is bombarded with high-frequency vibrations, raising its temperature. A thermal image of the blade is then recorded and analyzed for unusual readings that may signify a potential crack.
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 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.
In 2018, a United Airlines flight involving the same plane-and-engine combination suffered a similar failure on a flight from San Francisco to Hawaii, prompting the FAA to order engine inspections every 6,500 flights. In its statement Tuesday, the agency said it might still adjust that inspection frequency.
Pratt & Whitney conducted 9,600 inspections on blades after that 2018 failure, the National Transportation Safety Board 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 board said.
"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 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.
Information for this article was contributed by Niraj Chokshi of The New York Times.