The Federal Aviation Administration (FAA) on Friday issued an emergency airworthiness directive for 2,000 US-registered Boeing 737 NG and Classic aircraft, warning of possible corrosion on parked planes that could lead to a dual-engine failure.
Inspectors found compromised air check valves when bringing aircraft out of storage following four recent reports of single-engine shutdowns on planes that had been parked, prompting the directive for aircraft not operated for seven or more straight days.
Alaska Airlines said one of its aircraft is likely one of the four incidents, noting a recent engine shutdown issue.
“The safety of the flight was not compromised,” Alaska said in a statement, adding it is now inspecting the check valves before returning planes to service.
If airlines find corrosion, they must replace the valve prior to flying the aircraft again, the FAA said.
Boeing Co said on Friday that it had advised operators to inspect the planes and added, “with airplanes being stored or used infrequently due to lower demand during the COVID-19 pandemic, the valve can be more susceptible to corrosion.”
Global airlines parked thousands of aeroplanes after the coronavirus pandemic sharply reduced travel demand, but some have started flying again as demand picked up.
The FAA said the directive is to address corrosion of the engine bleed air 5th stage check valves for both engines. The agency said that could result in compressor stalls and dual-engine power loss without the ability to restart.
Boeing said it is providing inspection and replacement information to fleet owners if they find an issue.
Among other US operators of the 737, American Airlines and Southwest Airlines said they are complying with the directive but had not experienced any issues.
United Airlines and Delta Air Lines also said they are complying and do not anticipate any impact on operations.