We’ve covered here how much work goes into keeping stored aircraft in good condition, and for the most part those procedures do the job – even as an unprecedented number of planes have been parked worldwide. However the Boeing 737 has now had a maintenance issue crop up that is specifically related to storage. The FAA yesterday issued an Emergency Airworthiness Directive (AD) for Boeing 737s (-300 through -900ER series) after a series of recent engine shutdowns were shown to be caused by an engine bleed air valve being stuck open – apparently as a result of corrosion that built up while the aircraft in question were stored.

The AD reads: “Corrosion of the engine bleed air 5th stage check valve internal parts during airplane storage may cause the valve to stick in the open position. If this valve opens normally at takeoff power, it may become stuck in the open position during flight and fail to close when power is reduced at top of descent, resulting in an unrecoverable compressor stall and the inability to restart the engine.”

Possibility of dual engine failure

While losing one engine in flight is a serious emergency, it does happen from time to time. However the AD makes clear that the issue could potentially affect both engines, causing a much more serious dual engine shutdown. And the FAA determined a similar condition is likely to present itself in other aircraft.

“Corrosion of these valves on both engines could result in a dual-engine power loss without the ability to restart. This condition, if not addressed, could result in compressor stalls and dual-engine power loss without the ability to restart, which could result in a forced off-airport landing,” the text continues.

Inspections need to be made “for any airplane that is in storage on or after the date of receipt of this AD, and any airplane that, as of the date of receipt of this AD, has been operated for 10 or fewer flight cycles since returning to service from the most recent period of storage.” The FAA defines storage as any 7-day period without operation.

The full emergency AD, which outlines a series of steps to be taken beyond inspection of the valve in question, can be found here.

Further reading

A COVID-19 logistical puzzle: how airlines safely store their aircraft