The Federal Aviation Administration (FAA) has issued an emergency airworthiness directive for all Boeing 737 Classic and 737 Next Generation aircraft following four inflight engine shutdowns on 737’s returning to flight after storage.
The directive warns that aircraft that have been stored for more than seven consecutive days could have corrosion on the Bleed Air 5th stage check valve.
According to the FAA this could result in a double engine shutdown and a “forced off-airport” landing.
The directive says all airlines should inspect the valve, in particular the flapper plate. It says “If the flapper plate moves smoothly, without signs of binding or sticking, from the fully closed position to the stop tube using gravity force alone, the engine bleed air fifth stage check valve has passed this inspection,”
All Boeing 737s with CFM56-3 & -7 aircraft are covered by the directive.