The FAA has issued an emergency Airworthiness
Directive (AD) after four recent reports of single-engine
shutdowns due to engine bleed air 5th stage check valves being
The emergency AD (2020-16-51) has been sent to
owners and operators of U.S.-registered Boeing 737-300, -400, -500, -600, -700,
-700C, -800, -900, and -900ER series airplanes. Around 2,000
aircraft need to be inspected.
The FAA explains the problem in the emergency AD
as, "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. 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."
Airlines have been ordered to inspect any of the
aforementioned aircraft that have been unused for 7 or more
The FAA has not given any further details of the
four recent reports, one of which is believed to be an Alaska
Airlines flight from Seattle-Tacoma International Airport (SEA) to
Austin-Bergstrom International Airport (ASU) in Texas on 15 July in which
the left engine of the Boeing 737 failed as the aircraft was
coming in to land. The plane managed to land safely and nobody was hurt.
The CFM56 engine was later replaced.
The emergency AD is available in .pdf format