US FAA issues emergency Airworthiness Directive for Boeing 737 NGs, Classics in storage

Washington DC [USA], July 25 : The US Federal Aviation Administration (FAA) has ordered airlines to carry out additional inspections on any Boeing 737 NG and Classic aircraft kept in storage for more than a week, an emergency Airworthiness Directive (AD) said on Friday.
The FAA directive covers Boeing Company models 737-300, -400, -500, -600, -700, -700C, -800, -900, and -900ER series airplanes.
Post the directive, Boeing issued a statement saying, "Out of an abundance of caution, Boeing has advised operators of 737 Classic airplanes (series -300 to -500) and Next-Generation 737s (series -600 to -900) to inspect an engine valve for corrosion. With airplanes being stored or used infrequently due to lower demand during the COVID-19 pandemic, the valve can be more susceptible to corrosion."

"Boeing is providing inspection and replacement information to fleet owners if they find an issue," the statement added.
The FAA, in its directive, said, "This emergency AD was prompted by four recent reports of single-engine shutdowns due to engine bleed air fifth stage check valves being stuck open. Corrosion of the engine bleed air fifth 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," it added.
The FAA ordered the airlines to conduct multiple inspections of the suspect valves before flying planes taken from storage.