FAA requires additional Boeing 737 Post-storage inspections

An American Airlines Boeing 737-800 at Phoenix. Photo by Cole McAndrew | AeroNewsX

The United States Federal Aviation Administration (FAA) yesterday issued an airworthiness directive, requiring US operators of the Boeing 737 family of aircraft to inspect the bleed air valves of their aircraft if they have previously been in storage during the COVID-19 pandemic before they are returned to service.

The Airworthiness Directive released by the FAA, the aviation industry regulator within the United States of America (USA), affects all US operators of Boeing 737 aircraft fitted with CFM International CFM-56 engines, meaning operators with Boeing 737 Classic (-300/-400/-500) or Boeing 737 Next Generation aircraft (-600/-700/-800/-900) in their fleet are now required to follow the directive before they return their stored aircraft to service. There are estimated to be 2000 Boeing 737 aircraft under FAA jurisdiction which will require inspections.

The Airworthiness Directive numbered Emergency Airworthiness Directive AD 2020-51 relates to the 5th state check valve fitted to the CFM-56 engines. According to the FAA, corrosion of the 5th stage check valve's internal parts may cause the valve to become stuck in the open position. The FAA also cautions that if the valve opens normally at take-off power, it may become stuck open during the course of the flight and fail to close at the top of the descent when power is reduced as is designed to. When the valve fails to close, the engine subsequently fails. If valves in both of an aircrafts engines happened to fail, there are fears it may lead to a catastrophic dual engine failure.

The announcement comes after a spate of four single-engine shutdowns on Boeing 737 aircraft due to 5th stage check valves being stuck open. This is due to corrosion in the 5th stage bleed air check valve mentioned above which accumulated during lengthy storage periods of aircraft due to the COVID-19 pandemic. According to the aircraft's manufacturer Boeing, "With airplanes being stored or used infrequently due to lower demand during the COVID-19 pandemic, the valve can be more susceptible to corrosion." The manufacturer also stated it would be providing operators of the aircraft with inspection and replacement operation.

Following this directive, the Indian Directorate General of Civil Aviation (DGCA) required the same check to be performed by carriers in the country with the aircraft in their fleet, including SpiceJet, Vistara, and Air India Express.