Storage-related corrosion of Boeing-delivered valves on certain Boeing 737 CFM56 engine have been found to cause four-engine shutdowns. This adversity has compelled regulators to issue prompt inspection orders of 1,140 aircraft prior to their return to service after extensive grounding.
Corrosion Ultimately Causes Unrecoverable Stall
“During aircraft grounding, corrosion of the engine bleed-air fifth-stage check-valve forces the valve to stick in the open position,” stated by FAA. “This valve may get stuck in the open position in between flight if it opens normally at take-off power. Furthermore, the valve fails to close when power is reduced at top of descent. These factors disable the engine to get the start again and result in an unrecoverable compressor stall.”
Implementation of Directive
This directive of inspection is only for specific aircraft. Any aircraft that hasn’t been operated for at least seven consecutive days is subject to an inspection. The order of inspection applies to Boeing 737 (737-300s, -400s, -500s, -600s, -700s, -800s, and -900s) powered by CFM56-3s and CFm56-7s engines. The check majorly involves inspection of:-
- Manual rotation of valve flapper plates
- Bushing for cracks
- The ability of certain parts to rub with each other
However, the FAA directive does not display the associated links between the in-service incidents. Whereas, other authorities including Australia’s Civil Aviation Safety Authority and EASA have immediately followed the U.S move of inspection.
Aircraft Needed for Inspection
Reliable data illustrates there are a total 1,140 737s that require thorough inspection because they have not operated for almost seven consecutive days. Thus 2,280 Boeing 737 engines need to be inspected. The operators in the U.S own 25% of this fleet. Airlines around the world operate the rest of the aircraft. Most of them are already in long-term storage.
COVID-19 Affected Airworthiness of Aircraft
COVID-19 did not only paralyze the flight operations rather it also corroded a number of aircraft by putting them into long-lasting preservation. Throughout the globe, airliners parked their aircraft at different airfields. The versatile geographical and environmental factors contributed differently to making the fleet static for a long period. The operators are now feeling a deficiency of adequate grounding patterns of aircraft. However, manufacturers are putting hard to fill that gap. They are reminding owners of airlines from dampness to failure to safeguard different openings on aircraft from the astray animals that can affect airworthiness.