Leaving planes in storage for extended periods may not be doing them any good, but that is what has happened due to the coronavirus pandemic and the corresponding drop in air travel.

Unfortunately, according to the Federal Aviation Administration, storing some planes can lead to problems. In the case of about 2,000 older 737 Classic and Next Generation planes, (not the 737 Max) a critical air check valve may become corroded. That could lead to the value sticking open, which could be catastrophic. If the valves are stuck open, both of the plane’s engines could lose power without the ability to restart.

As a result, the FAA has issued an emergency air worthiness directive ordering operators of the 737 Classic and Next Generation to perform emergency inspections of all planes that have been out of operation for seven consecutive days or longer. The directive applies to airlines, owners and operators of the affected planes.

“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,” reads the directive. The condition could result in “forced off-airport landing.”

Boeing said in a statement that the valve in question is indeed more susceptible to corrosion during periods of inactivity. It is providing information about inspections and valve replacement to fleet owners when issues are discovered.

The directive was apparently prompted by four reports recently of single-engine failures related to the valve becoming stuck in the open position. Inspectors discovered corrosion on some of the air check valves. There have been no reports of accidents or injuries so far.

Consumers rely on airlines and operators to perform proper maintenance

The coronavirus pandemic has created an unusual situation, with many planes sitting empty for long periods between uses. That does not mean, however, that airlines, fleet owners and other operators of aircraft can assume that all systems are still go. As the FAA’s directive indicates, some airplane parts can degrade or become corroded over time.

If that happens, it could cause a dangerous situation or even a crash.