The U.S.’ Federal Aviation Authority (FAA) issued an Airworthiness Directive on Friday for 2,000 U.S. registered Boeing 737 NGs and Classics. Engines of 737s that have been idle for a long time may fail in flight.
Boeing 737s that have been continuously idle for more than a week can show signs of corrosion on small valves inside of the engines. This could have an effect on the fuel supply, possibly causing one or both engines to fail. According to the FAA, it is possible that in such a case both engines will refuse to restart.
The FAA recommends that airlines inspect their 737s for corrosion inside the engine before returning it into service. Boeing indicates that the aircraft’s engine valves are indeed more sensitive to corrosion when the aircraft is stationary.
In order to avoid such maintenance costs, airlines often store their planes in dry, desert-like environments. For example, part of the Singapore Airlines fleet has been stored in an Australian desert. Other airlines, such as Ryanair, choose to fly empty aircraft a few times, meaning that that less maintenance is required when the aircraft is put back into service.