Many 737 planes have been sitting in hangars for weeks as the coronavirus pandemic suppressed demand for air travel. As airlines resumed operations, they discovered that a key valve tended to get stuck after weeks of not being used. The FAA estimates that around 2,000 aircraft could be affected.
“If this valve opens normally at take-off power, it can get stuck in the open position during flight and not close when power is reduced at the top of descent,” warns the FAA directive. This could result in “an irreparable blockage of the compressor and the inability to restart the engine”.
This has happened four times in recent weeks. Alaska Airlines admitted that one of its planes suffered from the problem on a flight from Seattle to Austin. The plane was able to land safely despite an unexpected shutdown of one of its engines and no one was injured, according to the airline.
Fortunately, the same was true for the other three incidents: only one engine stopped and no injuries occurred. But the FAA fears that a plane could experience the same malfunction in both engines simultaneously, which could “result in a forced landing outside the airport.”
The FAA therefore orders airlines to carefully inspect the engines of any 737 aircraft that have been out of service for seven days or more in a row – and have not flown 10 times since. If a sticky valve is discovered, it must be replaced before the aircraft can be returned to service. Most airlines have said the mandatory inspections will not have a significant impact on their flight schedules.
The order is for older 737 models – from line 737-300 to line 737-900. Boeing’s new 737-MAX line is still anchored as the company struggles to tackle design and software issues.