The Federal Aviation Administration said on Friday its order was for about 2,000 passenger jets in the United States.
The FAA said operators must inspect any 737s that have been parked for at least seven days or that have flown less than 11 times since it was returned to service. This is because of reports that some engine valves can get stuck in the open position.
Corrosion of the valves on both engines could cause a complete loss of power without the ability to restart the engines, forcing pilots to land anywhere other than an airport, the FAA said in the order dated Thursday.
Chicago-based Boeing Co. said that with airplanes stored or used less often during the coronavirus pandemic, “the valve may be more susceptible to corrosion.” The company said it was providing inspection and part replacement assistance to aircraft owners.
Large airlines typically fly their planes several times a day. However, they parked hundreds of planes when the coronavirus pandemic sparked an air travel collapse this spring and are bringing back some of those planes as passenger traffic increased slightly.
The FAA did not provide details on the four cases of engine shutdown.
Alaska Airlines said a flight occurred July 15 between Seattle and Austin, Texas, and the plane landed without incident. Alaska has said six of its planes need inspections, which have already started.
American, United and Southwest said none of their planes had valve-related engine shutdowns. American said four of its planes were in need of inspections, which were completed and found no problems. United said it was inspecting 28 planes. Southwest was in the process of determining how many planes to check.
Delta Air Lines said it would inspect 20 planes, but did not say if any of its planes suffered engine shutdowns.
The emergency order applies to versions of the 737 called NG and Classic, the latter no longer in production but remaining in some airline fleets. The directive does not apply to the new Boeing 737 Max, which has been grounded around the world since March 2019 after two accidents that killed 346 people.
Passenger jets have two or more engines, and multiple engine failures of the type the FAA warned of in its order are rare. One example is the 2009 “Miracle on the Hudson”, in which US Airways pilots landed their aircraft on the Hudson River in New York City after bird strikes destroyed both engines. All 155 people on board survived.