- The CFM56 is one of the most commonly used around the world.
- United said it is already inspecting the engines because of a service bulletin.
- Southwest is speeding up testing of the engines out of "caution."
United CEO Oscar Munoz said in a quarterly earnings call that the airline had started the inspections due to a service bulletin and that the airline will be "fully compliant."
Service bulletins are issued by manufacturers, the airline said.
The CFM56-7B engine is one of the most widely used engines in the world, powering some 6,700 aircraft worldwide, according to its manufacturer, CFM International, a joint venture of General Electric and France's Safran Aircraft Engines.
CFM did not immediately respond to a request for comment about the bulletin. United has close to 700 of the engines, the airline's chief operating officer said.
Following Tuesday's engine explosion on Southwest Flight 1380, from New York to Dallas, Southwest said it would speed up ultrasonic testing of the engines and expected to complete the process within 30 days.
The engine had caught the attention of federal regulators before. The Federal Aviation Administration last year proposed more stringent testing of the engines after an uncontained engine failure in the summer of 2016 on a Southwest flight. CFM said it would send about 40 technicians to help Southwest with its inspection program.
Engines are designed with special casings to prevent shrapnel and other debris from puncturing the fuselage. Such an event is rare but occurred on the 2016 flight, when debris punctured the Southwest plane, leaving a 16-inch-long hole, according to the National Transportation Safety Board.