The National Transportation Safety Board said that an initial analysis of the engine on United Flight 328 showed signs of fatigue. Over the weekend, the plane was forced to make an emergency landing after the engine explode about 20 minutes after takeoff, raining debris down on a Denver suburb.
NTSB Chairman Robert Sumwalt explained that the metal fatigue caused one of the fan blades on the plane's right engine to break off and hit another blade in the engine. Investigators have taken the fan blade to a lab where they will inspect it and try to determine how long it was damaged before it failed.
Boeing announced that it was grounding all airplanes that were equipped with the Pratt & Whitney 4000 engine. That impacts 69 jets that are currently in service and 59 that are currently in storage. United Airlines is the only American carrier that has jets with that engine.
This is not the first time the engines have failed in recent years. In 2018, a fan blade broke on a United flight while it was over the Pacific Ocean. In December 2020, two fan blades broke on a flight over Japan. In both instances, the pilots managed to safely land the aircraft.
"This isn't the first time this happened," aviation expert Greg Feith told NBC's Today show.
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