WASHINGTON (Reuters) – United Airlines confirmed on Friday it has delayed the return of some grounded Boeing (NYSE:) 777 planes with Pratt & Whitney 4000 engines until at least May 12.

Shortly after takeoff from Denver on February 20, 2020, a United Airlines jet 777 engine failed. It rained debris across nearby areas but nobody was hurt and the plane returned safely to Denver.

“We continue to work conscientiously with Boeing, Pratt & Whitney and the FAA to safely return these aircraft to service soon, and our current plan will allow them to return in the second half of May,” United spokesman Joshua Freed said.