Boeing said Monday that it has paused flight tests of its 777X after it found damage in a structure of one of the wide-body aircraft.

The company said it discovered the damage to the custom part, which it said is between the engine and the airplane structure, during scheduled maintenance. It has since grounded the three other 777-9 airplanes in its test fleet. No other flight testing was scheduled for the other aircraft, Boeing said.

“Our team is replacing the part and capturing any learnings from the component and will resume flight testing when ready,” Boeing said in a statement. It said it has informed the Federal Aviation Administration and its customers, which have ordered 481 of the 777X, according to Boeing’s website.

It wasn’t immediately clear whether the grounding and issue would impact certification and delivery of the new wide-body jetliners, which are slated for 2025, about five years behind schedule. Boeing began flight tests of the aircraft with the Federal Aviation Administration in July, a major milestone.

The news, reported earlier by The Air Current, comes as Boeing’s leaders, including new CEO Kelly Ortberg, are trying to move the company past a safety crisis that started with a doorplug blowout at the start of the year.