Boeing has grounded its 777X aircraft test fleet, after discovering damage to a structure that mounts the engine to the wing of the plane. 

According to aviation outlet The Air Current, Boeing found the damage during scheduled maintenance of one of its 777X test planes. Similar issues were then found in two other aircraft, revealing cracks in the structure that transfers thrust from the engines to the plane. Boeing has since grounded the test fleet, confirming in a statement that it plans to replace the part and resume test flights when the issue is fixed. 

Boeing 777X is billed as the world's largest twin-engine airplane, but it has been plagued by delays since it was first scheduled to enter service in 2020. Problems with the plane have ranged from issues with a supplier flagged by the Federal Aviation Administration (FAA) in 2020, to a test flight incident in 2021 where the plane unexpectedly pitched forward.

Boeing currently has orders for 481 777X planes, set to deliver sometime in 2025. It's unclear what these latest problems will mean for that timeline, or for the plane's final certification from the FAA.