The U.S. military grounded its fleet of Lockheed Martin F-35 Joint Strike Fighters after a routine engine inspection revealed a cracked turbine blade in an F-35A based at Edwards Air Force Base, Calif. The precautionary flight suspension was announced on February 22, following an inspection earlier in the week. The grounding affects all three variants of the fighter, for a total of 51 aircraft.

Only recently, the F-35B short takeoff/vertical landing (Stovl) variant ordered by the U.S. Marine Corps was cleared to resume flying after being grounded for more than three weeks when an improperly crimped fueldraulic line was discovered in a test aircraft at Eglin AFB, Fla. The flight clearance was announced on February 12.

In a brief statement, the Department of Defense said the cracked turbine blade was discovered in the Pratt & Whitney F135 engine installed in aircraft AF-2, an F-35A conventional takeoff variant, at Edwards AFB. The engine’s turbine module and associated hardware were shipped to Pratt & Whitney’s engine facility in Middletown, Conn., for more thorough evaluation.

“As a precautionary measure, all F-35 flight operations have been suspended until the investigation is complete,” the Pentagon said. “It is too early to know the fleet-wide impact of the recent finding. The F-35 Joint Program Office is working closely with Pratt & Whitney and Lockheed Martin at all F-35 locations to ensure the integrity of the engine, and to return the fleet safely to flight as soon as possible.”