WASHINGTON (AP) _ The Army announced Monday it was temporarily grounding its entire fleet of CH-47 Chinook transport helicopters after a crack was found in a transmission gear in one being used by the British Royal Air Force.

``The fleet is grounded. It's a precautionary measure,'' said an Army spokeswoman, Nancy Ray.

She said that 466 helicopters in the Army fleet were involved in the temporary grounding.

``In an overhaul, the Royal Air Force discovered a cracked gear. That gear has been traced diligently,'' Ray said. She said Boeing was working with the Army Aviation Center to see if the problem affected any of the Army Chinooks.

The twin-rotored Chinook helicopter is the military's medium tactical heavy-lift transport.

Meanwhile, the British Ministry of Defense said Monday that it has grounded its fleet of Royal Air Force Chinooks also, pending safety checks.

The RAF Chinooks are used in many different countries, but the exact number was not immediately available.