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The Navy and Marine Corps have ordered about 250 of their FA18 Hornet fighter jets grounded because of potential engine fires that were blamed for three crashes and suspected as the cause of a fourth crash on Monday, according to Pentagon officials.

"The flight restriction is necessary to reduce the risk of further aircraft loss due to uncontained titanium fires" in the engines, the Navy said.

The Navy has been investigating problems with the General Electric F404 engines after crashes were caused when blades in the engines' high pressure compressor broke, causing internal fires that burned through the engine casings and into flight control and other nearby systems, Navy officials said.

A West Coast Navy official said the decision, announced yesterday, to ground about 250 of the 384 Hornets in active service came after the crash Monday of a Marine Hornet in California. Although the cause of that crash has not been officially determined, it is believed to have been caused by the same type of engine problems that led to three previous crashes, the official said.

Navy officials said no pilots have been killed in any of the crashes.

The Hornet is a twin-engine tactical aircraft used by the Navy and Marine Corps as fighter escorts and for air defense of naval fleets. The planes, which cost about $32.7 million each, also can be used as strike fighters.

A California Navy official involved in the Hornet program said the grounding of the planes involves most of the aircraft assigned to the carrier USS Coral Sea in the Mediterranean and a few craft assigned to the carrier USS Midway in the Northern Arabian Sea.

"If operational necessity dictates, FA18s are fully capable of responding to any threat," the Navy said in a prepared statement.

The "flight restrictions" were issued for all engines with more than 800 hours flight time, the Navy said. Navy officials said they believe that from one-third to one-half of the 1,000 operational and spare F404 engines would be affected.

Navy officials said the flawed parts of the engines are being redesigned and tested. Officials said it has not yet been determined whether the Navy or General Electric will absorb the cost of the redesign and the repairs.

Both the blades and the casings in the engine are made of titanium, officials said. "When they {the blades} come apart, they fly like missiles," one official said.

Canada recently refused to accept delivery of an order of the fighters from McDonnell Douglas because of the same problems in the General Electric engines after the crash of a Canadian plane.