N22704

A COLLISION BETWEEN THE AIRCRAFT AND THE PLATFORM DURING THE EMERGENCY AUTOROTATION WHICH CAUSED THE LEFT SKID AND FLOAT TO SEPARATE AND DESTABILIZED THE AUTOROTATION. THE COLLISION WAS PROBABLY UNADOIDABLE DUE TO THE MANEUVER THAT WAS BEING CONDUCTED AT THE ONSET OF THE EMERGENCY. THE EMERGENCY LANDING WAS ATTEMPTED FOLLOWING AN ENGINE FAILURE THAT WAS THE RESULT OF A TOTAL COMPRESSOR FAILURE. THE COMPRESSOR FAILURE WAS CAUSED BY A FATIGUE FAILURE OF THE SIXTH STAGE WHEEL WHICH SEPARATED. THE FAILURE WAS INITIATED DUE TO A CASTING INCLUSION IN THE WHEEL WHICH WAS NOT DETECTED DURING THE MANUFACTURING PROCESS.