N355EH
AEROSPATIALE AS-355F-1
ACFT WAS DEPARTING AN ELEVATED HELIDECK ON AN OFFSHORE PRODUCTION PLATFORM WHEN IT EXPERIENCED A COMPLETE LOSS OF TAIL ROTOR THRUST AND ACFT CONTROL DUE TO A FAILURE OF THE TAIL ROTOR DRIVE SHAFT. THE FAILURE OCCURRED AS THE PLT INITIATED HIS TAKEOFF WITH THE ACFT HAVING JUST CLEARED THE DECK AND RECOVERY WAS NOT POSSIBLE. INVESTIGATION REVEALED THAT THE DRIVE SHAFT HAD FAILED AS A RESULT OF FATIGUE CRACKING IN AN AREA OF FRETTING WHERE THE SHAFT WAS BONDED AND BOLTED TO ITS COUPLING. THIS AND PREVIOUS FAILURES IN THE SAME AREA INDICATED THAT THE SHAFT WAS UNDER DESIGNED FOR THE APPLICATION AND NORMAL OPERATING STRESSES. SHAFT WAS SUBSEQUENTLY RE-DESIGNED AND THE FLEET RETROFITTED.
THE LOSS OF CONTROL OF THE AIRCRAFT WHICH OCCURRED WHEN THE TAIL ROTOR DRIVE SHAFT EXPERIENCED A FATIGUE INDUCED MATERIAL FAILURE AND TAIL ROTOR THRUST WAS LOST. EVIDENCE INDICATED THAT THE SHAFT WAS UNDER DESIGNED FOR THE LOADS THAT WERE ENCOUNTERED DURING NORMAL OPERATIONS.
Source: NTSB Aviation Accident Database
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