29-Nov-2013 Source: TSB
The Transportation Safety Board of Canada (TSB) today released its investigation report (A12A0085) into the August 2012 engine failure and hard landing of a Bell 407 helicopter inWabush, Newfoundland and Labrador.
On 12 August 2012, a Universal Helicopters Newfoundland Limited Bell 407 helicopter was slinging a drill tower approximately 4 nautical miles southwest of Wabush, Newfoundland and Labrador. At around 1 p.m. Atlantic Daylight Time, as the helicopter was approaching the drill base frame, the engine lost power. The helicopter then immediately descended and yawed to the left. The engine power loss occurred at an altitude from which a safe landing could not be assured, resulting in substantial helicopter damage; there was no post-crash fire. The pilot, who was the sole occupant, sustained minor injuries and was able to exit the aircraft.
The Bell 407 is powered by a single Rolls-Royce Corporation (RRC) Model 250-C47B turbine engine. A metallurgical examination of the occurrence helicopter’s engine revealed high-cycle fatigue (HCF) striations on 6 turbine wheel blades. One of these blades had an HCF crack, which propagated about 0.40 inches before it separated in overstress. The failure of the first blade led to a rapid failure of the turbine wheel as the remaining blades separated in overstress due to impact with blade fragments.
Since April 2002, there have been 3 similar occurrences of HCF blade failure on part number 6898663 third-stage turbine wheel installed in the Model 250-C47B engines. At the time of this report, RRC has not been able to specifically identify what engine operating condition, or conditions, cause the tensile residual stresses to be induced at the blade hub trailing edges.
The TSB is an independent agency that investigates marine, pipeline, railway and aviation transportation occurrences. Its sole aim is the advancement of transportation safety. It is not the function of the Board to assign fault or determine civil or criminal liability.