The Japan Transport Safety Board (JTSB) issued safety recommendations to Transport Canada as a result of their investigation into a serious incident involving a DHC-8 engine failure.
On March 25, 2009 a DHC-8-402, registered JA847C, operated by Japan Air Commuter as regularly scheduled Flight 3760, took off from Tanegashima Airport (TNE). While the aircraft was climbing an abnormal noise emanated from the No. 1 engine and instrument indications showed the occurrence of engine failure. The engine was then shut down and the aircraft requested emergency landing clearance from the Kagoshima Radar Approach Control Facility. The aircraft landed safely at Kagoshima Airport.
JTSB concluded that it is highly probable that, while the aircraft was climbing after takeoff, the RGB helical input gearshaft of the No. 1 Pratt & Whitney Canada PW150A engine sustained fatigue fracture and was detached from its position; the fragments of the broken shaft then flew off, damaging the engine case and breaking the blades of the HPT and the blades and vanes of the LPT and PT at the downstream stages, and this resulted in breakdown of the engine. With regard to the fatigue fracture of the RGB helical input gearshaft, it is considered probable that fatigue cracks had started from the impurity inclusion present in the metal stock of the helical gear developed in the shaft, and after undergoing repetitive application of stress, the shaft was finally fractured.
In view of this serious incident, the Japan Transport Safety Board recommends that Transport Canada give careful consideration to the following and take necessary measures thereof:
(1) Considering the detrimental effect on safety brought about by the inclusion of impurities in the RGB helical input gearshaft of the engine involved in this serious incident, P&WC, the manufacturer of the engine, should make company-wide efforts including the management of the metal stock supplier and component manufacturer serving P&WC, towards improved quality control concerning the production of the RGB helical input
(2) P&WC assigned a hazard severity of “Significant – Level 3” to this serious incident by considering only the occurrence of an IFSD as the basis for the risk level determination, but the actual conditions included the loss of all functions of the feathering system for the propeller of the shutdown engine in addition to the engine in IFSD.
The risk assessment of this serious incident should not be made only on the engine necessitating an IFSD, but instead the incident must be reassessed from the viewpoint of the safety of the entire aircraft, and safety improvement actions should be taken if the results of the reassessment indicate this to be necessary.