What happened
At 1520 Pacific daylight time, a Helijet Sikorsky S-61N/SP helicopter, registration not provided, was preparing for a visual flight rules flight from the Vancouver Harbour helipad to Victoria. The aircraft was carrying 15 passengers and three crew members. As the pilot applied takeoff power and the helicopter reached approximately 30 feet above the deck, the No 2 engine experienced a sudden loss of power and a significant torque split between the engines. The pilot immediately rejected the takeoff and landed the aircraft on the northern edge of the helipad with one engine inoperative. No injuries or initial damage were reported.
Following the landing, the crew secured the No 2 engine, which had shut down automatically. While attempting to taxi the aircraft forward to better align the airstair door for passenger disembarkation, the tail wheel ran off the edge of the helipad deck. This caused the rear of the fuselage to strike the deck edge, resulting in damage to the aft section of the hull. The crew eventually managed to deplane the passengers and move the aircraft to the eastern side of the pad.
The investigation
Investigators examined the No 2 engine and its fuel control unit, finding no defects or malfunctions in their operation. However, an examination of the main-rotor gearbox revealed that the No 2 input freewheel unit (IFWU) gear housing was worn well beyond allowable tolerances. The internal dimensions of the housing were found to be larger than the maximum permitted limit and exhibited eccentric wear.
The investigation also reviewed the operator's standard operating procedures. It was noted that the operator had not implemented certain engine starting and engagement procedures previously recommended by the manufacturer to reduce wear on the IFWU. Specifically, the practice of starting the No 1 engine first and then engaging the rotor, as well as certain single-engine training techniques, frequently exposed the No 2 IFWU to an overrun condition.
Findings
- The No 2 input freewheel unit (IFWU) in the main-rotor gearbox was worn beyond limits, causing it to slip under high power loading during takeoff.
- This slippage triggered an automatic overspeed and subsequent shutdown of the No 2 engine.
- Accelerated wear in the IFWU was likely caused by a combination of frequent overrunning of the same unit, specific rotor engagement techniques, and frequent single-engine training operations.
- The operator's standard operating practices at the time contributed to the premature wear of the component.