AS350BA during Finland's Neste Rally 2016. Photo by Tiia Monto
The Australian Transport Safety Bureau has released its final report on the 2015 emergency landing of a Eurocopter/Airbus Helicopters AS350 BA. One of the findings pointed to a failure of the Tubromeca/Safran Helicopter Engines Arriel 1B engine.
The bureau said the helicopter, registered VH-SFX, was on a mission to identify noxious plants in dense forests in Queensland Nov. 2, 2015. To perform the task, the aircraft needed to operate at a low altitude and airspeed. During its fourth flight of the day, the bureau said the helicopter momentarily yawed twice in an “uncommanded and unusual way.” The pilot then ceased the operation, climbed and increased forward airspeed. The aircraft then headed back toward the base. Before arrival, the chip detector light came on, prompting the pilot to search for a suitable landing area, the bureau said. As the helicopter continued to climb, the engine stopped producing power. The pilot was able to land the aircraft using an emergency autorotation. The three passengers received no injuries or minor injuries, and the pilot sustained “serious” back injuries, according to the bureau. The helicopter also sustained substantial damage.
The bureau’s findings include:
- “The helicopter lost power due to a failure of the Arriel 1B engine. The failure was a result of coke particles that had clogged the front oil jet from the power turbine shaft, preventing oil flow, and leading to a total seizure of the front bearing. The specific source that led to the coke formation and oil clogging of the front oil jet could not be determined.
- “The rear-splined rear nut had not been adhesively bonded to the power turbine shaft, as required. When the front bearing failed, the lack of adhesive led to a progressive tightening of the nut and additional frictional heating of the shaft from contact with the static engine components. The consequential reduction in material strength from the heating allowed the power turbine shaft to fracture and the disc to separate, further increasing the severity of the engine failure.
- "The helicopter was not fitted with energy absorbing front seats, which may have reduced the risk of injury to occupants during an accident."
In response, the bureau said Safran Helicopter Engines amended its procedure manual to include systematic cleaning of the power turbine front bearing assembly oil jet and oil jet supply pipe. The company has also initiated a number of training and process changes to ensure the adhesive bonding between the power turbine and the rear nut is maintained during service.