ATSB publishes final report on Squirrel engine failure

An image of the AS350BA Squirrel, VH-SFX, involved in the incident. (ATSB)
An image of the AS350BA Squirrel, VH-SFX, involved in the incident. (ATSB)

The Australian Transport Safety Bureau (ATSB) has released its final report into the engine failure and forced landing of AS350BA Squirrel, VH-SFX, which occurred over dense forest in the Whyanbeel Valley, Queensland on 2 November 2015.

While conducting a low-altitude aerial weed spotting operation, the helicopter yawed twice in an uncommanded manner. In response, the pilot climbed and increased the helicopter’s forward airspeed and attempted to return to base. However, the engine failed and the pilot to conducted an autorotation landing.

The helicopter landed heavily with the skids digging into the uneven terrain and breaking off, but remained upright. The helicopter was not fitted with energy absorbing front seats which may have reduced the risk of injury to the navigator in the front and the pilot who both received injuries from the impact forces.

Analysis of the engine identified that the Squirrel lost power to its Arriel 1B engine due to a front bearing failure in the turbine module. The failure was due to an accumulation of coke particles in an oil jet. The ATSB it was unable to conclude specifically why the coke particles had formed.

The severity of the engine failure was increased through the fracture of the power turbine shaft and the subsequent separation of the turbine disc due to a lack of adhesive on the splined nut that was threaded to the rear of the power turbine shaft.

The engine manufacturer, Safran Helicopter Engines, has amended its procedure manual to include systematic cleaning of the power turbine front bearing assembly oil jet and oil jet supply pipe. Safran HE 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.

The ATSB said the emergency landing was handled in a competent and proficient manner. The pilot’s pre-departure briefing gave the passengers the necessary knowledge to prepare for the emergency by adopting the brace position and exiting the helicopter only when it was safe to do so. The Bureau also said its investigation highlighted the response to an abnormal operation in a timely and proficient manner can minimise the consequences of an accident.