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Final Report

Summary

What happened

On the afternoon of 2 November 2015, a Eurocopter AS350-BA helicopter, registered VH-SFX, was performing a low-altitude aerial weed spotting operation over dense forest in the Whyanbeel Valley, Queensland. On board the helicopter were the pilot, a navigator and two aerial spotters.

While conducting the work, 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 his base of operations. Subsequently, the engine failed, which required the pilot to conduct an autorotation and emergency landing.

The passengers adopted the brace position and the helicopter landed heavily with the skids digging into the uneven terrain and breaking off. The navigator in the front seat received minor injuries and the pilot received serious back injuries from the impact forces.

What the ATSB found

The ATSB found that the emergency landing was handled in a competent and proficient manner. The 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.

Analysis of the engine identified that the aircraft lost power 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 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. This was due to a lack of adhesive on the splined nut that was threaded to the rear of the power turbine shaft.

A service information bulletin issued by the helicopter manufacturer in 2010 recommended that AS350 helicopter operators consider the safety benefits of installing energy-absorbing seats. Had these seats been installed, the forces imparted to the pilot during the accident sequence may have been reduced.

What's been done as a result

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

Safety message

This investigation highlights that responding to an emergency in a timely and proficient manner can minimise the consequences of an accident. Similarly, providing emergency procedures briefings enables passengers to react appropriately in an emergency.

In this occurrence, the reason for the engine oil jet coking leading to the engine failure was not specifically determined. However, a range of factors can affect engine oil coking. These factors should be considered to ensure normal ongoing engine operation.

The occurrence

Context

Safety analysis

Findings

Safety issues and actions

Sources and submissions

 
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