C8/2007L Helicopter accident at Kangasniemi 8 November 2007

An accident occurred at 10:05 on Thursday, 8 November 2007 at Koittila in Kangasniemi municipality. A Hughes 369D helicopter, registration OH-HLA, collided with the ground. The helicopter in question was maintaining a transmission line by sawing tree branches off with an external saw. The pilot, the sole occupant of the helicopter, was slightly injured, however, the helicopter was completely destroyed. On 8 Nov 2007 Accident Investigation Board Finland (AIB) appointed investigation commission C8/2007L for this accident. Investigator Juhani Hipeli was named investigator-in-charge and Investigator Risto Nyqvist as a member of the commission. On 20 Nov 2007 AIB revised the decision by relieving Investigator Risto Nyqvist from his duties. Concurrently, Major Jari Multanen and Captain Rauno Purho were appointed as members of the investigation commission.

The helicopter departed for the sawing flight approximately one hour and thirty minutes prior to the accident. The helicopter was fitted with a 369 kg heavy external saw that extended 25 m below it. During the flight it was snowing lightly. At times the snowfall turned into heavy sleet, with snow accumulating a few centimetres on the ground. After flying for about an hour the helicopter landed for hot refuelling. After the helicopter became airborne again it continued the sawing operation in light snowfall. While the helicopter was sawing branches in an almost completely stationary hover the engine failed. Because of the external load and the steering input of the pilot there was not a controlled descent, but rather, pivoting around the saw boom, the helicopter yawed into the direction it had come from, collided with trees and finally crashed into the ground. In spite of his injuries and the damage to the helicopter the pilot made it out of the cabin on his own accord.

It is known that a jet engine such as the one used in this helicopter may flame out if it ingests enough snow or ice. The engine manufacturer has advised users of this propensity by publishing bulletins explaining the phenomenon. The company had fitted the helicopter with a particle separator at the air inlet and issued restrictions concerning snowfall in order to ensure the safe conduct of helicopter operations. When it was sleeting the heaviest the meteorological conditions did not fulfil the company’s weather requirements. While the helicopter was aloft snow and sleet probably built up in the air intake, particularly, during heavy snowfall and sleet. Without warning, the engine probably ingested snow from the air intake, resulting in a flame-out. The helicopter was equipped with an engine warning system that also activates an automatic reignition system, thereby providing an automatic engine restart capability. During the accident flight the system was switched off, which is a violation of the helicopter Flight Manual. Moreover, the investigation revealed that there were shortcomings in the company’s operations manuals and that the personnel do not always comply with valid regulations.

The accident was caused by flying in inclement weather, snowfall, which resulted in an engine flame-out that was probably caused by the engine ingesting wet snow accumulated on the engine air intake surface. The fact that the engine warning system was turned off, effectively eliminating the automatic reignition system, was a contributing factor.

The investigation commission recommended that the company update the weather restrictions in its operation manuals so as to correspond with regulations. In addition, the commission recommended that the company take appropriate actions to bring the fleet’s Flight Manuals up to date as well as alter the practices of its staff so as to comply with valid manuals and regulations. The commission also recommended increased supervision with regard to staff procedures.

C8/2007L Report (pdf, 1.07 Mt)