ASN Wikibase Occurrence # 137259
Last updated: 22 May 2013
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Narrative:The helicopter was used to transport people to a cabin site in the mountains. The weather was good with fine flying conditions. The first flight with five passengers had been completed. There were four passengers on board during the second flight. As the helicopter started the descent towards the cabin site, the passengers of the first flight witnessed the helicopter turning tightly to the right. The witnesses have explained that during the turn, control of the helicopter appeared to be lost with an estimated bank angle of 60-90 degrees in a steep descent. At the end, it seemed as if control was about to be regained, but the helicopter hit the ground hard about 500 metres short of the planned landing site and immediately caught fire. All five persons on board were fatally injured. The helicopter was a total loss.
Eurocopter AS 350B3 Ecureuil
|Operator:||Airlift AS (operator) Blueway Helicopter AS (owner)|
|C/n / msn:|| 4260|
|Fatalities:||Fatalities: 5 / Occupants: 5|
|Airplane damage:|| Written off (damaged beyond repair)|
|Location:||At Vassli Ullensvang between Dalamot and Busete in Hardanger, Hordalan -
|Phase:|| En route|
The forward speed at ground impact has been calculated to about 105 kt (194 km/h) based on tracks at the accident site. The helicopter hit the ground with a nearly flat pitch angle and about 45° of bank to the right. The investigation has not revealed any technical defects or irregularities that could have influenced the course of events. The extensive fire damage made parts of the helicopter unavailable for examination, but it was possible to establish that the engine was delivering power to the rotors when the accident happened. It was also possible to verify that key parts of the flight controls were intact prior to ground impact.
The AIBN considers it likely that abrupt manoeuvring initiated a sequence where control of the helicopter was partly lost for a period, and that the height was insufficient for the commander to recover in time.
The AIBN believes that the hydraulic system may have reached its limitation during the manoeuvring, resulting in the phenomenon servo transparency, (also called jack stall) occurring. When this phenomenon occurs in a right turn, it can cause the helicopter to deviate substantially from the intended flight path and simultaneously counter the pilot's efforts to recover. The AIBN believes that warnings about this hazard should be made clearer in the Rotorcraft Flight Manual. This type of helicopter has no warning light or other means to provide warning of imminent servo overload. In addition to high mass, high speed and high torque, high density altitude (‘thin air’) are among the factors that precipitate overload. This means that servo transparency will occur more easily when flying a heavily loaded helicopter in the mountains on a hot day, as the case was with LN-OXC.
It is not possible to conclude with certainty what flight attitudes and loads the helicopter was subjected to, which airspeed it held and the flight path it followed in the turn preceding the crash. Current regulations do not require use of flight recorders in light aircraft. The Accident Investigation Board believes that the time has come to utilise available, light flight recorders to provide a better data basis for accident investigations and other safety enhancing activities.
http://mobil.tv2.no/nyheter/innenriks/fem-fryktes-doede-i-helikopterstyrt-i-hardanger-3532789.html http://www.vg.no/nyheter/innenriks/artikkel.php?artid=10096541 http://www.vg.no/nyheter/innenriks/artikkel.php?artid=10080177 http://www.jetphotos.net/viewphoto.php?id=7069680
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