Report concerning air accident at Dalamot in Ullensvang, Hordaland county in Norway on 04.07.2011, LN-OXC

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Description

As the helicopter started the descent for an approach in mountainous terrain, witnesses observed it turning tightly to the right. During the turn, control of the helicopter appeared to be lost, with high bank and 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.

The investigation has not revealed any technical defects or irregularities that could have influenced the course of events. The Accident Investigation Board Norway 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.

Three safety recommendations are issued in the report, dealing with limitations during manoeuvring with passengers on board, warning of servo transparency hazards and the need for flight recorders.

Safety recommendation

Safety recommendation SL 2012/08T

Excessive manoeuvring at low height reduces safety margins. Airlift has, following the accident, set a limit for 30 degrees roll and 15 degrees pitch at heights below 500 ft when transporting passengers. As such manoeuvring limitations are not necessarily suited for regulations, one possible measure may be to establish an industry standard.

The Accident Investigation Board Norway (AIBN) recommends that the Civil Aviation Authority, through its role as chair of the Committee for Helicopter Safety - Inland Operations, ensures that an industry standard for manoeuvring limitations is established for passenger transport.

Safety recommendation SL 2012/09T

If servo transparency is encountered in a right turn, the associated uncommanded right roll and possible pitch-up have the potential to cause a significant deviation from the intended flight path which, if encountered in close proximity to terrain or obstacles, could be hazardous.

The Accident Investigation Board Norway (AIBN) recommends that EASA requires the type certificate holder Eurocopter to issue a warning of the particular hazard when encountering servo transparency in a right turn, preferably as a permanent note in the Flight Manual of the helicopter models in question.

Safety recommendation SL 2012/10T

A flight recorder is a valuable tool for establishing what happened in an air accident. The recordings can also be utilised for training and flight safety work in general under the right conditions. The technological development has advanced far enough to make the Accident Investigation Board believe that it is time for the aviation authorities to require suitable recorders for lighter aircraft as well, including light helicopters.

The Accident Investigation Board Norway (AIBN) recommends that EASA considers introducing requirements for flight recorders on more aircraft than those covered by the current regulations.

Location
Dalamot in Ullensvang, Hordaland county
Occurrence date
04.07.2011
Aircraft
Eurocopter AS350 Ecureuil
Registration
LN-OXC
Meteorological conditions
VMC
County
Hordaland
Type of occurrence
Accident
Type of operation
Commercial, other
Category of operation
Light, helicopter (<= 2 250kg)
Aircraft category
Helicopter, Single-engine, Turboprop/turboshaft
FIR/AOR
ENSV (Stavanger ATCC)
Skriv ut
Reports same aircraft model
Reports same category of operation