Helicopter Destroyed in Mourne Mountains After Downwind Approach

Casualties unknown • 31 nm south of Belfast Aldergrove Airport, Northern Ireland, GB

An AS355F2 Twin Squirrel crashed in Northern Ireland during a police transport mission, resulting in the destruction of the aircraft but no fatalities.

What happened

On 28 October 2010, an AS355F2 Twin Squirrel, registration G-SEWP, was performing a commercial passenger transport task for the Police Service of Northern Ireland. The mission involved ferrying personnel and equipment to a hilltop site in the Mourne Mountains. While attempting to land near the summit of Shanlieve hill, the helicopter experienced a sudden loss of lift and began a rapid descent.

During the final approach, the pilot believed the aircraft was flying into the wind; however, evidence suggests the helicopter was actually travelling largely downwind. The aircraft struck the ground short of the intended landing site, passing through a substantial stone wall. The impact caused the helicopter to bounce and break up, eventually coming to rest in an inverted position. Despite the destruction of the aircraft, the pilot, observer, and three passengers escaped with only minor injuries.

The investigation

The AAIB investigation examined the wreckage, engine components, and flight controls. Mechanical examinations of the engines, transmission, and hydraulic systems revealed no evidence of failure prior to the impact. Both engines showed evidence of ingesting wet peat, which was consistent with the aircraft being buried in the soft ground after the crash.

Investigators also reviewed meteorological data and pilot records. While the pilot had completed all required training, it was noted that he had recently suffered a family bereavement, a fact he had not disclosed to his employer. The investigation also looked into the possibility of Vortex Ring State (VRS), a phenomenon where a helicopter loses lift due to descending into its own rotor wash.

Findings

  • The pilot's error in perceiving the wind direction led to a downwind approach, which significantly increased the difficulty of the landing.
  • The helicopter was likely caught in a state of Vortex Ring State following an application of power intended to arrest the descent.
  • Deteriorating weather, including changing visual references and the approach of a warm front, may have contributed to the accident.
  • The recent personal bereavement of the pilot was considered a significant contributory factor due to the potential for increased stress and reduced concentration.

Probable cause

The accident was caused by the pilot attempting a downwind approach due to a misperception of wind direction, which likely led to the onset of Vortex Ring State during the final descent.

Frequently asked questions

What happened in the 2010-10-28 AS355F2 Twin Squirrel accident near 31 nm south of Belfast Aldergrove Airport, Northern Ireland, GB?

An AS355F2 Twin Squirrel crashed in Northern Ireland during a police transport mission, resulting in the destruction of the aircraft but no fatalities.

What aircraft was involved and where did it happen?

The accident on 2010-10-28 involved a AS355F2 Twin Squirrel, registration G-SEWP, at 31 nm south of Belfast Aldergrove Airport, Northern Ireland, GB.

What was the probable cause of the accident?

The accident was caused by the pilot attempting a downwind approach due to a misperception of wind direction, which likely led to the onset of Vortex Ring State during the final descent.

Loading the flight search…