Investigation Summary
Flight 23R was a routine shuttle service transporting oil workers from the North Alwyn and Borgsten Dolphin platforms to Sumburgh for refueling. During the approach to Runway 09 at Sumburgh, the helicopter was flying in conditions of mist and a light breeze. The crew was performing a non-precision approach, which required manual monitoring of the vertical profile and airspeed. Data from the flight recorders indicated that the engines remained powered until impact, ruling out a mechanical power loss. Instead, the airspeed was allowed to drop below the recommended minimums. As the speed decayed, the helicopter entered a high rate of descent. The manufacturer's analysis suggested the aircraft may have entered a vortex ring state at low altitude, a condition where the helicopter settles into its own downwash, making the impact unavoidable. Upon hitting the water, the helicopter inverted, complicating the evacuation for the 16 passengers and two crew members.
Final Conclusions
The inquiry led by Sheriff Principal Derek Pyle, concluded in October 2020, determined the crash was predominantly caused by pilot error. The crew failed to maintain the required airspeed during the final stages of the approach, leading to an unstabilized flight path and a catastrophic loss of altitude. The AAIB earlier reported in September 2013 that there was no evidence of a causal technical failure.
Photographic Evidence (1)
Video Analysis
No video analysis linked for this case file yet.
Crew Experience
Commander / Pilot Flying
The commander was the Pilot Flying (PF) during the accident sector. He had significant experience but relatively low hours on the AS332 L2 variant.
Co-pilot / Pilot Monitoring
The co-pilot was responsible for monitoring the vertical flightpath and seeking visual references.
Systems & Failure Modes
Flight Instruments
The crew failed to monitor the airspeed and altitude indicators, allowing the helicopter to deviate from the safe approach profile.
Vortex Ring State (VRS)
An aerodynamic condition where a helicopter's rotor system becomes engulfed in its own downwash, causing a rapid loss of lift; investigators believe this occurred at a low altitude.
Interesting Facts
- 01The helicopter engines were found to be delivering power until the moment of impact.
- 02The aircraft was found broken into several pieces against rocks at the base of the cliffs at Garths Ness, Fitful Head.
- 03The accident led to a temporary global grounding of the Super Puma L2 fleet by CHC Scotia.
- 04Visibility was restricted by mist at the time of the approach.
- 05The investigation found no evidence of a technical failure contributing to the accident.
Safety Actions & Advisories
Fleet Grounding
Source ↗CHC Scotia and other North Sea operators temporarily suspended Super Puma operations (L, L1, L2, and EC225 variants) following the crash to assess potential systemic risks.
Safety Inquiry
The UK Transport Select Committee launched an inquiry into the safety of offshore helicopter operations in the North Sea in September 2013.
Instrument Scan Training
Source ↗The AAIB recommended that EASA and the CAA review and amend training requirements to ensure pilots develop and maintain effective instrument scan techniques during automated and manual flight (Recommendation 2016-001).
HTAWS Improvements
Source ↗Recommendation 2016-012 called for the development of Helicopter Terrain Awareness and Warning Systems (HTAWS) that provide earlier warnings of a high rate of descent at low airspeed.
Side-Floating Flotation Systems
Source ↗Recommendation 2016-019 advised EASA to require that helicopters used in offshore operations are equipped with flotation systems that provide side-floating capability to improve survivability after ditching.