What happened
On 16 September 2014, an Agusta Bell 206B Jet Ranger II, registration G-SUEX, was conducting a transit flight along the Yorkshire coast. The helicopter, operated as public transport, was flying at a very low altitude near Flamborough Head. Earlier in the day, the pilot had landed in a field near Robin Hood’s Bay to wait out poor weather conditions before resuming the flight toward Humberside Airport.
During the final stage of the flight, the helicopter was observed flying offshore, at a height roughly level with the 200-foot cliff tops. Eyewitnesses noted that the aircraft appeared to turn briefly away from the cliffs before making an abrupt turn back toward the land and descending steeply. The helicopter struck the surface of the sea at the base of the cliffs. The impact resulted in two fatalities, involving both the pilot and the passenger.
The investigation
Investigators examined radar data, which showed the aircraft had been operating at altitudes as low as 30 to 130 feet above sea level during parts of its transit. Audio analysis of a witness's video recording provided critical evidence; frequency analysis of the rotor sounds revealed a significant decay in rotor RPM. This decay was inconsistent with a standard autorotation maneuver and instead suggested a technique used to maintain altitude following power loss.
Technical examination of the wreckage was complicated by the aircraft's immersion in seawater and subsequent wave action. However, investigators focused on the engine's turbine assembly. They discovered severe thermal distress in several bearings, including the No. 5 and No. 8 bearings. While the engine's gas generator was still rotating at the time of the accident—as evidenced by seaweed found within the compressor—the degradation of the power turbine assembly had removed drive from the rotor system.
Findings
- The primary cause of the accident was the failure of bearings within the turbine assembly, which led to a loss of engine power.
- The pilot was flying at a low altitude offshore, a position that left no margin for error in the event of an engine failure.
- The helicopter was not equipped with emergency flotation equipment, and the flight was conducted beyond the autorotative distance of land.
- Due to the decay in rotor RPM, the pilot was unable to successfully flare the aircraft or achieve a controlled descent, leading to a high-energy vertical impact with the sea.