What happened
On 14 August 1996, a private flight involving a Robinson R2CO B, registration G-CLYV, was traveling through Killary Harbour, Co. Galway. The flight, which included the pilot and one passenger, had previously conducted several short local trips near Tully Cross. While navigating the steep-sided fjord, the aircraft began to exhibit unusual behavior, characterized by several leftward yaws. The pilot initially suspected turbulence or a potential bird strike.
As the flight continued toward the head of the fjord at a reduced speed, the aircraft experienced further yawing accompanied by sounds resembling engine backfiring. Shortly thereafter, the engine began to lose power. At an altitude of approximately 800 feet, the pilot opted to perform an emergency landing in the sea near a nearby fishing boat. The helicopter landed in approximately 3 metres of water and sank immediately. While the pilot and passenger successfully evacuated the aircraft, their exit was hindered because they were not wearing their auto-inflating life jackets, which expanded upon submersion and blocked the small cabin doors.
The investigation
The AAIU examined the wreckage following its recovery from the seabed. Investigators analyzed the engine, fuel system, and electrical components. While the engine could not be rotated due to salt deposits in the fourth cylinder, this was attributed to the post-accident immersion in seawater rather than a pre-existing mechanical failure. The investigation also looked into whether the fuel shut-off valve had been inadvertently closed by movement in the cockpit, but found no evidence to support this.
Meteorological data was reviewed to assess the risk of icing. At the time of the accident, the temperature at 800 feet was 15ºC with a dew point of 11ºC. Furthermore, the investigation looked into the functionality of the aircraft's safety equipment and the impact of the auto-inflating life jackets on the crew's ability to egress.
Findings
- The primary cause of the engine power loss was carburetor icing.
- The pilot's decision to reduce airspeed and altitude likely exacerbated the icing by increasing the temperature drop across the carburetor venturi.
- The aircraft's automatic engine speed governor may have masked the initial onset of power loss by adjusting the throttle automatically.
- The auto-inflating life jackets, while present, impeded the crew's escape from the cabin once they had inflated.
Safety action
- Pilots of light piston-engined aircraft, specifically helicopters, are advised to remain vigilant regarding carburetor icing risks, even in relatively warm temperatures.
- The Irish Aviation Authority (IAA) was encouraged to warn pilots about the egress risks associated with using auto-inflating life jackets in small aircraft.