What happened
On 31 October 2012, a Eurocopter AS350 B3, registration ZS-HDI, was participating in a formation flight with two Robinson R44 helicopters. The flight, which was part of a private holiday trip, had traveled from South Africa to Botswana. After completing customs and immigration formalities at Francistown Airport, the aircraft was refueled and prepared for departure to Jacks Camp.
At 11:15 UTC, the helicopter took off as the final aircraft in the formation. Shortly after lift-off, the aircraft was hit by a sudden gust of wind. This wind event caused the tail rotor to strike an aluminum refueling ladder that was positioned near the fuel bay. The impact caused the rotor blades to disintegrate, leading to a total loss of control. The helicopter entered a spiral descent and crashed beside the refueling bay, resulting in substantial damage to the main rotor blades, the fuselage, the boom, and the tail rotor assembly. The two occupants on board escaped without injury.
The investigation
Investigators examined the aircraft's engine and digital flight data, including the VEMD and DECU, which were sent to France for analysis. The data download confirmed that there were no engine failures or power losses prior to the impact. Metallurgical analysis of the tail rotor transmission assembly was also conducted using scanning electron microscopy.
Physical examination of the tail rotor components, specifically the blade pitch control rods, revealed fractures and impact marks. The analysis of the fracture surfaces indicated a ductile failure caused by a single, massive overload. This finding was consistent with the tail rotor striking a hard object while the engine was producing power.
Findings
- The primary cause of the accident was the tail rotor striking a hard object (the refueling ladder).
- The pilot had only completed a type conversion for the AS350 one day prior to the accident, representing a lack of sufficient experience on the specific aircraft type.
- Prevailing strong easterly winds likely contributed to a lack of tail rotor effectiveness (LTE) during the critical moments of lift-off.
- The aircraft may have encountered wake turbulence from the two preceding helicopters in the formation.
- There was no evidence of pre-existing mechanical failure or engine malfunction prior to the impact.