What happened
On 4 May 2018, an AS341-F2 Gazelle helicopter, registration ZU-RLE, departed from Honeymoon Game Farm in the Limpopo Province, bound for Makoppa. Shortly after the aircraft became airborne, the engine ceased operation, forcing the pilot to execute an emergency landing in nearby savannah bushland. During the landing maneuver, the pilot applied maximum collective pitch and aft cyclic control to cushion the impact with trees, which caused the main rotor blades to strike and sever the tail boom. Despite the significant structural damage, there were no injuries to the pilot or the passenger.
The investigation
Investigators examined the aircraft's fuel system and the refueling source used prior to the flight. The helicopter had been refueled from a private fuel trailer located on the farm. Upon inspection of the aircraft's fuel control unit (FCU) filter, investigators found significant amounts of water contamination. Furthermore, a sample taken from the fuel trailer revealed brownish fuel containing sediment and dirt.
Analysis determined that the engine initially operated normally because the aircraft's feeder tank likely contained clean residual fuel from a previous flight. The engine failure occurred only after the clean fuel in the feeder tank was exhausted and contaminated fuel from the main tank reached the engine. The investigation also noted that the pilot's pre-flight inspection, which involved draining fuel from a purge valve, only checked the feeder tank and did not reveal the contamination present in the main tank.
Findings
- The primary cause of the engine stoppage was fuel contamination involving water and sediment.
- The pilot refueled from a private trailer without verifying the fuel quality, relying instead on the presence of a 1-micron filter.
- The fuel trailer's refill cap lacked a locking mechanism, leaving the fuel vulnerable to potential tampering or the introduction of water.
- The aircraft's fuel drain/purge valve design allowed the pilot to inspect the feeder tank without detecting the contaminated fuel held in the main tank.