What happened
On August 30, 2012, an Agusta Bell AB 47 G2, registered F-GHYS, was performing aerial spraying operations near L’Ajoupa-Bouillon. While flying over a banana plantation, the pilot attempted to clear a treeline, at which point they experienced a decrease in main rotor RPM followed by a loss of engine power. The pilot performed an emergency landing straight ahead into the middle of the plantation. The aircraft sustained damage during the impact.
The investigation
The investigation focused on the mechanical state of the engine and the fuel used during the flight. While the wreckage and engine examination revealed no specific mechanical anomalies, investigators looked into the operator's recent history. The operator had experienced five accidents involving the same aircraft type on Martinique between March and September 2012. Technical examinations of four of those previous incidents revealed that the fuel being used was unleaded automotive gasoline.
Investigators noted that the use of unleaded automotive gasoline is not authorized by the engine manufacturer, Lycardi (VO-4356AID), or the carburetor manufacturer, Precision Airmotive. Furthermore, the investigation established that using unleaded gasoline with a higher vapor pressure than standard AVGAS 100 LL increases the risk of vapor lock.
Findings
- The use of unsuitable fuel likely caused the engine power loss through a vapor lock phenomenon.
- The pilot's decision to perform an immediate emergency landing directly ahead likely mitigated the severity of the accident.
- The pilot had previously experienced a similar engine failure and forced landing under similar circumstances five months prior.