What happened
On the evening of March 16, 2012, an Agusta Bell AB 47 G2 helicopter, registration F-GBEG, was performing agricultural spraying operations in Basse Pointe, Martinique. After refueling with 40 liters of unleaded automotive gasoline and 100 liters of phytosanitary product, the pilot began treating the final plots of a banana plantation. Upon reaching the edge of the second plot, the engine power significantly decreased. The aircraft struck the banana trees and the ground before catching fire. The pilot was able to unbuckle the harness and evacuate the aircraft safely before the fire spread.
The investigation
The investigation focused on the mechanical state of the engine and the quality of the fuel used. Examination of the wreckage and the impact site revealed that the aircraft struck the vegetation at a low speed and with low intensity. Technical analysis of the rotating components showed that the engine and radiator fan were not rotating at the moment of impact, indicating a loss of power prior to the collision.
Investigators found that the carburetor contained partial obstructions in the conduits and the jet. Analysis of fuel samples from both the wreckage and the operator's supply tank revealed the presence of mineral sediments. Furthermore, the fuel used was unleaded automotive gasoline, which was stored in a translucent 1000-liter plastic agricultural tank that was not buried and was exposed to significant temperature fluctuations due to inadequate protection from sunlight.
Findings
Several factors contributed to the engine failure:
- The use of unleaded automotive gasoline, which is not authorized by the engine manufacturer (Lycoming) or the carburetor manufacturer (Precision Airmotive) for this engine type.
- The occurrence of vapor lock, a phenomenon facilitated by the use of automotive gasoline, which has a higher vapor pressure than the required AVGAS 100 LL.
- The presence of sediments and gums within the fuel, which caused partial blockages in the carburetor.
- Inadequate fuel storage conditions, where the use of a non-specialized, translucent plastic tank led to fuel degradation and increased gum content due to temperature swings.
Safety action
Following a series of similar accidents involving the same operator, several preventive measures were implemented by the regulatory authority:
- Mandatory inspection of engines and carburetors for the operator's fleet in accordance with manufacturer service bulletins.
- A strict requirement to use only AVGAS 100 LL.
- A reduction in the maximum takeoff weight by 50 kg for pilots with fewer than 500 hours of spraying experience.
- Mandatory use of helmets and safety harnesses.
- The replacement of oily adjuvants (such as "Banol") with water for spraying to improve pilot visibility by reducing windshield contamination.