What happened
On November 22, 2007, a Hughes 369D helicopter was performing a specialized mission to apply lime to forest areas near Kaiserslautern, Germany. The aircraft was operating on behalf of the local forestry administration. After completing an initial flight and returning to refuel, the pilot departed again at approximately 10:00 AM.
During the return flight to replenish the lime spreader, while flying at an altitude of between 30 and 50 meters, the engine experienced a sudden loss of power and RPM. An "engine out" indication appeared on the instrument panel. The pilot attempted an emergency autorotation, landing the helicopter in a field. During the impact, the aircraft's tail boom broke off, and the front right skid collapsed. The aircraft sustained heavy damage, and while there were no injuries to the pilot, the incident caused damage to the field.
The investigation
The BFU examined the aircraft and the fuel system to determine the cause of the power loss. Investigators checked the fuel level at the time of the accident; the pilot reported approximately 50 liters of fuel remaining in the tank. Upon inspection of the fuel gauge and tank sensor, investigators found that the float mechanism was functioning correctly and moving in sync with the gauge. However, they discovered a broken wire in the supply line to the low-fuel warning lamp, which prevented the warning light from illuminating when fuel levels were low.
Further examination of the rubber fuel tank showed no signs of damage, and the fuel filler neck remained intact following its inspection by local police.
Findings
- The primary cause of the accident was a sudden engine power loss during flight.
- A broken wire in the wiring harness prevented the low-fuel warning light from activating, although the fuel level was not yet critically low at the time of the failure.
- The impact of the forced landing caused the separation of the tail boom and structural failure of the landing skids.