What happened
On June 13, 2013, a Hughes Helicopters, Inc. HU 369D was performing agricultural spraying operations in the vicinity of Bernkastel-Wehlen, Germany. A refueling and spraying station had been established in a nearby vineyard to support the mission. Following 17 successful flights, the pilot took a passenger on board for a final flight of the day to clarify boundary markings for the spraying areas.
During the flight, which was conducted at a very low altitude of approximately 10 meters, the pilot noted that the "Fuel Low" warning light had illuminated. While the passenger reported the light remained on continuously, the pilot stated it had flickered two to three times, which he did not consider an immediate emergency as he believed approximately 10 minutes of flight time remained. As the helicopter transitioned through the vineyard, the "Engine Out" warning light activated accompanied by an audible alarm. The aircraft lost power, began to rotate to the right, and struck the terrain. The helicopter tumbled down a steep slope, eventually coming to rest on its side.
The investigation
The BFU examined the wreckage and the circumstances leading to the loss of power. Investigators found that the helicopter was equipped with an ISOLAIR-3700 spraying system and had undergone its 100-hour inspection shortly before the accident. The investigation included an analysis of the fuel system, noting that a new fuel sender had been installed during a previous 300-hour inspection, which triggers the "Fuel Low" warning when less than 27 liters remain.
Upon inspecting the aircraft, investigators found little to no residual fuel in the fuel lines, filters, or the damaged fuel tank. There was no evidence of mechanical failure in the flight controls or an engine fire. The investigation also reviewed meteorological data from Frankfurt-Hahn airport, which indicated favorable flying conditions at the time of the accident.
Findings
- The primary cause of the accident was fuel starvation.
- The pilot continued flight operations after the "Fuel Low" warning light had illuminated, despite the flight manual instruction to land as soon as possible.
- The aircraft was heavily damaged, and the tail boom was severed during the impact.
- The pilot sustained serious injuries, while the passenger escaped with minor injuries.