What happened
On June 15, 2022, a HU 369D helicopter was performing agricultural spraying operations over a vineyard near Ellenz-Poltersdorf. The mission involved a series of short flights, each lasting approximately 12 minutes, with a ground crew providing fuel and pesticide refills between sorties.
After several completed flights, a second pilot joined the crew. At the time of the incident, the pilot noted a remaining fuel quantity of approximately 80 lbs. While preparing for an additional short spraying run, the 'FUEL LOW' warning light began to flicker. The pilot intended to complete the current pass and return to the refueling vehicle, but the warning light soon became steady. Shortly thereafter, at approximately 07:25 local time, the engine failed due to fuel starvation.
The pilot attempted an immediate controlled emergency landing. During the maneuver, the helicopter struck a stone wall on a slope, causing the aircraft to tip onto its side. The aircraft sustained heavy damage, including bent rotor blades and a damaged tail boom. Both pilots were able to exit the aircraft independently and sustained no injuries.
The investigation
The BFU investigation focused on the fuel management practices and the sequence of events leading to the engine failure. Investigators examined the aircraft's fuel system, noting that the fuel filter was empty upon inspection. The investigation also reviewed the operator's standard operating procedures (SOPs), which required a 10-minute fuel reserve for such operations.
Evidence showed that while the pilot maintained a log of flight times and fuel levels, the fuel gauges on this aircraft type were difficult to read accurately due to coarse scaling. The investigation also noted that the 'FUEL LOW' light is designed to illuminate permanently when fuel levels drop below approximately 37 lbs, but the engine failure occurred before the aircraft could reach the refueling point.
Findings
- The primary cause of the engine failure was fuel starvation.
- The pilot was attempting to complete a spraying pass after the fuel warning light had already activated.
- The fuel gauges on the HU 369D lacked the precision necessary for highly accurate real-time monitoring during low-fuel states.
- The aircraft's fuel quantity had depleted to a level where the engine could no longer maintain operation.