What happened
On the evening of 5 September 2014, a Robinson R-44 helicopter crashed in Roeselare, Belgium. The flight, which began at Kortrijk-Wevelgem airfield, was a cross-country trip intended to view a local car racing event. After visiting the exposition hall, the crew took off from an open field near the hall at approximately 18:00 UTC.
While flying over the exposition hall building, witnesses observed a sudden drop in engine and rotor sound frequency. The aircraft subsequently lost altitude and fell vertically into a parking lot, where the impact triggered a fire. Both occupants of the aircraft were killed in the accident.
The investigation
Investigators from the AAIU(Be) examined the wreckage and analyzed radar data, which showed the aircraft was at an altitude of approximately 130 meters (about 425 feet) before the crash. The investigation focused on the engine's performance and the cockpit controls.
Technical analysis of the wreckage revealed no evidence of mechanical failure prior to the impact. However, the mixture control knob was found in the idle cut-off position. The investigation also noted that the aircraft was flying at a low altitude and low airspeed, placing it within a dangerous flight envelope where emergency autorotation is difficult. Furthermore, the investigators found that the plastic guard intended to prevent accidental movement of the mixture control was not in place.
Findings
- The primary cause of the accident was an engine stoppage occurring at a low altitude and low airspeed.
- This stoppage was triggered when a crew member accidentally pulled the mixture control knob to the cut-off position while attempting to adjust the carburetor heat control.
- The post-impact fire was caused by the rupture of the fuel tanks, allowing fuel to leak onto hot engine components.
- Contributing factors included time pressure to land before sunset and the aircraft's failure to maintain the minimum required altitude when flying over a crowded area.
Safety action
- The investigation identified a safety issue regarding the vulnerability of the mixture control to human error and recommended that the Robinson Helicopter Company improve the guard system on the Robinson R-44.
- A safety concern was raised regarding the lack of fuel bladder tanks, leading to a recommendation that the FAA require compliance with service bulletins for fuel tank retrofits to improve resistance to leaks during accidents.