What happened
On June 30, 2007, a B&F FK14B Polaris, registration OO-F37, departed Kiewit airfield for a local flight. The aircraft was carrying two pilots. Shortly after reaching an altitude of approximately 1500 feet, the pilot in command executed a steep 60-degree climb, followed by a brief level flight. The aircraft then entered a sharp right bank, which transitioned into a high-speed spin.
During the descent, the engine flamed out after the power was reduced. Although the aircraft managed to recover from the spin at an altitude of roughly 50 meters, it had lost nearly all forward momentum. The aircraft subsequently impacted a residential backyard at 3 Wanbeekstraat in Hasselt in a nose-down position. While the first pilot managed to escape the wreckage before a fire broke out, the second pilot passed away from a heart attack prior to the fire. The aircraft was destroyed by the impact and subsequent flames.
The investigation
The investigation examined the aircraft's weight, engine performance, and the physical condition of the crew. Investigators found that the aircraft was operating significantly above its Belgian certified maximum takeoff weight (MTOW) of 450kg, with an estimated excess of over 30kg due to the weight of the two occupants and a large fuel load.
Regarding the engine, the investigation determined that the Rotax 912S engine flamed out because the carburetor design is susceptible to fuel ejection during negative acceleration or nose-down attitudes. The investigation also noted that the aircraft's manual explicitly prohibits acrobatic maneuvers, including spins and bank angles exceeding 60 degrees.
Findings
- The primary cause of the accident was a hard right banking maneuver that induced a high-speed spin from which the pilot could not recover.
- A contributing factor was the engine flame-out during the spin.
- The aircraft was operating in excess of its certified MTOW.
- The second pilot suffered a fatal heart attack, which investigators noted may have potentially caused uncontrolled aircraft movements, though this could not be scientifically proven.
Safety action
While no direct safety recommendations were issued for the accident itself, the investigation highlighted a lack of adherence to weight limits among some ultralight pilots. It was suggested that the Belgian Civil Aviation Authority (BCAA) consider an awareness campaign to emphasize the technical and safety importance of respecting the 450kg MTOW limit.