What happened
On February 6, 2015, at 10:55 UTC, a B&F FK-14B Polaris, registration CS-URO, was performing a leisure flight at the Alqueidão Azambuja airfield in Portugal. Shortly after takeoff, the aircraft entered a stall and subsequent spin. Due to the low altitude at which the stall occurred, the pilot had no opportunity to recover the aircraft. The plane struck the ground with significant vertical speed, causing the airframe to disintegrable upon impact. The collision resulted in two fatalities and the total destruction of the aircraft. A post-impact fire also occurred, destroying all onboard documentation.
The investigation
The GPIAA investigation focused on the aircraft's performance parameters and flight conditions. Investigators examined the aircraft's mass and balance, noting that the engine was producing power at the moment of impact and no pre-existing technical failures were reported. The investigation also reviewed the pilot's qualifications and the aircraft's documentation, finding that while the pilot was properly qualified, the aircraft's flight certificate had expired. The investigation also analyzed the impact dynamics, determining that the high inertial forces during the rapid deceleration caused the structural breakup and made survival impossible for the occupants.
Findings
Several critical factors contributed to the accident:
- The aircraft took off with a mass exceeding the authorized maximum take-off mass.
- The flight was conducted with a rear center of gravity.
- The takeoff was performed with a 10-knot tailwind.
- The aircraft lacked a stall warning system.
- The stall and subsequent spin occurred at an altitude too low for recovery maneuvers.
Safety action
The GPIAA issued safety recommendations to the Portuguese Civil Aviation Authority (ANAC) to launch an awareness campaign regarding the dangers of exceeding maximum take-off mass and improper weight and balance. Additionally, the GPIAA recommended that the Portuguese Ultralight Aviation Association (APAU) advise pilots to perform high-drag maneuvers only at safe altitudes, verify actual empty weight rather than relying on standard figures, and strictly adhere to mass and balance calculations.