What happened
On April 8, 2006, a Sportavia RF 5B touring motor glider, registration PH-626, was being prepared for flight at the Aeroclub Valkenburg. The aircraft features a folding wing design to save space in hangars. Prior to the flight, club members were in the process of unfolding and securing the outer wing sections. The pilot and passenger arrived while this process was still being finalized and proceeded with the flight without personally performing the wing locking procedures.
During the takeoff roll on runway 23, the aircraft encountered a 16-knot wind from 250 degrees. To maintain the centerline against this crosswind, the pilot applied aileron input. As the aircraft reached rotation speed and the ailerons were returned to a neutral position, the outer section of the right wing unexpectedly pivoted upward around its hinge, reaching an angle of approximately 90 degrees. This sudden loss of lift on the right side caused the aircraft to roll violently to the right. The aircraft struck the ground near the runway, flipped onto its back, and immediately caught fire. Both occupants of the Sportavia RF 5B sustained fatal injuries.
The investigation
The investigation focused on the integrity of the wing locking mechanism. While the locking pin was found in the extended position and the control lever appeared correctly set, the inspection of the wing's attachment points revealed that the outer wing section had not been properly secured. The investigation established that the locking lever can be moved to the correct position even if the wing is not fully engaged, provided the wing is not visibly misaligned.
Investigators also examined the pre-flight inspection process. It was noted that the pilot did not participate in the wing assembly and there was no evidence that a thorough check of the locking mechanism was performed. Furthermore, the aircraft's flight manual specifies that the locking and securing must be checked, but does not provide specific instructions on how to verify the integrity of the connection.
Findings
- The primary cause of the accident was that the aircraft took off with an improperly secured right wing.
- The use of aileron input to counteract a crosswind during the takeoff roll initially held the unsecured wing in place, but returning the controls to neutral allowed the wing to rotate upward.
- The pilot did not personally verify the wing's locking status during the pre-flight inspection, as the assembly was being handled by others.
- The locking mechanism allows the control lever to appear in the correct position even when the wing is not properly seated.