What happened
On March 14, 2009, a KW1 glider, registration PT-PFO, was performing a local flight at the Balsa Nova airfield in Paraná, Brazil. The flight began with a standard aero-tow procedure. During the takeoff roll, observers on the ground noted that the aircraft's aerodynamic brake (spoiler) had inadvertently deployed.
At an altitude of approximately 400 meters, after disconnecting from the tow cable, the pilot received a visual signal from the tow plane. The tow plane pilot used rudder oscillations to communicate that the glider's spoiler was open. However, the glider pilot misinterpreted this signal as an indication of engine failure in the tow aircraft. Consequently, the pilot initiated a return to land without rectifying the spoiler position. During the low-altitude landing attempt, the aircraft entered a left-hand turn and struck the ground, resulting in substantial damage to the aircraft and serious injuries to the pilot.
The investigation
The CENIPA investigation focused on why the spoiler deployed and why the pilot failed to respond to the tow plane's warning. Investigators examined the aircraft's spoiler mechanism and found that the system lacks a specific indicator for an unlocked state, showing only "open" or "closed."
Testing on similar aircraft revealed that the spoiler could be accidentally unlocked by applying force to the control lever. In the accident aircraft, the spoiler guard was approximately 15 cm smaller than that of a comparable model, leaving the control rod more vulnerable to accidental contact. Investigators concluded that the pilot's left arm or parachute may have struck the rod during takeoff. Furthermore, the investigation noted that the pilot had been away from regular flying activities for some time, averaging fewer than two flights per month, which likely contributed to the misinterpretation of the visual communication.