What happened
On October 10, 2020, a ZLÍN Z 526 AFS-V, registration OK-CXC, was performing a glider tow operation at Olomouc Airport (LKOL). During the fourth takeoff of the day, while the aircraft was accelerating on the grass runway 27R, the main landing gear retracted. The aircraft reached a speed of approximately 80 km/h IAS when the gear moved into the up position, causing the aircraft to lose support and belly-land on the runway.
The impact caused the propeller to strike the ground, resulting in the destruction of the propeller blades and a violent engine stoppage. The aircraft slid approximately 50 meters along the unpaved surface before coming to a halt. The pilot of the towing aircraft was uninjured. The glider being towed, an L-23 Super Blaník, was operated by an instructor and a student; the instructor successfully disconnected the towline and performed an emergency landing on a parallel runway without further incident.
The investigation
The ÚZPLN investigation examined the aircraft's maintenance history, the pilot's experience, and the mechanical state of the landing gear system. The investigation found that the aircraft had a valid airworthiness certificate and that all mechanical components, including the electric landing gear motor and the retraction mechanism, were fully functional prior to the accident. No technical failures were identified in the aircraft's systems.
Investigators also reviewed the pilot's pre-flight actions. The pilot, an experienced aviator with significant hours on the Z 526 type, had performed several successful tow operations earlier that day. The investigation focused on the sequence of events during the takeoff roll and the physical damage sustained by the airframe and engine components.
Findings
- The primary cause of the accident was the incorrect movement of the landing gear switch to the 'up' position during the takeoff roll.
- The pilot likely performed this action while conducting pre-flight checks, potentially confusing the gear switch with other cockpit switches that are standardly moved to the 'up' position during startup.
- The retraction of the gear occurred after the aircraft had lightened the load on the wheels but before sufficient airspeed had been reached for takeoff.
- The landing gear mechanism suffered structural deformation due to the extreme dynamic loads applied when the gear retracted while the aircraft was still under significant weight and moving forward.
- The damage to the engine, including torn engine mounts and propeller destruction, was a direct result of the propeller striking the ground during the belly landing.