What happened
On June 16, 2018, during an airshow at Muchowiec Airport in Katowice, a UL aircraft, registration EP-1Tulak, departed for a flight toward Wrocław. Due to the ongoing airshow activities, the pilot opted to take off from a point other than the end of the runway.
Immediately following takeoff, the pilot experienced intense vibrations in the horizontal stabilizer. Fearing that the vibrations could lead to the structural destruction of the aircraft's tail section, the pilot determined that the remaining runway length was insufficient for a straight-ahead landing. After notifying the flight manager of the situation and the intention to turn, the pilot executed a 180-degree left turn to land with the wind. The aircraft subsequently performed an emergency landing on a grassy area of the airfield.
The investigation
The PKBWL examined the aircraft following the incident. Post-flight inspections revealed that the internal part of the trim tab flap, which holds the trim drive wires, had broken off. A pre-flight inspection by the pilot had not identified any prior damage to the trim system.
Investigators noted that the aircraft was parked with its tail facing aerobatic aircraft participating in the airshow. It was determined that the propeller slipstream from another aircraft's engine start could have contributed to the damage. The inspection also revealed significant operational wear on the aircraft. The damage to the plywood trim tab flap was characterized by the delamination of the second and fourth wood layers, and significant play was found in the hinges attaching the trim tab to the elevator.
Findings
- The primary cause of the incident was the mechanical failure of the trim tab.
- The failure was facilitated by the aging of the wood, exacerbated by exposure to environmental factors.
- The physical nature of the damage suggests a mechanical force caused the breakage.
- The positioning of the aircraft, facing the slipstream of other active aircraft, was a contributing factor.