What happened
On 8 April 2017, an SZD-55-1 glider, registration G-CKLR, was involved in a fatal accident during a private towed launch at Currock Hill Airfield, Northumbria. Following recent maintenance work on the aircraft's avionics, the pilot prepared the glider for flight. During the takeoff roll, the tug aircraft experienced a sudden deceleration as the glider began to climb rapidly and adopt an extreme pitch angle. The tow rope released, and the glider reached an estimated height of 100 feet before rolling to the right and descending nose-first into the ground. The impact caused extensive damage to the aircraft, and the pilot sustained one fatal injury.
The investigation
The AAIB examination of the wreckage revealed that the elevator control connection had not been properly engaged during the rigging process. While the tailplane appeared correctly seated on the fin, the elevator lever was found to be sitting behind the mechanism rather than inside it. This mis-rigged state meant that while the pilot could move the control stick, the elevator could only move upwards under gravity or airflow, with no effective downward deflection available.
Investigators discovered that the slot in the tail fin's horizontal rib had been enlarged through an unapproved modification. This enlargement removed the original design's ability to prevent improper connection. Testing confirmed that with this larger slot, the elevator lever could easily slip into the void behind the mechanism if the control stick was in a forward position during assembly. The investigation also noted that the pilot had recently performed extensive work on the cockpit area, which involved significant disassembly of the aircraft.
Findings
- An unapproved and historic modification had enlarged the elevator lever slot, which compromised the aircraft's designed safety features.
- The enlarged slot created a latent condition where the elevator control could be mis-rigged without any visible indication.
- During the rigging process, the elevator lever failed to engage the mechanism, leaving the pilot with no effective pitch control during the launch.
- The pilot was unable to detect the error, as a full-and-free control check would have been required to identify the lack of downward elevator movement.
Safety action
- The European Aviation Safety Agency (EASA) has indicated its intention to issue an Airworthiness Directive to mandate inspections of the SZD-55-1 fleet to ensure tail fin slot dimensions meet design specifications.
- A Safety Recommendation was made to the British Gliding Association (BGA) to review its guidance regarding the necessity of positive control checks on gliders designed with automatically-connecting controls.