What happened
On May 22, 2021, an SZD-9 bis 1E Bocian glider, registration SP-3774, was performing winch-launched training flights at the Radawiec Duży aerodrome (EPLR). Following takeoff, the crew, consisting of a student and an instructor, discovered that the aircraft failed to respond to aft stick inputs, indicating a lack of elevator downward deflection.
The instructor took control of the aircraft. After releasing from the winch at an altitude of approximately 300 meters, the instructor performed a circuit and landed the glider using the elevator trim tab to maintain control. There were no injuries to the crew and no damage to the aircraft.
The investigation
Upon inspection of the aircraft, investigators identified that a puller had become disconnected from the cable in the upper section of the cable drive lever. Furthermore, two pullers (upper and lower) located between the cable drive lever and the end drive lever were found to be unfastened, which was the specific location where the disconnection occurred.
Following the incident, the user'/operator's fleet was inspected. All control cable connections in the remaining gliders were checked, and no further irregularities were found. The identified fault in the subject aircraft was subsequently repaired.
Findings
- The primary cause of the incident was an undetected assembly error in the elevator control system, which occurred during the replacement of control cables.
- A contributing factor was that the maintenance organization's documentation failed to classify the verification of cable assembly as a critical task.