Incident Description
On 22 May 2021, a glider training flight was conducted at the Radawiec Duży airfield (EPLE) using a winch launch. After launch, the crew – consisting of a student and an instructor – experienced a lack of response from the glider when the control stick was pushed forward (elevator down command). The instructor took over control, released the tow at approximately 300 meters altitude, performed a circuit, and landed using the elevator trim tab. The crew sustained no injuries, and the glider was not damaged.
Investigation Findings
A post-flight inspection of the glider's elevator control cable system revealed a disconnection of a turnbuckle from the cable at the upper part of the cable drive lever. Additionally, two turnbuckles between the cable drive lever and the final drive lever were found uncottered – the very location where the disconnection occurred. The assembly of all control cable connections in the glider was checked, and the detected fault was rectified. Subsequently, the control systems of all other gliders operated by the same user were inspected, and no anomalies were found.
Cause and Contributing Factors
The probable cause of the incident was an undetected assembly error by the maintenance organization in the elevator control system, committed during the replacement of cables in that system. A contributing factor was that the task of verifying the correct assembly of cables was not classified as a critical task in the documentation of the organization that performed the cable replacement.
Preventive Actions
The following preventive actions were implemented by the investigating entity: 1. Verification of the correct assembly of the control system on the glider involved in the incident. 2. Inspection of the control systems on all other gliders operated by the user. 3. Supplementation of the glider user's task cards for control system maintenance to indicate critical tasks. 4. Supplementation of the task cards of the organization that performed the cable replacement to indicate critical tasks.
No additional safety recommendations were issued by the commission.