What happened
On September 24, 2006, a K 7 Rhönadler glider, registration PH-351, departed from runway 24 at De Peel Airbase for a local flight. During the rotation phase of the winch launch, the pilot found that the control stick could not be pulled backward. This obstruction was caused by a rubbery object lodged in the center position of the stick.
As the launch progressed, the aircraft failed to achieve the expected steep climb, maintaining a flat trajectory instead. The pilot reported that the airspeed increased uncontrollably to 130 km/h. To signal the danger of excessive speed, the pilot performed yawing maneuvers to alert the winch operator. Despite these signals, the winch operator initially reduced power only slightly, continuing the launch until the pilot eventually released the cable at an altitude of approximately 150 meters.
Immediately after disconnecting from the cable, the glider experienced a right-hand roll. The pilot managed to move the control stick slightly to the right, executing a wide 225-degree turn. After reaching an altitude of about 100 meters, the control stick regained full range of motion, allowing the pilot to reduce speed and complete a landing on the left side of the winch area. There were no injuries and no damage to the aircraft.
The investigation
The investigation focused on the cockpit configuration following a recent maintenance check. Prior to the day's flights, a technician had performed a C-inspection on the PH-351. During this inspection, the technician noted that the battery wiring was not properly positioned and was curling beneath the instrument panel. To address this, the technician wrapped the dual-core cable in a less flexible sleeve and secured it between air hoses under the instrument panel.
Post-flight analysis revealed that the battery cable had excessive slack and had experienced tension at the battery plug. The investigation established that the cable was capable of forming a loop around the upper part of the control stick. It is believed that during the initial phase of the launch, this loop shifted onto the stick, preventing the pilot from pulling it backward.
Findings
- The primary cause of the control difficulty was a loop of battery wiring that moved into the path of the control stick during the launch.
- The technician failed to properly secure the wiring during the C-inspection, opting to use a sleeve and clamps rather than ensuring the original, correct positioning of the cable.
- The pilot's pre-flight cockpit check failed to detect that the cable had enough slack to interfere with the control stick movement.