What happened
On July 2, 2015, a pilot was conducting flight operations at the Konstancin airfield following recent maintenance and test flights. After completing an initial flight, the pilot closed the main valve of the aircraft's pneumatic system. When preparing for a second flight, the pilot failed to reopen this valve before engine start-up.
Although the engine started using residual compressed air, the pilot discovered that the landing gear could not be retracted after takeoff. The cockpit indicators continued to show the gear as extended, and mechanical indicators confirmed this status. The pilot limited the flight to the airfield pattern and landed on runway 30 at approximately 10:10 LMT.
During the landing roll, the right main landing gear strut began to collapse. This caused damage to the lower fuselage skin and caused the aircraft to veer to the right. The aircraft subsequently struck high crops of rapeseed on the side of the runway, which deepened the turn and caused the aircraft to undergo a 180-degree excursion. The incident resulted in significant damage to the left wing, left flaps, elevator, and rudder, though the pilot escaped the cabin without injury.
The investigation
The PKBWL investigation examined the aircraft's maintenance history, the pilot's credentials, and the mechanical operation of the pneumatic system. The investigation established that the aircraft, a TS-8 Bies with registration SP-YBD, had been meticulously maintained as a museum exhibit.
Investigators analyzed the landing gear mechanism and found that the locks holding the gear in the extended position had actually disengaged during the attempt to retract the gear. However, because the pneumatic system lacked sufficient pressure to complete the retraction, the microswitches and mechanical indicators did not update to reflect the unlocked state. Consequently, the pilot believed the gear was still securely locked in the down position and did not attempt emergency extension procedures.
Findings
- The primary cause of the accident was a pilot error involving the failure to follow standard engine start-up procedures regarding the pneumatic system valve.
- Insufficient air pressure in the main pneumatic system prevented the completion of the landing gear retraction sequence.
- The aircraft's design allowed the gear locks to disengage without triggering the cockpit warning lights or mechanical indicators, leading to a false sense of security for the pilot.
- The aircraft sustained significant damage to the fuselage, left wing, flaps, and control surfaces due to the gear collapse and subsequent contact with vegetation.