What happened
On July 6, 1998, during a group flight demonstration over Vilnius celebrating Statehood Day, a JAK-52 aircraft, registration LY-BJK, experienced a landing gear malfunction. After completing the demonstration flight, the crew returned to Kyviškės Aerodrome. Upon attempting to extend the landing gear, the pilot observed that the left main gear remained in the retracted position, indicated by a red warning light and mechanical indicator.
The pilot attempted several procedures to resolve the issue, including cycling the gear and performing various aerobatic maneuvers to use centrifugal force to dislodge the gear from its locking hook. When these efforts failed and fuel reserves became a concern, the pilot elected to retract the right landing gear and perform an emergency belly landing on the grass runway. The aircraft landed at 13:40 local time without further incident.
The investigation
The investigation focused on why the left landing gear failed to extend. While the aircraft sustained minor damage—including broken propeller blade tips and deformed landing gear covers—the pilot was uninjured.
Technical examination of the pneumatic system revealed that the air cylinder responsible for releasing the locking hook in the retracted position had failed. Specifically, investigators found that the orifice through which compressed air is supplied to the cylinder was completely blocked. Laboratory analysis of the debris found within the air line identified various contaminants, including soil minerals, paint flakes, and organic matter (a birch seed). These foreign particles had obstructed the narrow 4mm diameter passage.
Findings
- The primary cause of the accident was an emergency belly landing necessitated by the failure of the left landing gear to extend.
- The failure was caused by contamination within the pneumatic system, specifically mechanical debris blocking the air supply orifice to the landing gear release cylinder.