What happened
On July 13, 2016, a Maule MX 7-235, registration OK-LSV, was performing a glider tow at Zbraslavice Airport (LKZB) as part of a gliding competition. After completing the tow at an altitude of 600 m AGL, the pilot began a descent. The landing on runway 33 was described as smooth, touching down near the three-point position with the engine at idle.
During the landing roll, the pilot heard a loud snap, followed by the immediate collapse of the left main landing gear strut. This caused the aircraft to tilt to the left, resulting in the left wing making contact with the ground. The aircraft then pivoted approximately 170 degrees before coming to a stop. There were no injuries to the pilot, though the aircraft sustained significant damage, including a broken propeller, damaged wing covering, and a cracked windshield.
The investigation
An investigation by the ÚZPLN focused on the mechanical failure of the landing gear and the pilot's condition. Technical analysis of the failed left main landing gear strut was conducted by the Aviation Research and Test Institute (VZLÚ). The examination focused on the area where the steel tube had been reinforced with welded external plates and internal steel rings.
Microscopic analysis of the fracture surfaces revealed a combination of fatigue and static ductile failure. The investigation established that multiple fatigue cracks had initiated at the area of the weld, specifically near a hole in the tube where the microstructure had been altered by the welding process.
Findings
- The primary cause of the accident was a fatigue failure of the left main landing gear strut piston.
- The failure originated due to the initiation of fatigue cracks in the area of the tube's reinforcement, caused by changes in the material's microstructure following the welding of the internal ring and external plates.
- The pilot was operating the aircraft under the influence of residual alcohol. While the pilot was in the elimination phase of alcohol metabolism and the level was considered low impairment by general standards, it was found to be negatively affecting the pilot's performance from an aviation medical perspective.
- The landing technique and weather conditions were appropriate and did not contribute to the structural failure of the aircraft.