What happened
On July 26, 2014, at 12:23 UTC, a Z 526 F aircraft, registration OK-CRA, was performing a glider tow operation at Chomutov Airport (LKCH). After successfully releasing the glider at approximately 900 meters above ground level, the pilot initiated a descent into the left circuit for runway 14.
During the approach, the pilot reported that the landing gear indicators showed green, signifying the gear was down. However, upon touchdown on runway 14, the aircraft did not land on its main wheels as expected. Instead, the nose of the aircraft dropped, causing the propeller to strike the ground, which resulted in the deformation of both propeller blades. The aircraft continued to move along the runway on a partially retracted gear, causing significant damage to the fuselage structure. The pilot was uninjured.
The investigation
The ÚZPLN investigation examined the aircraft's mechanical state and the pilot's actions. Post-accident inspections of the aircraft revealed extensive deformation of the fuselage's lower longerons and the rear floor. The investigation found that the landing gear was likely in an intermediate position and had not been properly locked in the extended position.
While the pilot and a witness both observed the gear in the extended position during the approach, the landing gear control switch was found in the "retracted" position during the post-accident inspection by the police. The investigation also noted that the landing gear electric motor was drawing excessive current and was malfunctioning. The mechanical indicators on the wings showed the gear was only partially extended (6mm to 8mm above the surface).
Findings
- The landing gear was likely in an intermediate position and was not secured by the over-center lock on the folding strut.
- The pilot likely inadvertently switched the landing gear control lever to the retracted position during the flight sequence.
- The force generated by the landing load was transmitted through the transmission shaft to the electric strut, causing it to buckle upward and damage the fuselage structure.
- The propeller strike and subsequent engine stoppage were caused by the nose of the aircraft dropping due to the collapsing gear.