What happened
On June 13, 2017, a Diamond DA 20-A1, registration OK-BLB, was performing a local flight from Hosín airport (LKHS). During the takeoff roll, the bolt securing the nose gear fork assembly failed. As the aircraft lifted off, the nose gear fork and wheel detached from the aircraft. The pilot, unaware of the missing component, continued the flight and performed a standard landing on runway 24R.
During the landing rollout, the pilot heard an unusual metallic grinding sound. Upon realizing that the remaining portion of the nose gear strut was dragging on the asphalt, the pilot increased the angle of attack and steered the aircraft toward the grass verge to avoid further damage or fire risk. However, as the aircraft slowed, the nose gear strut dug into the soft turf, causing the aircraft to nose over. This resulted in the rotating propeller striking the ground, causing damage to both propeller blades and the nose gear assembly. There were no injuries to the pilot.
The investigation
The ÚZPLN examined the wreckage and the failed hardware. The investigation focused on the broken bolt that secured the nose gear fork assembly. Microscopic analysis of the fracture surface revealed characteristics of slow-developing fatigue failure. While corrosion products and secondary contamination prevented a definitive determination of the initial crack origin, the analysis confirmed that multiple fatigue cracks had initiated around the circumference of the bolt threads.
Findings
- The primary cause of the accident was the failure of the bolt securing the nose gear fork assembly due to fatigue.
- The pilot was unaware that the gear assembly had detached during the takeoff phase.
- The pilot's decision to steer onto the grass was an attempt to mitigate damage, but the soft surface caused the gear to dig in, leading to the propeller strike.
- The aircraft was fully airworthy and the pilot held a valid CPL(A) license.