What happened
On May 24, 1969, a Cessna 150 (registration HB-CSD) was conducting a training flight at Wangen-Lachen airfield. The flight, part of a student pilot's training program managed by the Motorfluggruppe Zürich, involved a series of landing practice maneuvers.
During a landing attempt from 600 meters, the student pilot touched down on the main wheels approximately 70 meters from the start of the runway. The aircraft was positioned roughly 20 degrees left of the runway centerline with flaps fully extended. As the aircraft rolled, it drifted toward the left edge of the paved surface. In an attempt to correct the course, the pilot steered toward the right, causing the aircraft to cross the runway boundary by approximately one meter. Upon hitting the uneven ground at the edge of the pavement, the nose gear collapsed, bringing the aircraft to an immediate halt and stalling the engine.
The investigation
The investigation focused on the structural integrity of the nose gear assembly and the circumstances of the landing. Investigators examined the tubular construction of the nose gear strut and identified fracture patterns consistent with an overload.
Testing was also conducted using the same aircraft type to determine if the steering mechanism's integrity was compromised. These tests demonstrated that the aircraft remained steerable on the ground even if one of the nose gear steering bolts were missing, suggesting that a failure in the steering linkage was not the primary cause of the excursion.
Findings
- The primary cause of the accident was the failure of the nose gear strut due to structural overload.
- The combination of the uneven terrain at the runway edge and the pilot's steering correction applied significant stress to the nose gear assembly.
- While the aircraft was properly maintained and airworthy, investigators noted that the manufacturer's maintenance manual did not require periodic inspections for hardness or cracks in these specific landing gear components.
- It was noted that the nose gear assembly may have been subject to prior deformation from previous hard landings during training operations, though no such incidents had been officially reported to the maintenance department.