What happened
On April 8, 1997, at approximately 11:40 local time, a Piper PA-28-161 Warrior, registration HB-PEY, was conducting local landing training at Lausanne Airport. The flight, operated for instructional purposes, involved an instructor and a student pilot. During the fifth touch-and-go maneuver of the session, the upper attachment of the left landing gear strut failed during the takeoff roll.
Following the structural failure, the aircraft touched down on runway 01. The left landing gear leg remained attached only by the brake line. After traveling approximately 120 meters along the paved surface, the aircraft veered 90 degrees to the left and came to a stop in the grass. The crew members were unharmed, though the aircraft sustained damage to the left landing gear and left flap.
The investigation
Investigators examined the aircraft's maintenance history and the physical remains of the landing gear assembly. The Piper PA-28-161 Warrior had recorded 5,826 total flight hours and 13,850 landings. Maintenance records indicated that the aircraft was in compliance with required service intervals, with the most recent 100-hour inspection completed shortly before the accident.
Technical analysis focused on the upper linkage of the pantograph, which was constructed of lightweight cast metal. The fracture was sent to the Federal Materials Science and Technology Laboratory (EMPA) for metallographic examination. The laboratory analysis of the fracture surface confirmed that the failure was a fatigue fracture resulting from relatively low nominal stress.
Findings
- The primary cause of the accident was a fatigue fracture of the left landing gear strut.
- The aircraft had a high number of landings (13,850), many of which were performed during instructional flights on uneven runway surfaces, contributing to the fatigue of the metal component.
- The existing maintenance program did not include specific inspections for cracks within the landing gear assembly.
- Meteorological conditions at the time of the accident were clear with good visibility and light winds, and did not contribute to the event.