What happened
On September 1, 2023, a Tecnam P2002 JF, registration SP-ADW, was conducting a PPL(A) training flight when a significant mechanical failure occurred during the landing roll. After touching down on runway 26 and traveling approximately 30 meters before braking, the crew observed the aircraft's cowling dropping. This movement caused the propeller blades to strike the ground, resulting in propeller damage and subsequent engine shutdown. The crew, consisting of an instructor and a student pilot, sustained no injuries.
Post-incident inspection revealed that the front landing gear strut and fork had shifted rearward because the shock absorber mount had broken. The failure caused the front wheel fork and shock absorber to collapse under the fuselage, damaging the wheel rim and breaking the upper shock absorber mount. Significant irregularities were also noted on the grass runway surface.
The investigation
The investigation focused on the structural failure of the landing gear components. Investigators recovered a portion of the broken lower shock absorber mount pin 15 meters behind the aircraft. Examination of the pin revealed that the fracture occurred on the threaded section along the inner wall of the left fork.
Technical analysis showed that the threads on the failed pin were heavily crushed compared to a new component. This degradation created increasing clearance within the fork, leading to movement under the cyclic loads of the shock absorber. The fracture surface exhibited clear fatigue characteristics, including smooth areas from oscillating contact and concentric-like fatigue rings, as well as traces of corrosion near the outer edge. The final stage of the failure was a sudden, brittle fracture without plastic deformation.
Findings
- The primary cause of the incident was the fatigue failure of the nose gear shock absorber pin caused by prolonged cyclic loading.
- The pin had been in service since May 12, 2017, and had undergone 9,926 landings prior to the incident, with over 95% of these being training flights.
- The fatigue crack was initiated at a stress concentrator (the thread) where the crushed threads had increased the pin's play within the fork.
- The uneven grass runway surface acted as a contributing factor to the mechanical stress.
- The aircraft's primary use for flight training contributed to the high frequency of landing cycles.
- The specific location of the pin made it impossible to detect the degradation during routine maintenance inspections.
Safety action
A new task has been introduced to the Maintenance Program for Tecnam P2002 JF aircraft: the replacement of the nose gear shock absorber pin and the nose gear fork pin must now be performed every 100 flight hours or once per year, whichever occurs first.