What happened
On July 19, 2019, a private flight involving a Tecnam P2008 JC, registration HB-KMJ, experienced a serious incident during landing at the Sitterdorf airfield in Switzerland. The aircraft, operated by Flugschule Basel AG, was performing a routine VFR flight from St. Gallen-Altenrhein to Sitterdorf.
As the aircraft crossed the threshold of the 480-meter grass runway, its speed was recorded at approximately 63 knots, which was higher than the manufacturer's recommended approach speed of 55 KIAS. Upon touchdown, the nose gear strut failed and separated from the aircraft, causing the nose to drop onto the runway. The aircraft continued to roll briefly before coming to a halt. There were no injuries to the two occupants, though the aircraft sustained light damage.
The investigation
Investigators from SUST examined the wreckage of the nose gear assembly and conducted a detailed metallurgical analysis. The investigation focused on the structural integrity of the nose gear leg, specifically the area where a steel plate reinforcement was welded to the main tube.
Microscopic examination using scanning electron microscopy revealed the presence of fatigue striations and intercrystalline cracks. The analysis determined that the failure was not caused by a single high-impact event, but rather by a progressive fatigue fracture. Furthermore, investigators found that the steering movement of the nose gear strut was restricted due to an excessively high torque on a bolt connection, which increased the stress on the weld.
Findings
- The primary cause of the incident was a failure of the nose gear leg due to a defective weld.
- The fracture was an fatigue-induced failure (Schwingbruch) that originated from flaws in the welding process.
- The aircraft's approach speed was higher than the manufacturer's recommended 55 KIAS.
- Metallurgical testing confirmed that the weld contained hot cracks and intercrystalline damage.
- The nose gear assembly had been previously repaired with a non-identical reinforced part following a similar incident in 2015.
- The manufacturer had issued several Service Bulletins regarding nose gear inspections and reinforcements following similar documented incidents in other aircraft.