What happened
On March 4, 2016, during a routine inspection of the landing gear on a Cessna 172S, registration SP-MMD, maintenance personnel discovered damage to the lower surface of the left main landing gear strut. The damage was located just above the strut's bend, specifically above the wheel axle attachment point. The inspection revealed scratches and a mechanical indentation measuring approximately 0.5 mm (0.020 inches) in depth. The damage was not corrosive in nature but was strictly mechanical.
The investigation
The investigation, conducted by FLY Bielsko Usługi Lotnicze, determined that the damage was caused by physical contact between the landing gear strut and specific bolts (P/N S1021Z6-6). These bolts are used to secure the front and rear sections of the wheel and brake fairing (P/N 0541224-1). The investigation established that the bolts were long enough to strike the strut during operation. At the time of the incident, the aircraft had accumulated 488.8 flight hours since its manufacture in 2008.
Findings
- The direct cause of the damage was the improper selection of bolt length by the aircraft manufacturer.
- The mechanical contact between the P/N S1021Z6-6 bolts and the lower surface of the landing gear strut resulted in the identified scratches and indentation.
Safety action
Following the discovery of the damage, the operator notified both the aircraft manufacturer and the European Union Aviation Safety Agency (EASA). The damage was reported to the manufacturer to determine whether the strut could be repaired or if a complete replacement would be required.