What happened
On August 15, 2006, a Cessna 150H, registration OK-CTD, was performing a navigational flight with takeoff and landing at Strunkovice Airport (LKST). Following the landing on runway 15, the aircraft continued along the runway for approximately 70 meters. At this point, the pilot reported hearing two distinct loud cracks. After traveling an additional 50 meters, the aircraft came to a halt in the southeastern portion of the runway.
The failure of the right landing gear strut caused the strut to break approximately 95 mm from its attachment point to the fuselage. The separated component, including the wheel and brake, came to rest about 27 meters behind the aircraft. The structural failure also caused the right side of the horizontal stabilizer to collide with the collapsing gear, resulting in damage to the tail section. There were no injuries to the pilot or any other persons.
The investigation
The ÚZPLN investigation focused on the structural integrity of the landing gear and the maintenance history of the aircraft. Laboratory analysis of the fracture surfaces was conducted by VZLÚ a.s. Prague. The investigation examined the manufacturing and surface treatment of the strut, as well as the maintenance protocols for the Cessna 150/152 series.
Investigators found that while the aircraft's airworthiness documentation and insurance were valid, the previous foreign operator had not recorded the total number of landing cycles. Based on the total airframe time, the number of landings was estimated to be approximately 27,290. Furthermore, the manufacturer's maintenance manual for this aircraft type does not mandate non-destructive testing (NDT) for landing gear components.
Findings
- The primary cause of the accident was the separation of the right landing gear strut due to a hidden material defect.
- Metallurgical analysis confirmed that fatigue failure occurred gradually during the aircraft's operation. The final fracture occurred during the landing rollout when the remaining cross-section could no longer support the operational loads.
- The fatigue crack originated from a surface irregularity on the underside of the strut (surface B) that was located beneath the paint layer. This area had not been surface-treated prior to painting, leaving residual corrosion products and irregularities.
- The landing gear strut is subject to bending stresses, and the presence of this unaddressed surface defect served as the initiation point for the fatigue crack.
- The pilot was unable to prevent the occurrence of the accident.