What happened
On June 30, 2018, a Cessna 180D, registration PT-BMZ, was performing a series of skydiving operations at the Torres Aerodrome (SBTR) in Rio Grande do Sul, Brazil. The aircraft, carrying a pilot and four skydivers, climbed to 10,000 feet for a scheduled jump. However, the pilot lost visual contact with the runway due to a low cloud layer covering the aerodrome, forcing the cancellation of the jump.
During the subsequent descent, the pilot attempted to land on runway 05. The approach was unstabilized and featured a tailwind, resulting in a long, high-speed touchdown and a bounced landing. After performing a go-around, the pilot attempted a second landing on runway 23. This approach was also unstabilized. During the landing sequence, the aircraft experienced multiple touchdowns, at which point the right main landing gear strut fractured. This caused the aircraft to veer right and exit the runway onto the grass, resulting in substantial damage to the aircraft. All five occupants were unharmed.
The investigation
CENIPA investigators examined the aircraft's maintenance records and the physical condition of the failed component. While the aircraft's maintenance logs were up to date and the annual inspection had been performed recently, the investigation focused on the structural integrity of the landing gear. Laboratory analysis of the fractured right main landing gear strut revealed a 1.47 mm deep pre-crack, secondary cracks, and multiple areas of corrosion hidden beneath the paint.
Furthermore, the investigation reviewed the aircraft's weight and balance. At takeoff, the aircraft weighed 1,360 kg, which was 38 kg above its maximum certified takeoff weight of 1,322 kg. Even after accounting for fuel burn, the aircraft remained approximately 18 kg over the maximum allowable limit during the landing attempt.
Findings
- The right main landing gear strut was weakened by corrosion located beneath the paint, which led to the development of cracks.
- The aircraft was operating above its maximum certified takeoff weight.
- The structural stresses caused by the unstabilized landing attempts likely exceeded the limits of the already compromised component.
- Flight planning, pilot judgment, and aircraft maneuvering contributed to the occurrence.