What happened
On 8 March 2020, a Cessna 180 (registration ZS-TIO) was conducting a private flight from Kitty Hawk Aerodrome to Baragwannath Aerodrome in Gauteng. During the approach to Runway 13, the aircraft was flying at approximately 70 knots with the first notch of flaps extended.
Upon touchdown, the aircraft experienced a hard landing. Immediately before the tail wheel made contact with the runway, a severe vibration was felt. The aircraft subsequently veered right of the runway centerline and onto the grass. The nose of the aircraft struck the ground, leaving the aircraft resting on the right edge of the runway with the left wing low. While the aircraft sustained substantial damage to the fuselage, propeller, engine cowling, and left wing, there were no injuries to the pilot or the passenger.
The investigation
SACAA AIID investigators examined the left main landing gear assembly to determine the cause of the aircraft's instability during the landing roll. The inspection of the gear assembly revealed that the bolts and nuts responsible for securing the axle to the left gear struts had failed.
Specifically, the investigation found that of the four bolts and nuts used to secure the axle to the strut, two remained attached, one bolt had snapped, and a fourth bolt was missing entirely. The two rear bolts showed evidence of being sheared and bent, with fracture surfaces consistent with an overstress fracture.
Maintenance records indicated that the aircraft's last 100-hour Mandatory Periodic Inspection had been completed approximately 24 hours of flight time prior to the accident. While the maintenance organization performed visual inspections of the components, the investigation noted that these were not subjected to non-destructive testing (NDT).