What happened
On May 28, 2014, at approximately 19:20 LMT, a Cessna A185F Skywagon, registration HA-SVH, was taxiing toward runway 16 at Krosno Airport [EPKR] for a skydiving operation. The aircraft was performing its second flight of the day with a crew of six.
After taxiing approximately 300 meters, a loud bang occurred, and the pilot observed the left main tire separating from the wheel and flying toward the propeller. The tire struck the propeller blades and was thrown approximately 30 meters away. The pilot immediately reduced power, shut down the engine, and deactivated the ignition, electrical systems, and fuel valve. The aircraft drifted approximately 2.5 meters before coming to a stop. No injuries were reported among the six occupants.
The investigation
Investigators examined the wreckage and found that the retaining ring holding the tire to the wheel hub had detached, along with three mounting bolts. The investigation revealed that the threads within all six mounting holes in the wheel hub had been stripped, and a small fragment of the aluminum hub had broken off near one of the bolt holes.
While the steel bolts themselves remained undamaged, the presence of aluminum material on the bolt threads indicated that the internal threads of the hub had failed. The investigation could not definitively determine when the damage occurred, but it was most likely during the most recent tire change. The propeller also sustained damage, including two bent blades and the loss of sealing rings from the blade base.
Findings
- The primary cause of the incident was the application of excessive torque when tightening the bolts that secure the tire retaining ring to the hub.
- The higher strength of the steel bolts compared to the aluminum hub caused the hub threads to strip under the high torque load.
- The separation of the tire led to the subsequent contact between the tire and the propeller blades.