Stinson 108 N343C accident near Haines, Alaska

Probable cause

The pilot’s failure to maintain directional control of the airplane during the landing roll with a quartering tailwind, which resulted in a ground loop and overstress failure of the left main landing gear wheel axle.

NTSB analysis

The private pilot stated that, during the landing roll in the tailwheel-equipped airplane, he started a right turn to exit the runway using a high-speed taxiway when the airplane had slowed to about 20 mph. During the exit, the airplane made an abrupt right turn that the pilot could not control with left rudder and brake. The left wheel axle fractured, followed by a collapse of the left landing gear leg, which resulted in substantial damage to the airplane. The reported wind was a left quartering tailwind of 4 knots. The pilot and passenger observed variable gusting wind immediately after the accident. Postaccident examination after recovery of the wreckage found that the tailwheel attachment bracket was fractured.

An examination of the left main landing gear axle weld fracture with a scanning electron microscope (SEM) revealed features consistent with tensile overstress that would have occurred during the accident sequence.

An examination of the airframe tailwheel mount fracture surface with a SEM revealed signatures consistent with overstress failure, and other fracture areas of widespread corrosion.

Photographs taken before the airplane was removed from the runway showed the tailwheel assembly in its normal position, with no abnormalities visible. Also, during the recovery of the airplane, no tailwheel separation or abnormal function was observed. Based on the examinations of the fractured components, there is no evidence that the fracture of the tailwheel mount led to a displacement of the tailwheel assembly or a loss of control during the landing.

Based upon the pilot and passenger's statements regarding wind at the accident site, it is possible that an unexpected gust of quartering tailwind initiated a loss of control, and the high groundspeed and heavy landing weight contributed to increased lateral loads on the left landing gear during the ground loop, which resulted in overload failures of the axle and tail bracket welds.

Text from the NTSB. Open the NTSB docket for ANC16LA048 for the full record.