On May 8, 2001, a Cessna 170B (registration N3143A) was involved in an aviation accident near Fairbanks, AK. Investigators recorded the probable cause as: Failure of the tailwheel spring assembly at a preexisting crack. This summary draws on records from the U.S. National Transportation Safety Board (NTSB) historical archive.
During a wheel landing on a gravel runway, the tailwheel assembly broke off due to a preexisting crack in the spring assembly, causing rudder damage.
Accident Details
A commercial certificated pilot/flight instructor was conducting a local area instructional flight with the student pilot/airplane owner. The instructor reported performing wheel landings with the student on a gravel runway. During the touchdown of the third or fourth landing, the tailwheel assembly suddenly separated from the airplane.
Findings
An FAA airworthiness inspector examined the aircraft after the accident and discovered a preexisting crack in the tailwheel spring assembly. The crack was approximately 1/16 inch deep and 1/2 inch long. The spring failed at the crack. Upon departure, the tailwheel struck the bottom of the rudder and the rudder trim tab, tearing open the bottom and aft portion of the rudder assembly. The spring assembly had accumulated 126 hours total time, with 65 hours since the last annual inspection.
Probable cause
Failure of the tailwheel spring assembly at a preexisting crack.