On May 7, 2001, at 1956 Alaska daylight time, a wheel-equipped Cessna 170B airplane, N3143A, sustained substantial damage during landing at the Fairbanks International Airport, Fairbanks, Alaska. The airplane was being operated as a visual flight rules (VFR) local area instructional flight when the accident occurred. The airplane was operated by the student pilot/owner. The commercial certificated pilot/flight instructor, and the student pilot, were not injured. Visual meteorological conditions prevailed. The flight originated at the Fairbanks International Airport at 1917. During a telephone conversation with the National Transportation Safety Board (NTSB) investigator-in-charge (IIC), on May 9, 2001, the flight instructor reported that he was seated in the right seat, and was conducting wheel landings with the student on the ski strip, runway 19, at Fairbanks. During the touchdown on the third or fourth landing, the tailwheel assembly suddenly broke off. A Federal Aviation Administration (FAA) airworthiness inspector, Fairbanks Flight Standards District Office (FSDO), examined the airplane after the accident. He reported he found a preexisting crack in the tailwheel spring assembly that was about 1/16 inch deep, and about 1/2 inch long. He said the spring failed at the crack, and when the tailwheel departed the airplane, it struck the bottom of the rudder, and the rudder trim tab. The bottom and aft portion of the rudder assembly was torn open. In the Pilot/Operator Report (NTSB form 6120.1/2) submitted by the student pilot/owner, the owner indicated the tailwheel spring had a total time of 162 hours. The 6120.1/2 report noted an annual inspection was conducted on November 6, 2000, 65 hours before the accident.