On October 26, 2005, about 1630 central daylight time, a Taylorcraft BC12-D, N39216, operated by an airline transport pilot, sustained substantial damage when the airplane exited the runway during landing and nosed over on impact with a standpipe at a private airpark near St Marys, Kansas. The instructional flight was operating under 14 Code of Federal Regulations Part 91. Visual meteorological conditions prevailed at the time of the accident. No flight plan was on file. The pilot and certified flight instructor (CFI) reported sustaining minor injuries. The local flight originated from the airpark about 1530. The CFI's accident report, in part, stated: At the request for a Part 61.56 BFR (Biennial Flight Review) [the pilot], (a retired 20,000 hour airline captain) and I met at the St. Marys Airpark (FAA designation applied for but not yet issued) at approximately 2 PM. The Airpark has recently been constructed on an unimproved agricultural landing strip and is still being improved and widened. The only runway is 18-36, grass runway, approximately 2400 feet and 45 varying to 50 feet wide. The wind at the time was about SWerly 10 -12 knots. The runway surface is somewhat like the rough (clumpy) grass areas immediately adjacent to a golf course's fairway, which then changes into the more rough taller grass growth. There is a slight left bend (approx. 5 degrees) in the runway alignment starting at the mid point. The BFR was scheduled to be performed in a Taylorcraft tail wheel type airplane. After satisfactorily completing Section 61.56 (a) it was agreed that the applicant would also demonstrate competence in accordance with Section 61.31 (i) by performing at least six takeoffs and landings, three of which would be full stall three point landings and three wheel landings. The applicant, sitting in the left seat, after completing the air work tasks, which were fully in conformance with PTS limits, the previously agreed to landing sequence was started. The first two were satisfactory although the candidate had to be cautioned to be more aggressive in staying closer to the runway center lines. The landing prior to the incident was a (near perfect) wheel (tail up) landing on, and continue to track the runway centerline during roll out. The next approach and landing proceeded normally. Touch down was on center line, but during the rollout, [the pilot] let the airplane drift toward the runway left side. When cautioned he started to initiate a correction back to center. While [the pilot] was slowly correcting back, and at approximately 10-12 mph, the left main wheel passed through a small clump of thick grass growth causing the airplane to slew to left. Before I was able to react, the airplane veered off into the more heavy grass growth, where the main gear cross strut collided with a short vertical stand pipe, hidden in taller grass, causing the airplane to slowly nose over on its back. The CFI stated that there were no mechanical malfunctions with the airplane in reference to the flight. His safety recommendation stated, "As instructor I should have acted earlier [and] more aggressively."