What happened
The FAA’s narrative, in sentence case. The FAA writes it in capitals and removes private details.
The pilot reported that after an uneventful wheel landing in the tailwheel equipped airplane on R21L, he held the airplane’s tail off the ground until it had decelerated to about 30 mph. As soon as the tail settled, and the tailwheel touched the ground, the airplane ground looped aggressively.
The tailwheel likely hit a rut or bounced on touchdown causing the tailwheel lock to become disengaged. The now unlocked wheel likely oscillated to its travel limit, where the arm engaged with the sides of the pivot plate, locking it in place at 45 °. This would have resulted in the sudden loss of lateral control reported by the pilot.
As the FAA filed it
THE PILOT REPORTED THAT AFTER AN UNEVENTFUL WHEEL LANDING IN THE TAILWHEEL EQUIPPED AIRPLANE ON R21L, HE HELD THE AIRPLANE’S TAIL OFF THE GROUND UNTIL IT HAD DECELERATED TO ABOUT 30 MPH. AS SOON AS THE TAIL SETTLED, AND THE TAILWHEEL TOUCHED THE GROUND, THE AIRPLANE GROUND LOOPED AGGRESSIVELY.
THE TAILWHEEL LIKELY HIT A RUT OR BOUNCED ON TOUCHDOWN CAUSING THE TAILWHEEL LOCK TO BECOME DISENGAGED. THE NOW UNLOCKED WHEEL LIKELY OSCILLATED TO ITS TRAVEL LIMIT, WHERE THE ARM ENGAGED WITH THE SIDES OF THE PIVOT PLATE, LOCKING IT IN PLACE AT 45 °. THIS WOULD HAVE RESULTED IN THE SUDDEN LOSS OF LATERAL CONTROL REPORTED BY THE PILOT.
NTSB investigation
The NTSB’s investigation of this event, with its probable cause and findings. Matched to this report by N-number and date.