PLT OF AMERICAN YANKEE WITH TAILWHEEL CONVERSION HAS RWY EXCURSION ON LNDG DUE TO BROKEN TAILWHEEL CTL ARM.

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AFTER EXECUTING A 3 POINT LNDG AT PLK A SLIGHT VIBRATION WAS EXPERIENCED IN THE TAILWHEEL. VIBRATION INCREASED AND ACFT MADE A SHORT YAW TO THE L. AFTER APPROX 30 DEG YAW THE R LNDG GEAR ATTACH BRACKET BOLTS SHEARED AND R WING CONTACTED THE RWY. ACFT THEN SKIDDED TO THE R AND EXITED RWY TAIL FIRST. THE YAW EXPERIENCED WAS NOT CONTROLLABLE. NO INJURY TO OCCUPANTS OR PROPERTY DAMAGE INCURRED. INSPECTION OF TAILWHEEL BY IA REVEALED R CTL ARM ON TAILWHEEL BROKE CLEAN WITH EVIDENCE OF CORROSION AT BREAK. TAILWHEEL ASSEMBLY IS LANG P/N D-501A WITH 8 HRS AND 14 LNDGS SINCE NEW. NTSB FORM 6120-1/2 FILED. ACFT INVOLVED WAS AMERICAN YANKEE AA-1TW. WX WAS NOT A FACTOR. INSTALLATION OF MANUAL LOCKING TAILWHEEL WOULD ELIMINATE PROB. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: RPTR STATES THAT THE CTL ARM HAD BEEN ON THE ACFT ONLY 2 1/2 WKS. THERE IS SPECULATION THAT THE PART MIGHT BE FAULTY SINCE THE MECH ON SITE INDICATED IT HAD BEEN BROKEN PRIOR TO THE INCIDENT. IT WAS A STRESS PROB THAT CAUSED THE BREAK. SINCE IT TOOK 6 MONTHS ON BACK ORDER TO RECEIVE THE PART; RPTR SPECULATES THAT THIS WAS A NEW BATCH OF PARTS. HE HAS REQUESTED THE OLD PART FROM THE INSURANCE COMPANY AND WILL MATCH THIS WITH THE SPEC SHEETS TO EVALUATE THE PROB.