SMA X FLT OF 2 (BI-PLANE). BI-PLANE NONADHERENCE TO ATC CLRNC MADE UNAUTHORIZED 360 TURN ON FINAL APCH HAD NMAC WITH SMA Y SEQUENCED TO FOLLOW. PLTDEV.

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SMA Y OPERATED BY A FLT SCHOOL ON A TRAINING FLT. SMA X CALLED IN AS A FLT OF 2 AND WAS TOLD TO ENTER BASE. SMA Y ON THE DOWNWIND WAS SEQUENCING BEHIND THE FLT OF 2. ON FINAL THE SECOND ACFT OF THE FLT (A BIPLANE) BEGAN TO S- TURN FOR SPACING WITHOUT TELLING THE TWR. AN ACFT FOR DEP BEGAN A LONG NARRATIVE OF WHAT HE WANTED TO DO. THE BIPLANE MADE A TIGHT 360 DEG TURN ON FINAL AND TURNED BACK TO FINAL BENEATH SMA Y WHICH HAD CLBED AND TURNED TO AVOID COLLISION. THE DEP REQUEST DIDN'T EVEN END UNTIL AFTER THE 360 WAS COMPLETED. THE SMA Y PLT VOICED HIS DISPLEASURE OVER THE EVENT AND LANDED AFTER FLYING AROUND THE PATTERN. THE BIPLANE LANDED WITHOUT FURTHER INCIDENT AND WAS INSTRUCTED TO CALL THE TWR. AT THAT TIME HE GAVE HIS CALL SIGN; WHICH WAS THE FIRST TIME IT WAS AIRED. CORRECTIVE ACTIONS SEEMED; AT THE TIME; IMPOSSIBLE. THE FREQ WAS BLOCKED BY ANOTHER XMITTER AND THE CALL SIGN OF THE OFFENDING ACFT WAS UNKNOWN. IN RETROSPECT; IT IS LIKELY THE TWR XMITTER WOULD HAVE OVERRIDDEN THE OTHER RADIO AND SMA Y COULD HAVE BEEN WARNED EARLIER. THE BIPLANE PLT WAS TOLD OVER THE PHONE NOT TO CALL IN AS A FLT IF HE COULDN'T FLY AS A FLT; AND TO MAKE A NORMAL PATTERN IF HE HAD TO GAR.