INEXPERIENCED STUDENT PLT; UNFAMILIAR WITH THE AUTOPLT IN THE C172; MAKES OFF FIELD LANDING WHEN IT ENGAGES; LEADING HIM TO CONCLUDE HE WAS EXPERIENCING A MALFUNCTION OF THE FLT CONTROLS.

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CLBING TO 2500 FT MSL AND HDG NW; I WAS BOUND FOR THE FAR N END OF THE LAKE TO PRACTICE MANEUVERS IN PREPARATION FOR MY PVT PLT CHK RIDE. AS I BEGAN TO SET UP IN PREPARATION FOR THE PRACTICE; MY ACFT SUDDENLY ENTERED A 20-30 DEG R BANK; WITHOUT MY INPUT. I OVERCAME THE CTLS AND RETURNED THE WINGS TO LEVEL; AT WHICH TIME THE ACFT AGAIN BEGAN TO BANK R. I OVERCAME THE INPUT AGAIN AND IMMEDIATELY BEGAN LOOKING FOR AN EMER LNDG SPOT AS I FELT THE ACFT COULD BECOME UNCTLABLE AT ANY MOMENT. THE CTLS CONTINUED TO ATTEMPT TURN THE ACFT TO THE R; HOWEVER; I CALLED MAYDAY; MAYDAY ON ZZZ UNICOM; STATED THAT I WAS OVER THE N END OF THE LAKE AND WAS GOING DOWN. I SAW 2 POSSIBLE LNDG SITES; ONE OF WHICH WAS A ROAD SURROUNDED BY TREES; AND THE OTHER A SHORT STREET THAT APPEARED TO HAVE FEW IF ANY HOMES OR OBSTRUCTIONS. I MADE THE DECISION TO LAND ON THE STREET; BEGAN A DSCNT WHILE CTLING THE ACFT; AND LANDED WITHOUT INCIDENT. I TAXIED THE ACFT INTO A GRASSY AREA OFF THE ROAD; SHUT DOWN ACCORDING TO THE CHKLIST; AND EXITED THE ACFT. ALL UTILITIES IN THE AREA WERE UNDERGROUND AND THERE WAS ONLY 1 HOME ON THE STREET. I USED THE 1 HOMEOWNER'S PHONE TO CALL THE FBO; AS I HAD NO CELL PHONE SVC IN THIS REMOTE LOCATION. I NOTIFIED THEM I HAD LANDED WITH NO DAMAGE TO THE ACFT AND THEY BEGAN NOTIFYING EVERYONE NECESSARY. AFTER THE OPS MGR ARRIVED HE STATED HE FELT THAT I HAD INADVERTENTLY ENGAGED THE AUTOPLT. I CHKED THE AUTOPLT SWITCHES AND BOTH WERE IN THE 'OFF' POS. AN INSTRUCTOR PLT ARRIVED; AFTER CLRNC FROM THE FAA REPRESENTATIVE; DISABLED THE AUTOPLT BY PULLING THE CIRCUIT BREAKER OUT AND FLEW THE ACFT BACK TO ZZZ. IN RETROSPECT; I WISH I HAD BEEN FAMILIAR WITH THE AUTOPLT OP AND WHAT MIGHT HAPPEN IF IT WERE INADVERTENTLY ENGAGED. I HAVE NEVER FLOWN THE ACFT WITH THE AUTOPLT ENGAGED AND WAS ONLY MINIMALLY AWARE THE ACFT EVEN HAD ONE. I AM CERTAINLY AWARE OF WHAT CAN HAPPEN NOW AND I KNOW WHERE THE CIRCUIT BREAKER IS LOCATED IF NEEDED. THE WX AT THIS TIME WAS CLR; VISIBILITY WAS EXCELLENT AND NO DAMAGE OCCURRED TO THE ACFT OR PROPERTY; AND NO INJURY TO ANY PERSON. SUPPLEMENTAL INFO FROM ACN 770804: SINCE THE OCCURRENCE; I HAVE PERSONALLY CHANGED MY TRAINING PROCS TO INCLUDE; EARLY ON IN TRAINING; THE USE AND DISABLING OF AUTOPLTS INSTALLED IN ANY ACFT I CONDUCT TRAINING IN.