A NAVION MADE AN OFF FIELD LNDG AFTER FUEL STARVATION CAUSED THE ENG TO QUIT.

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ON A VFR FLT ON MAY/SUN/05 AT XA28; IT WAS NECESSARY TO MAKE A FORCED LNDG IN A FIELD DUE TO THE ENG SPUTTERING AND EVENTUALLY CEASING TO OPERATE. I MADE A PWR-OFF LNDG IN A FIELD WITHOUT INCIDENT. NO INJURIES OR DAMAGE TO THE ACFT OR PROPERTY. A VISUAL INSPECTION OF THE FUEL TANK SHOWED NO VISIBLE FUEL AND THE INDICATIONS LEADING TO THE ENG STOPPING WERE CONSISTENT WITH FUEL STARVATION. PRIOR TO DEP; I HAD ESTIMATED 2 HRS FUEL ON BOARD BASED UPON HRS FLOWN SINCE LAST REFUELING. THE FUEL GAUGE INDICATED APPROX 1/4 FULL WHEN THE ENG DIED. AFTER OBTAINING 15 GALLONS OF 100LL FROM THE ARPT AT ZZZ; THE ACFT WAS TAKEN OFF WITHOUT INCIDENT AND REFUELED AT ZZZ WITH NO FURTHER INCIDENT. CAUSES: I BELIEVE THE PRIMARY CAUSE WAS MISCALCULATING THE FUEL ON BOARD PRIOR TO THE FLT. IN RECHKING MY FIGURES; I HAD MADE A SUBTRACTION ERROR THAT WAS 1 HR OFF FROM THE ACTUAL TIME FLOWN FROM LAST REFUELING; INSTEAD OF 2 HRS FUEL ON BOARD I HAD 1 HR. A CONTRIBUTING FACTOR WAS MY FAILURE TO TOP OFF MY FUEL PRIOR TO DEP AS IS MY NORMAL PRACTICE. AN ADDITIONAL FACTOR; ALTHOUGH NOT DIRECTLY CONTRIBUTING TO THE PROB WAS THAT THE FUEL GAUGE WAS NOT READING CORRECTLY; INDICATING AT LEAST 1/4 FULL WHEN THE ENG DIED. CORRECTIVE ACTIONS/LESSONS: 1) DOUBLECHK FUEL CALCULATIONS PRIOR TO ANY DEP. 2) ALWAYS TOP OFF THE FUEL WHEN POSSIBLE PRIOR TO DEP; ESPECIALLY FOR A TRIP. 3) HAVE CONTACTED MY MECH TO HAVE THE FUEL GAUGE CHKED AND FIXED OR REPLACED.