A LOW TIME PVT PLT LANDS HIS C172 ON AN INTERSTATE HWY WHEN THE ENG STOPS DUE TO FUEL EXHAUSTION.

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THIS INCIDENT OCCURRED ON OCT/XA/01 AND INVOLVED A FUEL STARVATION ENG OUT LNDG ON INTERSTATE XX; IN A C172. THERE WAS NO INJURY TO PERSONS NOR WAS THERE ANY DAMAGE TO ANY PROPERTY. IT IS MY UNDERSTANDING THAT THE ACFT INVOLVED ALSO SUSTAINED NO DAMAGE AT ALL AND WAS RETURNED TO SVC WITHIN A FEW DAYS AFTER THE OCCURRENCE. WX WAS NOT A FACTOR AS IT WAS A BEAUTIFUL DAY WITH CLR SKIES; AND MINIMAL SURFACE WINDS. FORECAST WINDS AT LOWER ALTS WERE GENERALLY OUT OF THE SW. THE PLANNED FLT WAS ROUND TRIP FROM ZZZ ARPT DIRECT TO ZZZ1 ARPT DEPARTING AT XA00 AND DIRECT BACK TO ZZZ THAT AFTERNOON AT XJ00. I PERFORMED THOROUGH PREFLT PLANNING WHICH INCLUDED WT AND BAL; COMPUTATION OF WIND; GND SPD AND ESTIMATED TIMES ENRTE FOR EACH LEG OF THE FLT. MY PREFLT PLANNING DETERMINED THAT THE FLT FROM ZZZ TO ZZZ1 WOULD TAKE JUST UNDER 2 HRS. I CALCULATED THE RETURN FLT TO TAKE 1 HR 40 MINS. THEREFORE; I CALCULATED THE ENTIRE ROUND TRIP TO TAKE 3 HRS 40 MINS. I GENERALLY PLAN FUEL BURN CONSERVATIVELY IN THE C172; WHICH CARRIES 40 GALLONS OF USABLE FUEL. I PLAN FOR A FUEL BURN OF 9 GPH. THUS; AT A CONSERVATIVE 9 GPH FUEL BURN; I SHOULD HAVE HAD 4 HRS 24 MINS WORTH OF FUEL ON BOARD. THE FLT WAS IN A RENTED C172N WITH 2 21.5 GALLON FUEL TANKS WITH APPROX 40 USABLE GALLONS. PRIOR TO DEP; I PERFORMED A THOROUGH PREFLT INSPECTION OF THE ENTIRE ACFT. DURING THE COURSE OF THE PREFLT; I VISUALLY CHKED BOTH WING TANKS AND FOUND THE R TANK FULL TO THE POINT OF ALMOST SPILLING OUT AND THE L TANK FULL TO THE FUEL TANK COLLAR. THE ACTUAL LEG FROM ZZZ TO ZZZ1 TOOK JUST UNDER 2 HRS; AS PLANNED. FUEL BURN SHOULD HAVE BEEN A TOTAL OF ABOUT 18 GALLONS FOR THE FIRST LEG; WHICH WOULD HAVE LEFT ABOUT 22 GALLONS (2 HRS 24 MINS) OF FUEL REMAINING FOR THE RETURN FLT; WHICH I PLANNED WOULD TAKE ABOUT 1 HR 40 MINS DUE TO THE TAILWIND. I CALCULATED THAT I WOULD HAVE ABOUT 45 MINS OF RESERVE FUEL UPON COMPLETION OF THE TRIP BACK AT ZZZ. THE RETURN FLT BEGAN UNEVENTFULLY; LEVELING OFF AT 3500 FT MSL TO TAKE ADVANTAGE OF STRONGER WINDS. APPROX 1 HR 25 MINS INTO THE FLT; 10 MI SW OF THE TOWN OF ZZZ2; THE ENG STOPPED. OUT OF HABIT I PITCHED UP FOR 70 KTS AND BEFORE I WAS ABLE TO TRY AND RESTART THE PLANE; IT STARTED ON ITS OWN. ZZZ2 ARPT WAS LESS THAN 2 MI NE OF TOWN AND WITH THE ENG RUNNING AGAIN I MADE A DETERMINATION TO PUT DOWN THERE TO DETERMINE THE CAUSE OF THE ENG FAILURE. LESS THAN 10 SECONDS AFTER ENG QUIT THE FIRST TIME IT STOPPED AGAIN. I PUSHED IN THE MIXTURE AND THE PLANE RESTARTED FOR THE SECOND TIME. THE ENG SEEMED TO START AND STOP AT LEAST 7 TIMES AT WHICH TIME IT WOULD NOT RESTART. WITH LESS THAN 2500 FT AGL; I DETERMINED WE COULD NOT MAKE THE FIELD AND IMMEDIATELY STARTED LOOKING FOR A SUITABLE LNDG SITE. I COULD NOT FIND A LARGE ENOUGH FIELD THAT I FELT COMFORTABLE SETTING THE PLANE DOWN ON; YET A LARGE 4-LANE HWY LAY LESS THAN 2 MI AHEAD. APCHING INTERSTATE HWY XX; MY FIRST THOUGHT WAS TO LAND WITH THE TFC HDG WBOUND BUT I SAW TOO MANY SETS OF PWR LINES. I TURNED R AND WITH A SLIGHT TAILWIND SET UP TO LAND WITH THE TFC HDG EBOUND. I LANDED IN THE FAST LANE OF EBOUND TFC; SETTING DOWN WITH THE STALL HORN BLARING. AT WHAT SEEMED LIKE 25-30 KTS; I MOVED THE PLANE INTO THE GRASS MEDIAN TO AVOID ANY APCHING TFC FROM THE REAR. I CERTAINLY CANNOT EXPLAIN WHY THE ACFT RAN OUT OF FUEL AFTER ONLY FLYING 3.5 HRS; WHEN IT SHOULD HAVE HAD A SOLID HR OF FUEL REMAINING IN THE TANKS. THE ONLY EXPLANATIONS I CAN OFFER ARE THE FOLLOWING: 1) THE ACFT HAD SOME TYPE OF FUEL LEAK; OR 2) THE ACFT WAS BURNING FAR MORE FUEL THAN IS SPECIFIED IN THE ACFT FLT MANUAL/PLT HANDBOOK. IN TERMS OF THINGS THAT COULD HAVE BEEN DONE TO PREVENT THE OCCURRENCE; I COULD HAVE MANUALLY CHKED THE FUEL TANKS WHILE IN ZZZ1 BEFORE MAKING THE RETURN FLT WITH A FUEL INDICATOR TUBE. THIS MAY HAVE INDICATED A POSSIBLE FUEL LEAK OR UNUSUALLY HIGH FUEL BURN ON THAT LEG. I DID NOT DO THIS BECAUSE I VISUALLY VERIFIED THAT WE HAD FULL FUEL TANKS UPON LEAVING ZZZ AND MY PREFLT PLANNING DETERMINED THAT WE SHOULDHAVE HAD ABOUT 45 MINS OF FUEL REMAINING UPON THE COMPLETION OF THE FLT BACK AT ZZZ.