C172 PLT; EXPERIENCES ENG FAILURE AND FORCED LNDG DUE TO FUEL STARVATION FROM MISTAKEN INFLT CALCULATIONS.

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IN MID-AFTERNOON STARTED PREPARING FOR TRANSPORTATION OF MY 2 OLDEST CHILDREN TO THEIR MOTHER'S LATEST RESIDENCE. REVIEWED LATEST WX INFO TO INCLUDE WINDS ALOFT OVER THE RTE. AS CUSTOMARY; 30 MINS BEFORE PLANNED DEP FROM FME; CONTACTED LEESBURG FLT SVC FOR STANDARD BRIEFING; FILING OF 'S&R' AND ADIZ FLT PLAN. USUALLY; I FLEW THE SAME C172/G ON THE RTE EVERY OTHER WK FOR THE PAST 3 MONTHS. ROUGHLY 20 MINS BEFORE PLANNED DEP AT XA00L; FLYING CLUB'S CHIEF INSTRUCTOR INFORMED ME HE WAS DOWNING THE ACFT I HAD RESERVED DUE TO COWLING FASTENERS FAILING DURING THIS TRAINING FLT. RESERVED A SIMILAR C172/A; WHICH WAS JUST BEING RETURNED FROM A DIFFERENT STUDENT PLT TRAINING FLT. CONTACTED LEESBURG FLT SVC TO AMENDED FLT PLAN FOR REPLACEMENT ACFT AND DIFFERENT NAVIGATIONAL RTE SELECTION (VOR VERSUS GPS PRIMARY NAV). DURING PREFLT THAT WAS JUST AFTER SUNSET; PERFORMED THE ENTIRE CHKLIST PREFLT PROCS INCLUDING CHKING FUEL IN TANKS. AT THAT TIME FUEL WAS AT NECK OF BOTH TANKS; WHICH I INTERPED AS FULL TANKS. DEPARTED FROM FME GOING TO JNX. NOTHING SIGNIFICANT TO RPT OTHER THAN GETTING STRONGER THAN EXPECTED TAILWINDS AT 6500 FT; THUS COMPLETING TRIP TO JNX ALMOST A HALF HR LESS THAN PLANNED. LNDG AT XA33. FLEW FROM JNX TO W96 AS USUAL. W96 IS MY NORMAL FUEL STOP FOR THE ROUND ROBIN. FLEW AT 2500 FT TO AVOID HIGH WINDS AT HIGHER ALT. TIME ENRTE WAS AS PLANNED. UPON LNDG; DISCOVERED ARPT MGMNT HAD POSTED A SIGN ON THE 24-HR FUEL PUMP SYS THAT IT WAS BROKEN. NO OTHER FUELING OPTIONS AT THE ARPT WERE APPARENT. REVIEWED FLT TIMES AND ESTIMATED FUEL BURNED BASED ON ENRTE CONSUMPTION RATE DISPLAYED ON FUEL FLOW GAUGE. APPLIED AN ADJUSTMENT FOR GND OPS AT LESS THAN CRUISE BURN RATE. BASED ON THOSE ESTIMATES; FIGURED A HIGH AND LOW RANGE FOR FUEL STILL ON BOARD (BTWN 1:24 AND 1:50 REMAINING). THOUGHT ABOUT STOPPING AT ANOTHER ARPT ALONG THE RTE; BUT 24-HR PUMPS WERE NOT NOTED DURING MY PRIOR RTE PLANNING SEVERAL WKS PRIOR. SINCE THE FINAL LEG OF THE TRIP FROM W96 TO FME WAS CALCULATED FOR A DURATION OF 57 MINS; WX PURE VMC; AND FAMILIAR WITH RTE FROM SEVERAL PRIOR TRIPS; ELECTED TO PROCEED WITHOUT FUELING. BELIEVED THE ESTIMATED FUEL RESERVE RANGE OF 27-53 MINS WOULD NEVER BE TAPPED. DEPARTED FROM W96 GOING TO FME. AS CUSTOMARY; CONTACTED LEESBURG FLT SVC VIA RADIO TO CLOSE PRIOR FLT PLAN; FILE/OPEN A S&R; AND FILE AN ADIZ FLT PLANS. PROVIDED THE 1 HR 50 MIN FUEL AVAILABLE NUMBER. AFTER CONTACTING ATC PROCEEDED INTO ADIZ AS USUAL. ABOUT 20 MINS INTO FLT NOTICED R TANK GAUGE MOVED QUICKLY FROM JUST UNDER HALF FULL TO JUST ABOVE EMPTY. ROUGHLY 6 MINS FROM FME; ENG LOST PWR SOUNDING MUCH LIKE FUEL STARVATION. R TANK GAUGE READ JUST ABOVE EMPTY. L TANK GAUGE READ ROUGHLY 1/8 FULL. WENT TO BEST GLIDE AND RAN THROUGH ENG FAILURE PROCS LESS MAGNETO CHK. DURING ENG FAILURE PROCS; PERFORMED A 170 DEG TURN TO GO BACK TOWARD A LIGHTED DIVIDED 4-LANE ROAD WITH AN INTERCHANGE. CONTACTED ATC TO NOTIFY THEM OF ENG FAILURE; APPROX LOCATION AND INTENTION TO LAND ON THE ROADWAY. RECEIVED ACKNOWLEDGEMENT AND WIND CONDITIONS FROM ATC. LANDED ACFT ON THE WBOUND LANES DUE TO SIGNIFICANTLY LESS TFC (ALMOST NONE) THAN EBOUND LANE. LNDG WAS A SMOOTH FULL FLAP LNDG. NO DAMAGE TO ACFT; PERSON OR THING OCCURRED. COASTED ACFT TO PAVED SHOULDER OF ROAD. RADIOED ATC WITH CONDITION OF ACFT; PERSON AND LOCATION RELATED TO ADW. PUSHED ACFT OFF THE PAVED SHOULDER ONTO THE GRASS TO AVOID WING CONTACTING A PASSING MOTOR VEHICLE. SECURED ACFT. WHEN FIRE DEPT SQUAD CAR ARRIVED; CONTACT FLYING CLUB MGMNT TO ADVISE THEM OF SIT. CONTACTED FLT SVC STATION TO CLOSE FLT PLAN. WHEN POLICE ARRIVED; COOPERATED WITH THEIR INVESTIGATION. POLICE TELEPHONED BWI ADMINISTRATOR FOR DIRECTIONS. REVIEW OF INFLTS NOTES: APPARENTLY; GRABBED A TIME DURATION ON THE FIRST LEG OF THE TRIP FROM THE WRONG SPOT ON THE NOTEPAD. RESULTED IN NOT ACCOUNTING FOR ROUGHLY 23 MINS OF FLT TIME. WORSE CASE FUEL ESTIMATE AT W96 CORRECT OUTSIDE OF MISSING 23 MINS OF FUEL BURN. CONCLUSIONS: 1) NEVER BELIEVE A FUEL TANK IS COMPLETELY FULL UNLESS YOU FILLED IT YOURSELF AND BURPED THE TANKS. AS A RULE OF THUMB; DON'T TRUST THE LAST HR OF FUEL ON BOARD. 2) ALWAYS CHK NOTAMS FOR ARPTS; EVEN THE FAMILIAR ONES. 3) FUEL QUANTITY AND FLOW GAUGES ON AN ACFT ARE INHERENTLY UNRELIABLE. THEY DON'T READ CORRECTLY EVEN WHEN THE TANK IS EMPTY. 4) SAFER TO BE PESSIMISTIC THAN VENTURE INTO OPTIMISTIC WORLD ESPECIALLY WHEN YOU ARE CONSERVATIVE BY NATURE. 5) WRITE CLRLY AND DOUBLE CHK CALCULATIONS AND SOURCES OF KEY INFO. 6) A SERIES OF MINOR EVENTS CAN LEAD TO A BIGGER PROB.