PLT FLIES WITH INADEQUATE FUEL SUPPLY IN IMC CONDITIONS.

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DESCRIPTION OF POSSIBLE INADEQUATE FUEL SIT ON FEB/KK/95. ON THE NIGHT OF FEB/KK/95; I DEPARTED ON A SCHEDULED CARGO RUN IN AN AERO COMMANDER 680FL (AC68). IT WAS MY FIRST TIME ON THIS PARTICULAR RUN. AS PART OF MY PREPARATION I TALKED WITH A PLT WHO NORMALLY FLIES THE RUN; AND THE COMPANY DIRECTOR OF TRAINING. I HAD PREVIOUSLY FLOWN INTO ALL OF THE ARPTS EXCEPT 1; AND I FLEW THE AC68 REGULARLY. I MADE NORMAL PREFLT PLANNING PREPARATIONS; AND I FELT COMFORTABLE ABOUT THE FLT. THE RTE NORMALLY HAS 3 STOPS. NORMALLY WE DROP OFF AND PICK UP CARGO AT ALL POINTS AND TAKE ON FUEL AT THE FIRST. ON THIS EVENING; THE FIRST STOP WAS FORECAST TO GO AS LOW AS 100 OVCST; WITH POSSIBLE LIGHT TO MODERATE ICE IN THE CLOUDS. THERE WAS NO CARGO FOR THAT STOP AND THE LATEST HRLY SHOWED 300 OVCST; LIGHT RAIN AND A SURFACE TEMP NEAR FREEZING. I WAS CONCERNED ABOUT ICE. I ELECTED TO ADD FUEL AFTER THE ACFT WAS LOADED AND OVERFLY THIS ARPT. DURING MY WX BRIEF I DESIGNATED CHEYENNE; WY AS THE ALTERNATE. I TOOK OFF WITH A TOTAL OF 815 LBS OR 135.8 GALLONS OF USABLE FUEL ONBOARD. USING THE LEAN BURN TECHNIQUE FOR THE LYCOMING IGSO-540 RECOMMENDED BY THE MANUFACTURER; THE AC68 WILL BURN LESS THAN 32 GALLONS/HR IN CRUISE. THE TOTAL DISTANCE FROM THE DEP TO CHEYENNE IS 440 NM. THE WINDS ALOFT FORECAST SHOWED THAT I WOULD HAVE A HEADWIND OF 5-15 KTS AT THE ALTS I WOULD BE FLYING. THE CRUISING SPD OF THE AC68 IN LEAN BURN IS ABOUT 155 NM/HR. THE FLT TIME FOR THE TOTAL TRIP WAS: 440 NM (155 NM/HR-15 NM/HR) = 3.14 HRS. I ALSO COMPUTED THE TIME USING THE COMPANY LOG SHEET. THESE TIMES ARE FROM ENG START TO ENG SHUTDOWN AND THEY ARE BASED ON YRS OF EXPERIENCE FLYING THIS RUN. ACCORDING TO THE COMPANY LOG SHEET; THE START TO STOP TIMES ADDED UP TO 2 HRS AND 45 MINS. USING THE COMPANY NUMBERS AND ADDING 51 MINS FOR MY FLT TO THE ALTERNATE; I ESTIMATED THE TOTAL TRIP AT 3 HRS AND 36 MINS. WITH THE USABLE FUEL THAT I HAD ON BOARD I ESTIMATED THAT I HAD: 135.8 GAL/32 GAL/HR = 4.24 HRS OF OP. USING THE MORE CONSERVATIVE LOG SHEET ESTIMATES; 48 MINS OF FUEL WOULD REMAIN ON BOARD AFTER GOING TO THE ALTERNATE. THE TRIP WAS UNEVENTFUL AND ON SCHEDULE UNTIL THE DEST. I SHOT THE VOR APCH TWICE AND MISSED BOTH TIMES. INSTEAD OF GOING TO THE ALTERNATE; I CHOSE TO RETURN TO THE PREVIOUS STOP. I HAD EASILY MADE IT IN ON THE ILS AN HR EARLIER; THE WX WAS ESSENTIALLY THE SAME; AND I WOULD HAVE A TAILWIND GOING BACK. THE DISTANCE WAS ONLY SLIGHTLY LONGER; 108 MI TO THE PREVIOUS STOP VERSES 102 MI TO THE ALTERNATE. ON THE WAY BACK; I HAD AN EMER. THE L ENG QUIT AFTER SWITCHING FROM THE AUX TANK TO THE CTR TANK. BOTH AUX TANKS WERE LOW WHEN I SWITCHED; BECAUSE I WAS TRYING TO LEAVE AS MUCH FUEL AS POSSIBLE IN THE CTR TANK FOR THE APCH AND LNDG. I WENT THROUGH THE ACFT EMER PROCS; AND ALLOWED SOME TIME FOR THE L ENG TO RESTART ON THE CTR TANK. IT DID NOT. I DECLARED AN EMER AND LANDED. AFTER THE LNDG AND TAXIING TO THE RAMP; I INSPECTED THE L ENG. THERE WAS NO OBVIOUS DAMAGE TO THE ENG. I STARTED THE ENG AND DID A THOROUGH RUN UP USING THE CTR TANK FOR THE FUEL SOURCE. THE ACFT WAS ALSO INSPECTED BY MECHS. THEY PUT FUEL IN THE AUX TANKS AND PERFORMED AT LEAST 2 VERY THOROUGH RUN-UPS USING BOTH ENGS AND BOTH THE MAIN AND AUX TANKS AS THE FUEL SOURCE. I SAW PART OF ONE RUNUP. I ESTIMATE THAT THEY RAN THE ACFT ON THE GND FOR AT LEAST 15 MINS AFTER I WALKED UP. AFTER THE GND RUNS; THE LINEMEN FILLED THE CTR TANK. THIS TANK TOOK 138.3 GALLONS OF FUEL TO FILL IT. THE CTR TANK HOLDS 156 GALLONS OF USABLE FUEL; SO THERE WAS 17.7 GALS OF FUEL IN THE TANK AFTER ALL THE RUN-UPS AND CHKS. I BELIEVE THAT WHEN I LANDED THERE WAS ADEQUATE FUEL ON BOARD TO MEET FAA MINIMUMS FOR IFR RESERVES. I USUALLY TRY TO HAVE MUCH MORE THAN MINIMUM FUEL ON BOARD. FOR THIS TRIP; IN ORDER TO HAUL ALL OF THE CARGO THE CUSTOMER WANTED TO SEND; I CHOSE TO GO WITH MINIMUM FUEL. I HAVE RELEARNED HOW IMPORTANT IT IS TO BE CONSERVATIVE IN IFR WX. IN RETROSPECT I COULD HAVE DONE SEVERAL THINGS TO MAKE THE FLT SAFER: 1) ASK THE CUSTOMER TO NOT PUT AS MUCH FREIGHT ON SO I COULD CARRY MORE FUEL. 2) ASK THE LINEMEN TO COME OUT AND FUEL THE ACFT AFTER HRS AT MY FIRST STOP. THERE WOULD HAVE BEEN A SMALL CHARGE AND POSSIBLY A DELAY. 3) WAIT FOR BETTER WX AT THE DEST. DEPENDING ON WHO DOES THE FUEL CALCULATIONS; IT MAY BE INFERRED THAT I DEPARTED WITHOUT ADEQUATE IFR FUEL RESERVES. IF I DID; IT WAS NOT FROM WILL INTENT.