Narrative:

We were between ZZZ1 and ZZZ2 on a delivery flight. The flight to ZZZ2 should have taken 3 hours and 50 mins based on a true airspeed of 125 KTS. With our wind calculations and fuel burn of about 9 gph; we should have had an endurance of 5 hours; and would have had more than IFR reserves left on board. At approximately 4 hours of flying time; I realized that we were running into our reserves so we asked ATC for a direct vector to ZZZ2 after declaring minimum fuel. Shortly after that; our left tank went dry and we switched over to our right tank which should have had at least 30 mins of fuel left. I then made a decision to divert to a closer airport (the closest hard-surfaced airport with fuel) 16 mi away. About 8 mi out; the engine sputtered and died and we declared an emergency. The engine came back to life and we continued to ZZZ3. The engine sputtered and revived itself 3 more times as we landed at ZZZ3. We made a safe landing and filled up the tanks. We had less than 1 gallon of fuel remaining. As it turned out; our airplane was burning closer to 11 gph and not 9 gph. The poh for the aircraft simply states fuel burn for percentage of power and not for a specific RPM. We believed we were burning fuel at 65%; when in fact it was probably more like 75% power. In addition; we might have been running the engine richer than supposed to because the cylinder head temperatures and oil temperatures were on the high side. The fuel gauges also read that we still had fuel after we had landed which was misleading (even though we are taught never to rely on the gauges). Had we picked another airport earlier; we would have saved ourselves the need to declare an emergency. However; if we had taken action any later; we probably would have had to land in a field. For the rest of the trip we added extra fuel stops.

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Original NASA ASRS Text

Title: GRUMMAN TIGER ON AN IFR FLT PLAN BURNS MORE FUEL THAN PLANNED. EMER DIVERSION TO A CLOSER ARPT WHILE EXPERIENCING INTERMITTENT ENG FAILURE DUE TO FUEL STARVATION.

Narrative: WE WERE BTWN ZZZ1 AND ZZZ2 ON A DELIVERY FLT. THE FLT TO ZZZ2 SHOULD HAVE TAKEN 3 HRS AND 50 MINS BASED ON A TRUE AIRSPD OF 125 KTS. WITH OUR WIND CALCULATIONS AND FUEL BURN OF ABOUT 9 GPH; WE SHOULD HAVE HAD AN ENDURANCE OF 5 HRS; AND WOULD HAVE HAD MORE THAN IFR RESERVES LEFT ON BOARD. AT APPROX 4 HRS OF FLYING TIME; I REALIZED THAT WE WERE RUNNING INTO OUR RESERVES SO WE ASKED ATC FOR A DIRECT VECTOR TO ZZZ2 AFTER DECLARING MINIMUM FUEL. SHORTLY AFTER THAT; OUR L TANK WENT DRY AND WE SWITCHED OVER TO OUR R TANK WHICH SHOULD HAVE HAD AT LEAST 30 MINS OF FUEL LEFT. I THEN MADE A DECISION TO DIVERT TO A CLOSER ARPT (THE CLOSEST HARD-SURFACED ARPT WITH FUEL) 16 MI AWAY. ABOUT 8 MI OUT; THE ENG SPUTTERED AND DIED AND WE DECLARED AN EMER. THE ENG CAME BACK TO LIFE AND WE CONTINUED TO ZZZ3. THE ENG SPUTTERED AND REVIVED ITSELF 3 MORE TIMES AS WE LANDED AT ZZZ3. WE MADE A SAFE LNDG AND FILLED UP THE TANKS. WE HAD LESS THAN 1 GALLON OF FUEL REMAINING. AS IT TURNED OUT; OUR AIRPLANE WAS BURNING CLOSER TO 11 GPH AND NOT 9 GPH. THE POH FOR THE ACFT SIMPLY STATES FUEL BURN FOR PERCENTAGE OF PWR AND NOT FOR A SPECIFIC RPM. WE BELIEVED WE WERE BURNING FUEL AT 65%; WHEN IN FACT IT WAS PROBABLY MORE LIKE 75% PWR. IN ADDITION; WE MIGHT HAVE BEEN RUNNING THE ENG RICHER THAN SUPPOSED TO BECAUSE THE CYLINDER HEAD TEMPS AND OIL TEMPS WERE ON THE HIGH SIDE. THE FUEL GAUGES ALSO READ THAT WE STILL HAD FUEL AFTER WE HAD LANDED WHICH WAS MISLEADING (EVEN THOUGH WE ARE TAUGHT NEVER TO RELY ON THE GAUGES). HAD WE PICKED ANOTHER ARPT EARLIER; WE WOULD HAVE SAVED OURSELVES THE NEED TO DECLARE AN EMER. HOWEVER; IF WE HAD TAKEN ACTION ANY LATER; WE PROBABLY WOULD HAVE HAD TO LAND IN A FIELD. FOR THE REST OF THE TRIP WE ADDED EXTRA FUEL STOPS.

Data retrieved from NASA's ASRS site as of January 2009 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.