Narrative:

I departed oak on a night cargo flight to bur. I was flying a PA31 for an far 135 operator. I departed on the VFR flight with what I thought was 700-800 pounds of fuel. This is enough to reach my destination with over 1 hour reserve. When reaching cruise flight, I began my fuel management and discovered that my outboard tanks did not have the amount of fuel that I thought. At this time I researched the performance section to see if I would have enough fuel to complete the flight with minimum reserve fuel. I also was picking a suitable airport to land and pick up fuel to complete the flight in case I did not have the fuel required. I made error in interping the fuel gauges. My inboard gauges read a little over 1/4 on each main tank and in the weight and balance section showed that a 1/4 tank is about 26 gallons. In my interpretation I attributed the 26 gallons to both main fuel gauges and came up with a total of 52 gallons in the main tank. In reality, there were only 26 gallons total in the main tanks. I reduced my power setting to a fuel flow of less than 20 gph total and proceeded on to my destination thinking I had 2 hours of fuel (52 gallons) for my 1 hour remaining flight. Ground fog was forming between me and my destination. When I realized that my fuel gauges were decreasing at a rate twice that I had anticipated I was at a point where my only safe option was to continue to my destination area where there was VFR conditions on the ground. I realized my error too late and was faced with reaching my destination without any remaining reserve fuel. When realizing the full gravity of my situation I told approach that I needed to land immediately at the closest suitable airport. I landed at vny without incident. In hindsight, I can see many factors which contributed to my making such a primary error. 1) working on the back side of the clock seems to avail itself to more errors than working during the day. 2) single pilot unpressurized aircraft at night at 9500 ft can cause a decrease in mental acuity. 3) stress induced by company schedule and repercussions for delays and errors. 4) having 2 main fuel gauges which don't read gallons or pounds but amount full, such as F, east, and indicators in between. So, when I referred to the weight and balance section and saw that 1/4 meant 26 gallons, I added each 1/4 tank and came up with 52 gallons. 5) I have only flown this model aircraft 4 times in the last yr and all the other aircraft I fly have fuel gauges that give indications of pounds of fuel remaining per tank. While back on the ground, I see the simplicity of my error and can hardly believe that this could happen to me. I have searched within me to discover the human factors which affect the decision making process. Of course I take full responsibility for all my actions.

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Original NASA ASRS Text

Title: PLT OF PA31 AIR TAXI CARGO ACFT MISREADS AND MISCALCULATES THE FUEL QUANTITY. WITH LOW FUEL CONDITION HE DIVERTS.

Narrative: I DEPARTED OAK ON A NIGHT CARGO FLT TO BUR. I WAS FLYING A PA31 FOR AN FAR 135 OPERATOR. I DEPARTED ON THE VFR FLT WITH WHAT I THOUGHT WAS 700-800 LBS OF FUEL. THIS IS ENOUGH TO REACH MY DEST WITH OVER 1 HR RESERVE. WHEN REACHING CRUISE FLT, I BEGAN MY FUEL MGMNT AND DISCOVERED THAT MY OUTBOARD TANKS DID NOT HAVE THE AMOUNT OF FUEL THAT I THOUGHT. AT THIS TIME I RESEARCHED THE PERFORMANCE SECTION TO SEE IF I WOULD HAVE ENOUGH FUEL TO COMPLETE THE FLT WITH MINIMUM RESERVE FUEL. I ALSO WAS PICKING A SUITABLE ARPT TO LAND AND PICK UP FUEL TO COMPLETE THE FLT IN CASE I DID NOT HAVE THE FUEL REQUIRED. I MADE ERROR IN INTERPING THE FUEL GAUGES. MY INBOARD GAUGES READ A LITTLE OVER 1/4 ON EACH MAIN TANK AND IN THE WT AND BAL SECTION SHOWED THAT A 1/4 TANK IS ABOUT 26 GALLONS. IN MY INTERP I ATTRIBUTED THE 26 GALLONS TO BOTH MAIN FUEL GAUGES AND CAME UP WITH A TOTAL OF 52 GALLONS IN THE MAIN TANK. IN REALITY, THERE WERE ONLY 26 GALLONS TOTAL IN THE MAIN TANKS. I REDUCED MY PWR SETTING TO A FUEL FLOW OF LESS THAN 20 GPH TOTAL AND PROCEEDED ON TO MY DEST THINKING I HAD 2 HRS OF FUEL (52 GALLONS) FOR MY 1 HR REMAINING FLT. GND FOG WAS FORMING BTWN ME AND MY DEST. WHEN I REALIZED THAT MY FUEL GAUGES WERE DECREASING AT A RATE TWICE THAT I HAD ANTICIPATED I WAS AT A POINT WHERE MY ONLY SAFE OPTION WAS TO CONTINUE TO MY DEST AREA WHERE THERE WAS VFR CONDITIONS ON THE GND. I REALIZED MY ERROR TOO LATE AND WAS FACED WITH REACHING MY DEST WITHOUT ANY REMAINING RESERVE FUEL. WHEN REALIZING THE FULL GRAVITY OF MY SIT I TOLD APCH THAT I NEEDED TO LAND IMMEDIATELY AT THE CLOSEST SUITABLE ARPT. I LANDED AT VNY WITHOUT INCIDENT. IN HINDSIGHT, I CAN SEE MANY FACTORS WHICH CONTRIBUTED TO MY MAKING SUCH A PRIMARY ERROR. 1) WORKING ON THE BACK SIDE OF THE CLOCK SEEMS TO AVAIL ITSELF TO MORE ERRORS THAN WORKING DURING THE DAY. 2) SINGLE PLT UNPRESSURIZED ACFT AT NIGHT AT 9500 FT CAN CAUSE A DECREASE IN MENTAL ACUITY. 3) STRESS INDUCED BY COMPANY SCHEDULE AND REPERCUSSIONS FOR DELAYS AND ERRORS. 4) HAVING 2 MAIN FUEL GAUGES WHICH DON'T READ GALLONS OR LBS BUT AMOUNT FULL, SUCH AS F, E, AND INDICATORS IN BTWN. SO, WHEN I REFERRED TO THE WT AND BAL SECTION AND SAW THAT 1/4 MEANT 26 GALLONS, I ADDED EACH 1/4 TANK AND CAME UP WITH 52 GALLONS. 5) I HAVE ONLY FLOWN THIS MODEL ACFT 4 TIMES IN THE LAST YR AND ALL THE OTHER ACFT I FLY HAVE FUEL GAUGES THAT GIVE INDICATIONS OF LBS OF FUEL REMAINING PER TANK. WHILE BACK ON THE GND, I SEE THE SIMPLICITY OF MY ERROR AND CAN HARDLY BELIEVE THAT THIS COULD HAPPEN TO ME. I HAVE SEARCHED WITHIN ME TO DISCOVER THE HUMAN FACTORS WHICH AFFECT THE DECISION MAKING PROCESS. OF COURSE I TAKE FULL RESPONSIBILITY FOR ALL MY ACTIONS.

Data retrieved from NASA's ASRS site as of July 2007 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.