Narrative:

This was leg #4 of a 12 hour day, a ferry to set up for the following day. I ordered and paid for the fuel and the trip to ZZZ1 departed uneventfully. During the flight, the fuel quantity seemed low. We checked the FMS and it showed more fuel than the gauges. We reset the current fuel quantity on the FMS and the landing computation was lower than planned. It was, however, still above company landing minimums. The WX at ZZZ1 was good VFR with no alternate. We throttled back on the power and remained at high altitude as long as possible to conserve fuel. In descent and 50 mi from ZZZ1, the FMS was still showing adequate fuel supply at destination, but the gauges were indicating landing fuel quantity 50 mi out. Now not sure exactly how much fuel we would have upon landing and anticipating possible delays in the area we diverted to ZZZ2, stated to the controller we were unsure of the fuel quantity, and requested a precautionary landing at the nearest suitable airport. The approach controller declared an emergency though not required. The landing at ZZZ2 was uneventful and we landed above company minimums. After landing, emergency equipment arrived and since not required, departed quickly. After checking the logbook, I realized I did not order sufficient fuel for the trip due to my mathematical error. I also did not catch the error before our departure. Though we attempted to complete the mission in a safe manner, when that was in question, we took the safest course of action and diverted. Adherence to checklists and SOP's would have averted this situation.

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Original NASA ASRS Text

Title: A C560 PLT MISCALCULATED HIS TRIP FUEL REQUIREMENT AND AS A PRECAUTION LANDED SHORT OF THE DEST AFTER SUSPECTING A FUEL REMAINING ERROR.

Narrative: THIS WAS LEG #4 OF A 12 HR DAY, A FERRY TO SET UP FOR THE FOLLOWING DAY. I ORDERED AND PAID FOR THE FUEL AND THE TRIP TO ZZZ1 DEPARTED UNEVENTFULLY. DURING THE FLT, THE FUEL QUANTITY SEEMED LOW. WE CHKED THE FMS AND IT SHOWED MORE FUEL THAN THE GAUGES. WE RESET THE CURRENT FUEL QUANTITY ON THE FMS AND THE LNDG COMPUTATION WAS LOWER THAN PLANNED. IT WAS, HOWEVER, STILL ABOVE COMPANY LNDG MINIMUMS. THE WX AT ZZZ1 WAS GOOD VFR WITH NO ALTERNATE. WE THROTTLED BACK ON THE PWR AND REMAINED AT HIGH ALT AS LONG AS POSSIBLE TO CONSERVE FUEL. IN DSCNT AND 50 MI FROM ZZZ1, THE FMS WAS STILL SHOWING ADEQUATE FUEL SUPPLY AT DEST, BUT THE GAUGES WERE INDICATING LNDG FUEL QUANTITY 50 MI OUT. NOW NOT SURE EXACTLY HOW MUCH FUEL WE WOULD HAVE UPON LNDG AND ANTICIPATING POSSIBLE DELAYS IN THE AREA WE DIVERTED TO ZZZ2, STATED TO THE CTLR WE WERE UNSURE OF THE FUEL QUANTITY, AND REQUESTED A PRECAUTIONARY LNDG AT THE NEAREST SUITABLE ARPT. THE APCH CTLR DECLARED AN EMER THOUGH NOT REQUIRED. THE LNDG AT ZZZ2 WAS UNEVENTFUL AND WE LANDED ABOVE COMPANY MINIMUMS. AFTER LNDG, EMER EQUIP ARRIVED AND SINCE NOT REQUIRED, DEPARTED QUICKLY. AFTER CHKING THE LOGBOOK, I REALIZED I DID NOT ORDER SUFFICIENT FUEL FOR THE TRIP DUE TO MY MATHEMATICAL ERROR. I ALSO DID NOT CATCH THE ERROR BEFORE OUR DEP. THOUGH WE ATTEMPTED TO COMPLETE THE MISSION IN A SAFE MANNER, WHEN THAT WAS IN QUESTION, WE TOOK THE SAFEST COURSE OF ACTION AND DIVERTED. ADHERENCE TO CHKLISTS AND SOP'S WOULD HAVE AVERTED THIS SIT.

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.