Narrative:

Aircraft was en route ZZZ to ZZZ1. Filed route was 333 NM and approximately 1 hour 20 mins flight time. Aerostar tanks were filled at ZZZ 100 gallons loaded; approximately 150 gallons total on aircraft. Nominal endurance was 3 hours. Low fuel annunciation occurred approximately 1 hour 10 mins after departure; indicating 40 gallons fuel remaining. Visual fuel indication on 3 tanks (left wing; fuselage; right wing) showed substantially more fuel in right wing tank than left; and inconsistent with low fuel alert. PIC declared low fuel condition to ATC; and requested emergency rerte to nearest 5000 ft field (ZZZ2). ATC subsequently advised ZZZ2 notamed closed due to snow; and ATC then suggested ZZZ3. En route to ZZZ3; PIC reassessed fuel situation (including apparent increase in remaining fuel) and concluded adequate reserves existed for conclusion of flight to home base (ZZZ1). Aircraft proceeded ZZZ1 with no further difficulties. At time of low fuel annunciation; PIC assessed that apparent excessive fuel depletion rate was likely caused by unknown substantial fuel leak. This occurred following descent at 1500-2000 FPM descent from 17000 ft. Apparent erratic behavior of fuel gauge system and possible false low fuel annunciation caused by fuel loading imbal suggested critical fuel situation to PIC. On departure from ZZZ; a rudder trim problem on departure resulted in return to airport for examination. PIC determined that manual rudder trim had been inadvertently applied during taxi; instead of nosewheel steering; rudder trim and nosewheel steering rocker switches are adjacent on center console; with identical orientation. Safety cover on infrequently used rudder trim switch would have prevented this. An estimated 10 gallons of fuel was consumed during additional pattern circuits and taxiing to/from ramp. This would have reduced available flight time to about 2 hours 50 mins. Controled evaluation flight was taken following day round-robin ZZZ1-ZZZ4. Total block time was 1 hour 44 mins. Fuel flows (digital meter) were recorded in all flight stages. Calculated fuel burn was 61 gallons. Aircraft was fueled to 165 gallons prior to departure; and readings when back in hangar indicated 82 gallons; indicating 22 gallons of fuel unaccounted. Further analysis and examination of fuel gauge system will be undertaken. Callback conversation with reporter revealed the following information: reporter stated he was informed by more experienced mechanics the fuel gauges were fine; but; the aerostar does have a very sensitive wing fuel balance system. Any imbalance in the wing tanks; such as one wing fuller than the other; tends to initiate fuel warning annunciation. Reporter also stated he has been flying the aerostar for only six months.

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Original NASA ASRS Text

Title: AN AEROSTAR PA-61 PILOT REPORTS OF LOW FUEL ANNUNCIATION AND REQUESTED EMERGENCY REROUTE TO NEAREST 5000 FT FIELD.

Narrative: ACFT WAS ENRTE ZZZ TO ZZZ1. FILED RTE WAS 333 NM AND APPROX 1 HR 20 MINS FLT TIME. AEROSTAR TANKS WERE FILLED AT ZZZ 100 GALLONS LOADED; APPROX 150 GALLONS TOTAL ON ACFT. NOMINAL ENDURANCE WAS 3 HRS. LOW FUEL ANNUNCIATION OCCURRED APPROX 1 HR 10 MINS AFTER DEP; INDICATING 40 GALLONS FUEL REMAINING. VISUAL FUEL INDICATION ON 3 TANKS (L WING; FUSELAGE; R WING) SHOWED SUBSTANTIALLY MORE FUEL IN R WING TANK THAN L; AND INCONSISTENT WITH LOW FUEL ALERT. PIC DECLARED LOW FUEL CONDITION TO ATC; AND REQUESTED EMER RERTE TO NEAREST 5000 FT FIELD (ZZZ2). ATC SUBSEQUENTLY ADVISED ZZZ2 NOTAMED CLOSED DUE TO SNOW; AND ATC THEN SUGGESTED ZZZ3. ENRTE TO ZZZ3; PIC REASSESSED FUEL SITUATION (INCLUDING APPARENT INCREASE IN REMAINING FUEL) AND CONCLUDED ADEQUATE RESERVES EXISTED FOR CONCLUSION OF FLT TO HOME BASE (ZZZ1). ACFT PROCEEDED ZZZ1 WITH NO FURTHER DIFFICULTIES. AT TIME OF LOW FUEL ANNUNCIATION; PIC ASSESSED THAT APPARENT EXCESSIVE FUEL DEPLETION RATE WAS LIKELY CAUSED BY UNKNOWN SUBSTANTIAL FUEL LEAK. THIS OCCURRED FOLLOWING DSCNT AT 1500-2000 FPM DSCNT FROM 17000 FT. APPARENT ERRATIC BEHAVIOR OF FUEL GAUGE SYS AND POSSIBLE FALSE LOW FUEL ANNUNCIATION CAUSED BY FUEL LOADING IMBAL SUGGESTED CRITICAL FUEL SITUATION TO PIC. ON DEP FROM ZZZ; A RUDDER TRIM PROB ON DEP RESULTED IN RETURN TO ARPT FOR EXAM. PIC DETERMINED THAT MANUAL RUDDER TRIM HAD BEEN INADVERTENTLY APPLIED DURING TAXI; INSTEAD OF NOSEWHEEL STEERING; RUDDER TRIM AND NOSEWHEEL STEERING ROCKER SWITCHES ARE ADJACENT ON CTR CONSOLE; WITH IDENTICAL ORIENTATION. SAFETY COVER ON INFREQUENTLY USED RUDDER TRIM SWITCH WOULD HAVE PREVENTED THIS. AN ESTIMATED 10 GALLONS OF FUEL WAS CONSUMED DURING ADDITIONAL PATTERN CIRCUITS AND TAXIING TO/FROM RAMP. THIS WOULD HAVE REDUCED AVAILABLE FLT TIME TO ABOUT 2 HRS 50 MINS. CTLED EVALUATION FLT WAS TAKEN FOLLOWING DAY ROUND-ROBIN ZZZ1-ZZZ4. TOTAL BLOCK TIME WAS 1 HR 44 MINS. FUEL FLOWS (DIGITAL METER) WERE RECORDED IN ALL FLT STAGES. CALCULATED FUEL BURN WAS 61 GALLONS. ACFT WAS FUELED TO 165 GALLONS PRIOR TO DEP; AND READINGS WHEN BACK IN HANGAR INDICATED 82 GALLONS; INDICATING 22 GALLONS OF FUEL UNACCOUNTED. FURTHER ANALYSIS AND EXAM OF FUEL GAUGE SYS WILL BE UNDERTAKEN. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: REPORTER STATED HE WAS INFORMED BY MORE EXPERIENCED MECHANICS THE FUEL GAUGES WERE FINE; BUT; THE AEROSTAR DOES HAVE A VERY SENSITIVE WING FUEL BALANCE SYSTEM. ANY IMBALANCE IN THE WING TANKS; SUCH AS ONE WING FULLER THAN THE OTHER; TENDS TO INITIATE FUEL WARNING ANNUNCIATION. REPORTER ALSO STATED HE HAS BEEN FLYING THE AEROSTAR FOR ONLY SIX MONTHS.

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.