SA-227 AC Metro III
Flight Crew Commercial
Situational Awareness
Aircraft Equipment Problem Critical; Inflight Event / Encounter Fuel Issue
General Maintenance Action
Human Factors; Aircraft
During preflight of the aircraft; I noted that the fuel quantity indicators showed 2;300 lbs. of fuel after the system test. The needles were more sluggish and jittery than normal in their movement from the test position to the fuel quantity indication; so I elected to verify the quantity with the magnastick in each wing. Upon inspection of the magnastick I found the left-wing indicated between 150 and 155 gallons of fuel equivalent to approximately 1100 pounds of fuel. I found the right-wing not to indicate clearly; but the float-magnet seemed to be pulling the stick into the wing fully; so I assumed the quantity matched with the cockpit indicator with approximately 1;200 lbs. in that wing. This total was sufficient to complete the run; so; I did not order any further fuel. The first leg continued normally to the destination. Upon landing the fuel quantity indicator appeared to have stuck during flight and so I used the test function again and compared the new indication after the test with the fuel totalizer and previous fuel figures to agree with 500 lbs burned and 1800 lbs remaining. After unloading cargo and preparing for the return leg I did not feel the need to inspect the magnasticks to verify the fuel quantity as both methods had agreed at the start of the day and the cockpit indicator was still indicating expected values. Engine start and departure were completed with no abnormal indications. Reaching cruise I noted the fuel quantity guage read 900 lbs in the left tank and 1;100 lbs. in the right tank; a number which could not have been correct. I attempted to use the test function again but the needles returned to their original 900 and 1100 positions. As the totalizer was still functioning and I had departed with what appeared to be adequate fuel for the flight and approximately 1:30 minutes of reserve I elected to continue. During descent to landing I observed the L XFlow annunciator illuminate and applied the memory item of switching to the opposite (from main to standby on an odd numbered day) pump and noted that during the flight my knee had moved the switch to the off position. The annunciator promptly extinguished. Landing was accomplished normally. During postflight; I noted a fuel burn of 700 lbs approximately [but] was unable to determine fuel remaining from the cockpit quantity gauge and attempted to use the magnasticks. Both sticks dropped to full travel and would not catch on the float magnet at any point leaving me unable to verify fuel quantity remaining. The discrepancy was noted in the AML and chief pilot on call notified as a precaution due to the unknown fuel quantity on landing. After returning the AML to the maintenance office I located the previous day's runsheet and noted the fuel remaining as 1200 pounds; within 150 pounds of my total burn for the day and 1100 pounds different from the fuel indicated by both the quantity gauge and magnasticks.I became aware of the event when attempting to determine the fuel quantity on board during aircraft postflight and noted the critical situation after determining the actual fuel on-board from the previous day's paperwork.Dual failure of both fuel quantity indicating systems combined with a failure to confirm previous fuel onboard and complacency with using one the cockpit indicating system when both appeared to be working at the start of the day.I notified the Chief Pilot; made an entry in the logbook; and confirmed with the pilot supervisor that no fuel was known to be added to the aircraft.Further verification of fuel onboard the aircraft through continuous logs in the AML to verify each day when and how much fuel was added and burned; along with an increase in the use and inspection of the magnastick system.
SA227 Captain reported dual failure of the fuel quantity gauges and resulting operation of the aircraft with less fuel than planned.