Flight Crew Air Transport Pilot (ATP)
Other / Unknown
Deviation / Discrepancy - Procedural FAR; Deviation / Discrepancy - Procedural Published Material / Policy; Deviation / Discrepancy - Procedural Weight And Balance; Inflight Event / Encounter Fuel Issue
General None Reported / Taken
Human Factors
We took off with 4;000 LBS of fuel when our dispatch release and weight and balance was calculated at 3;000 LBS of fuel. So our numbers for weight and balance fuel load was severely incorrect. We were not overweight for takeoff even with this error. We still had about 600 LBS under the maximum gross takeoff weight of 17;120 LBS. I was not aware that there was 1;000 LBS of fuel in the auxiliary tanks. For some reason I did not hit the switch during prefight or before taxi. I usually will check for sure both main and auxiliary fuel gauges on the before taxi checklist; but for some reason I did not. I discovered this in flight when I happen to check to see if anything was still in the auxiliary tanks. I turned on the auxiliary pumps to see if there was anything and there was no master caution for them and no drain on the main tanks. I advised arrival operations to start finding 5 passengers to volunteer to take another flight to insure we have good weight and balance for the next flight. I also had them call Dispatch to see if they want us to hold over the airport for sometime to burn the excess fuel; but they advised not to and call them on ground. I did burn up all the fuel in the auxiliary tank before landing. This aircraft just came from two test flights. How did both crews before this flight find out that there was fuel in the auxiliary tank? The logbook fuel gallons did not reflect fuel in the auxiliary tanks only the mains. They both must have not check the auxiliary tank too. I did overhear a conversation to a dispatcher of the fuel load in the aircraft before today's test flight before mine of the fuel load and they seamed to be only aware of what the fuel load was in the mains. The fuel receipt that I got from the fuelers did reflect only adding fuel to the mains. I will not make this mistake of not checking the auxiliary tank fuel gauges again. The only thing I can think of to eliminate the problem is to reduce the checklist to separate each tank in a new line and not one. So instead of fuel total Main; Auxiliary. It could be total fuel main tanks; then total fuel auxiliary tanks on two separate lines.
[Narrative 2 had no additional information.]
Beech 1900 flight crew operated aircraft unaware of 1;000 LBS of additional fuel in the auxiliary fuel tanks.