SAAB 340B WAS OPERATED WITH THE COCKPIT L FUEL QUANTITY INDICATOR AND L FUELING PANEL INDICATOR INOP PER THE MEL. WITH THIS COMBINATION FUEL DIPSTICKS CANNOT BE USED FOR FUELING.

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ON MAY/SUN/06; MY FLTS XXX AND YYY A ROUND-TRIP FROM ZZZ TO ZZZ1; HAD MEL'S 28-09 AND 28-10. THERE WAS SOME CONFUSION AS TO HOW TO COMPLY WITH THE LIMITATIONS OF THE MEL'S. I SPOKE WITH THE CAPT; AND OVER ABOUT 20 MINS; 2 PHONE CALLS; AND A CONFERENCE WITH MAINT CTL; WE DETERMINED THAT WE COULD OPERATE THE FLT WHILE SATISFYING THE LIMITATIONS OF THE MEL'S. UPON READING THE PROCS FOR MEL 28-10; HOWEVER; THE CAPT AND I MISSED OR MISINTERPED THE RESTR OF USING THE COCKPIT FUEL QUANTITY GAUGES ONLY FOR DETERMINING FUEL QUANTITY. UPON FURTHER REVIEW; IT APPEARS THAT BOTH MEL'S REFED THE L SYS AND; THEREFORE; 28-10 COULD NOT BE COMPLIED WITH. I BELIEVE WE BOTH (AND MAINT CTL) MISSED THE COCKPIT GAUGE PROC FROM 28-10; AND UNKNOWINGLY VIOLATED THAT PROVISION OF THE MEL. IT IS POSSIBLE THAT WE FIXATED ON STICKING THE TANKS AS A SOLUTION; AS IT WAS AN OPTION FOR 28-09; AND DIDN'T CATCH THE FACT THAT THE STICKING PROC WAS NOT ALLOWED FOR 28-10. ANOTHER POSSIBILITY WAS THAT WE KNEW THAT THE COCKPIT GAUGES WERE REQUIRED FOR 28-10; BUT SINCE 28-09 HAD AN ALTERNATE MEANS OF DETERMINING FUEL QUANTITY (THE APPROVED STICKING PROC); THAT WE 'TALKED OURSELVES INTO' BEING ABLE TO USE THE STICKING PROC TO SATISFY 28-10 AS WELL AS 28-09. CONTRIBUTING FACTORS WERE THE FACT THAT BOTH MEL'S HAD BEEN PREVIOUSLY FLOWN; LEADING US TO BELIEVE THAT THERE MUST BE A WAY OTHERS WERE DOING IT. ALSO; THESE 2 MEL'S CAN BE COMBINED IN THE OTHER ACFT TYPES; AND PERHAPS THAT CLOUDED OUR JUDGEMENT. IN THE END THOUGH; WE OBVIOUSLY ERRED IN REGARDS TO THE LIMITATIONS OF 28-10; BUT BELIEVED AT THE TIME THAT WE HAD SATISFIED THE REQUIREMENTS OF THE MEL'S. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE RPTR STATED THIS SIT OF COCKPIT INDICATOR AND UNDERWING INDICATOR INOP ON THE SAME TANK PROHIBITS THE USE OF DIPSTICKS. THE MEL READS FOR THE UNDERWING INDICATOR IF INOP TO USE THE COCKPIT INDICATOR FOR FUELING BUT PROHIBITS THE USE OF THE TANK DIPSTICKS FOR FUEL QUANTITY CHKS. IN THIS SIT THE COCKPIT INDICATOR WAS ALSO INOP AND USE OF THE TANK DIPSTICKS WAS PROHIBITED. THE MANUFACTURER'S MEL DOES NOT HAVE THIS LIMIT AND DIPSTICK USE IS ALLOWED.