R OUTBOARD FUEL CAP FALLS FROM LTT WHILE TAXIING FOR TKOF.

Narrative

WE WERE FUELED; APPROX 30 MINS PRIOR TO DEPARTING THE GATE. I LOADED THE PAX AND PERFORMED A WALKAROUND; LOOKING FOR ANY ABNORMALITIES SUCH AS FLAT TIRES; DAMAGED SURFACES; MISSING FUEL CAPS; ETC. I LOOKED AT EACH FUEL TANK (4) AND IT APPEARED ALL 4 CAPS WERE IN PLACE. I BOARDED THE ACFT; GAVE PAX BRIEFING AND PERFORMED BEFORE START CHKLIST. WE STARTED BOTH ENGS AND TAXIED FROM THE GATE. DURING THE TAXI CHK; MY FO CHKED THE R WING FOR CAPS; AND I CHKED L WING. DURING THE TAXI; THE R OUTBOARD CAP MUST HAVE FALLEN OFF AND ONTO THE TXWY. WE NEVER NOTICED A MISSING CAP AND FLEW BOS TO RKD AND RKD TO BHB. NO FUEL SIPHONED OUT DUE TO A FLAP INSIDE THE TANK. THE MORNING CREW FOUND THE MISSING R OUTBOARD CAP THE NEXT MORNING. THE CAP WAS FOUND ON THE RAMP IN BOS. I SURMISE THE FUELER DID NOT LOCK THE CAP DOWN AFTER PLACING IT ON THE TANK. BECAUSE IT WAS DARK AND THE WING WAS HIGHER; I COULD NOT TELL IT WAS NOT LOCKED DOWN. BECAUSE WE ALWAYS REGULARLY HAVE FUEL ORDERS WRONG (MORE OR LESS THAN WE ORDERED OR MORE IN ONE SIDE THAN THE OTHER) I ALWAYS CHK FOR FUEL CAPS IN FEAR THEY MIGHT FORGET THEM. FROM NOW ON I WILL HAVE TO CLB ON TOP OF WING OR UP A LADDER TO VERIFY THE CAP IS SECURE. I HAVE COMPLAINED SEVERAL TIMES ABOUT THE MISTAKES THAT COMMONLY OCCUR WITH OUR FUELERS. SO FAR; NO SIGNIFICANT CHANGE HAS OCCURRED.