I use the Motherlode Mini 21" carry on ( 21.5" x 15" x 9" ) on my trips. I have a trip coming up where I start on United and the bag is fine, although I have a connection where I transfer to Air Dolomiti. I checked and their carry on size limit is 21.65 x 15.74 x 7.8, and a weight limit of 15.4 pounds. I am guessing they will just check my bag at the gate? Will there be a charge to check at the gate?