I have flown with my dog in the large Sherpa for the past 11 years. He's flown on United, Air Tran, Southwest, American and Jet Blue for a total of about 40 times. He is 20 pounds but has short legs. He has plenty of room (it's all relative, right?) in the bag and can easily turn around. I have never, not once, been hassled by flight attendants or gate agents about the size of the bag or the weight of of my dog. I *do* have to squish the bag down sometimes, but really, my dog is fine. Is he comfortable? Probably not. But it beats he hell out of checking him, which I simply will not do.