This means each airline has its own rules about what animals can fly in the cabin, usually for a fee of $95 to $120, and the specific dimensions of the carriers (which can even vary by aircraft). Furthermore, some prohibit certain breeds of dogs, where others allow any dog, cat, household bird or other critter that fits weight restrictions, most commonly a 20-pound-plus-carrier weight limitation that is strictly enforced and can lead to last minute treat-restriction. Spirit has a 40-pound limit and allows household birds, raising some intriguing questions about pet turkeys I don’t have time to get into here.
But the language on how to tell whether a pet fits into its carrier is generally the same, probably because it’s the one area where both the government and the International Air Transport Association, or IATA, an international trade association, have weighed in. Federal regulations state animals must have “enough space to turn about normally while standing, to stand and sit erect, and to lie in a natural position,” and IATA’s guidelines are quite similar.
I contacted both United, for your case, and American, for Betsy’s, and got two completely different answers.
United requires that pets be able to “stand up and turn around while inside.” But what that means is subject to some interpretation. “In order to be accepted,” Erin Jankowski, a United spokeswoman, wrote to me in an email, “a pet must be able to stand up and turn around without rocking or tipping over the carrier.”
I followed up, sending along your complaint in full. The answer was short on specifics, but direct. “In this particular case,” she responded, “the agent made the correct decision based on our guidelines.” She added that you received a refund within days for the original cost of your flight, but did not address why Bella had been allowed on previous flights.