查了一下: AA: http://www.aa.com/i18n/travelInformation/specialAssistance/trav The maximum size for cabin pet carriers is 19" long x 13" wide x 9" high. Soft-sided pet carriers such as Sherpa bags may exceed these dimensions slightly because they are collapsible. Animals must be able to stand up, turn around and lie down in a natural position in the kennel. Soft-sided pet carriers are accepted as long as they are constructed of water-repellent, padded nylon with mesh ventilation on two or more sides. JetBLue: http://help.jetblue.com/SRVS/CGI-BIN/webisapi.dll?New,Kb=askBlu A carrier that does not exceed 17"L (43.18 cm) x 12.5"W (31.75 cm) x 8.5"H (21.59 cm). Your pet must be able to stand up and move around in the carrier with easeCombined weight of your pet and carrier may not exceed 20 pounds Carriers must have a leak proof bottom and must be well ventilated Soft- sided and hard-sided carriers are acceptable Only one pet per carrier is allowed UA: http://www.united.com/web/en-US/content/travel/animals/in_cabin In-cabin pet kennels A pet traveling in cabin must be carried in an approved hard-sided or soft- sided kennel. The kennel must fit completely under the seat in front of the customer and remain there at all times. The maximum dimensions for hard- sided kennels are 17.5 inches long x 12 inches wide x 7.5 inches high (44 cm x 30 cm x 19 cm). The maximum dimensions for soft-sided kennels are 18 inches long x 11 inches wide x 11 inches high (46 cm x 28 cm x 28 cm). There may only be one cat or dog per kennel, and the animal must be able to stand up and turn around comfortably.