H) Animals Other than Service Animals ... UA will accept domesticated cats, dogs, rabbits and household birds for transportation as in-cabin Baggage for domestic carriage and travel between U.S.A./Canada and Mexico, the Caribbean, Central and South America....UA will not accept dogs of the Pit Bull breed,
1) General Conditions of Acceptance
a) Advance arrangements must be made. Space must be reserved for animals in either the passenger or cargo compartment. Animals without reserved space will be accepted, if space is available, only after the animals for whom space has been reserved have been accommodated.
b) The animal must be harmless, inoffensive, odorless and require no attention during transit.
c) The animal must be confined in a cage or container subject to inspection and approval by UA before acceptance and must meet the department of agriculture requirements prior to acceptance.
d) The container must be stored under the seat directly in front of the Passenger at all times, and the animal must remain in the container at all times.
.

g) There may be only one cat or dog per container, and the animal must be able to stand up and turn around comfortably.

NOTE: Animals will not be accepted for carriage on some United Express flights.
2) Pet Containers
a) Containers must be leak-proof and subject to inspection and approval by UA prior to acceptance.
b) Containers must be made of metal, wood, polyethylene, fiberglass or composite material of similar strength.
c) Containers must be ventilated on at least two sides and prevent any part of the animal from protruding outside of the container.
d) Containers made totally of wire are not accepted.
e) Approved soft side carriers specifically designed as pet carriers are acceptable.

f) In-cabin animal containers must not exceed 17.5 inches in length by 12 inches in width by 7.5 inches in height for hard sided containers and 18 inches in length by 11 inches in width by 11 inches in height for soft sided containers.
....