Suitability for flying
A veterinarian cannot certify that an animal is healthy and fit for any purpose (including flights) because there are too many unknowns. To try to do so places the veterinarian in the realm of the psychic, which is far beyond any mere mortal veterinarian’s capabilities. We could not possibly be aware of all the stressors that may be present in animal transportation by aeroplane or how any individual may respond. We are not placing your dog or cat on the plane nor are we flying the plane so it is impossble for us to certify that an animal is suitable for any stressors such as flying that is unknown to your pet or us.
Although airlines may request veterinary certification they also allow all owners to sign a waiver for transport that the owner acknowledges and accepts the risk of transport.