There’s also evidence that the animals themselves may not fare so well. Riding on planes, being in closed-in spaces, and being exposed to loud noises and crowds of people can be overstimulating and scary to an animal, especially one not accustomed to that particular environment.
In a 2002 study, researchers looked at air travel in beagles. They found that blood and salivary cortisol was much higher than baseline in dogs during air transport, an indication they were stressed. The authors noted that just because the beagles were mainly inactive during transport did not mean they were not stressed. Rather, their behavior indicated that the beagles adopted a conservative-withdrawal approach in response to their stress, rather than fight-or-flight.
In contrast, service dogs are often genetically selected and extensively trained for the tasks they will perform. They need consistent and predictable behaviors in a wide range of situations and environments in order to safely provide service to their humans, especially if a life depends on that particular service.