Did you look through the stickies and read the one on the Amended Air Carrier Access Act? It may help answer some of your questions.
As you can see there are additional requirements when traveling with a PSD. In this way they are linked in with ESAs.
#41. For purposes of providing documentation stating a passenger’s disability-related need for an emotional support or psychiatric service animal1, what kind of practitioners qualify as “licensed mental health professionals”?
Answer: Any licensed mental health professional (e.g., psychiatrist, psychologist, licensed clinical social worker) including a medical doctor who is specifically treating a passenger’s mental or emotional disability is a practitioner qualified to provide documentation stating the passenger’s need for an emotional support or psychiatric service animal. A qualified practitioner would include a general practitioner who is treating the passenger’s mental or emotional disability.
#42. May a carrier require that the documentation a passenger provides in order to travel with an animal that is used as an emotional support or psychiatric service animal state the passenger’s specific mental or emotional condition?
Answer: No. A carrier may only require that a passenger’s documentation confirm that a passenger has a mental or emotional disability recognized in the Diagnostic and Statistical Manual of Mental Disorders- Fourth Edition (DSM-IV), in addition to three other items (i.e., the passenger needs the animal for air travel and/or activity at the passenger’s destination, the individual providing the assessment is a licensed mental health professional and that passenger is under his/her care, the date and type of mental health professional’s license and the state or other jurisdiction in which it was issued).
#43. May a carrier accept documentation from a licensed mental health professional concerning a passenger’s need for a psychiatric or emotional support animal if the documentation is more than one year old?
Answer: Carriers may, at their discretion, accept from the passenger with a disability documentation from his or her licensed mental health professional that is more than one year old. We encourage carriers to consider accepting “outdated” documentation in situations where such passenger provides a letter or notice of cancellation or other written communication indicating the cessation of health insurance coverage, and his/her inability to afford treatment for his or her mental or emotional disability.