Is a psychologist part of every accident investigation team?
Well, in most "first world" (and I certainly use that term loosely) investigations the answer is that
access to a psychologist is a planned part of the "on scene" portions of an investigation. And also for some of the subsequent activities. For example, as you might imagine, actual voice recordings can be most traumatic to listen to.
Clearly, in this case
access to a psychologist means that the person must be onboard the ship.