you can be hired part time, or at least you could when i worked there.
heres one other thing i forgot to mention, again this is how it was at amr northeast div almost 4 years ago. it might not be national policy:
during orientation, you sit down with the scheduler and pick your shift from the list of available shifts. you then sign a contract agreeing to work that shift for 9 months before you can change it. get into nursing school, tough crap. wife has a baby, oh well. they did have a few outs for you. if they created a brand new shift, you could bid on that at any time. you could also change your status(ft>pt) you could be released. thats about it. this goes back to them not caring about you as a person. things change in peoples lives and a company that cares about its employees understands that. a company that isnt concerned with their employees institutes a policy that makes it easier on the scheduling dept, but can be devastating for the employee.