I think Josh and Herc are right on the mark.

I can't imagine that many air carriers would retain an interest in a person who is willing to blow off an interview offer for other than a very good reason.

There are understandable reasons for turning down an interview. Hiring managers are well aware that you may not be able to make a short notice interview. Active crewmembers may have a problem getting released from their line, or maybe your only daughter's wedding is on that day.

Just remember that you sent them your resume. You asked them for a job. Asking to delay the interview (or the class date) without a reasonable explanation gives the distinct impression that you are not serious, or worse yet, that you're hoping for a better offer. No employer wants to be your "fall-back" option.