Not sure about a cheap polyester suit from ASDA - you're gonna look like a used car salesman! It wasn't green was it? Airline's want someone who is going to set an example and represent the company. And whilst variety inside an airline can be a good thing you can 'express yourself' once you've got a secure job so for the interview think conservative (with a small c)! Just make sure you look Professional (with a big P!) - grey / navy / dark suit, plain shirt with a brightish tie works for me. No tacky cufflinks, loud stripey shirts, mickey mouse ties / socks etc! And do the top button up - seems to be the latest thing to leave it undone!