Kip_smyth, the thing about those cabin crew diploma courses is that they dont actually guarantee you a job. No-one in my company has done a course. at the end of the day, airlines are going to hire the person with the best personality, customer service experience etc than the person who has done an airline course.
Im glad youve decided to apply for airlines though, thats fantastic! Its great that you are preparing yourself for some knock-backs too...so many people give up after their first knock-back. just stay positive! And you never know, this time could be it!
Goodluck x