No idea about CTC - or even aviation employers in general. But, aviation aside, failing a year at university won't be looked upon unfavourably by anyone, so long as there is a good reason for it.
Example: a very good friend of mine studied pharmacy at university. He failed his first year because he did could not get to grips with the dispensing side of the course (i.e. actually working in a high-street chemist). What he really wanted to do was pharmacology - the actual manufacturing of drugs. He started a more suitable course the next year, and no one viewed this negatively, because there was a good reason for it. (What they did view negatively was that he subsequently only just scraped through his new course, because he spent too much time drinking and sleeping!)
From reading your post, the only problem that I see is the line where you say: "If I were to fail a second time round". This is the wrong way to look at it. Your GCSE and A-Level results show that you are academically capable, so as long as you get yourself on the right course, there's no reason you should fail. Unless, of course, you go in with the attitude that you are going to fail, in which case you probably will.
FFF
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