just because an ATCO may not be present at an interview doesn't mean that they have not been involved. i have been told that ATCO's across the whole of the compnay in both disciplines were used to design the new competancy based interview.
the best advice to prepare for any interview is think of good work & personal examples that can be adapted to the Q's being asked of you. i rang HR for advice on what to expect and they were very helpful - make sure that you are speaking to someone in the TATC recruitment team for the correct advice though.
i agree with a previous post that you should remember that this is a RUMOUR network and not to take everything you read as the truth. if you are in any doubt speak to the professionals. i always contacted them by replying to the "invite/confirmation" emails and they always got back to me within 2 days.