Phil,
Do some research about what routes they fly and what type of aircraft they operate.
As an Ops Asst you'll be starting at the bottom, they'll need to appreciate you have no previous experience thus 'should' provide the necessary training.
Don't come across as a know it all, don't talk too much as if you are a 'reggy spotter', just come across as someone who is intelligent, prepared to learn and prepared to get your hands dirty. You need to get it across that you are flexible, able to work as a team player and whilst under pressure.
They'll probably expect you to relocate to live locally, before the interview go buy yourself the local newspaper(s) with all the ads in thus when they ask you about relocating you can say you've already started looking making a reference to the newspaper(s) in your bag.
If it is in Liverpool, good luck, you'll need it but good luck anyway.