I applied last year and got through to stage 3. Flybe had 4 places, not sure how many this year.
Stage 1 is the application, stage 2 is the tests. The maths and physics tests are fairly simple, mainly GCSE level sometimes slightly higher but fairly simple and are multiple choice. You cant train really for the pilapt tests, the whole point is you can either do them or not. They consist of lots of little tasks, aimed to see how you pick things up, learn from mistakes etc. There isnt a true pass or fail on this, as it will just depend on how well everyone else does and if your in the top group.
Stage 3 will be the final 16 people and is a group exercise, debate, followed by a single interview.
stage 4 is the final 8 people and is with flybe. As far as i know this is just an interview with them and thats it.