OCL, I attended them last year.
In short, they are maths, maths and more maths.
A lot of trigonometry, 3:4:5 triangles, etc.
All the kind of stuff I learnt at GCSE / A-Level, but have not used and therefore forgotten in the 8 years since leaving school!
There is also an aural exercise where the tutor reads out information, and you have to cross check it against graphs and charts - take-off distances, landing weights, etc.
And finally a mechanical aptitude test, with lots of diagrams of wheels and pullies, etc - i.e. if cog A turns in one direction, cog B in another, what direction will cog C turn? That kind of thing. I found this the easiest, but I found that the people who aced the maths tests struggled on this one.
Hope this helps in some way - sorry I cannot expand further.