You will need to provide a 20 minute lecture on propellor theory, with specific reference to Assymetric Blade Effect. Also, you will have to demonstrate on paper that you can derive Bernoulli's theorem from first principles.
As for the interview, I hope you can do mental trigonometry, otherwise you have no chance. And then there is the physical. You ever heard how for SAS selection you have to run up Pan-Y-Gent mountain, in Wales? Atlantic make you do it backwards. Blindfolded.
But I wouldnt worry about spelling.
Go for it guys, it is worth it...