I think you've got good options there, both the apprenticeship and the A-levels. Working with aeroplanes is good, at many levels, despite a few jaded individuals above.
A-levels are pretty much a necessity for many things - for example if later you want to do an Engineering degree, they will put you in a better position than an NVQ4 will alone. I'd suggest going to the potential sponsor and saying that you desperately want to do the course, but equally want to complete your A-levels. Ask the straight question of whether they can either give you a years deferment, or provide opportunity for you to complete your A-levels whilst with them. If they are a decent employer, they should be able to make room for one of these options.
G