To take charge of men and be responsible for their work, welfare and discipline
All of the above is irrelevant. An Officer in the RAF has to be all things to all men*. Having a good command of English is only a small part of the big picture. It's no use if you don't actually communicate very well, or have the other Officer Qualities that OASC look for.
In these times, the RAF can be really, really picky.
*and women