An APC is "Assesment of Prior Competence" and is done if your student rating lapses before you start unit training. It is usually a short course (2 days or so I think) in the sim to check that you still remember the stuff you need to train.
If he has the chance to go with NATS though why not go for that, they will pay you to train, which is a lot cheaper than paying to do it (and then have to hunt for a job). It might be slow but still seems a much better option to me...