He is getting basic flying training, he is learning the basics of how to fly different types of plane and helicopter as part of his attachement to the RAF where's he's learning basically how the other services work and see how it differs to the army (like them doing less work than us
), he'll have the rank of Flying officer and wear an RAF unifrom while he's with them for his 4 months, and supposidly will mingle with the peasant airmen and NCOs too !
The main reason he's doing this is because as monach, he will one day be head of the armed forces and so need to know how all 3 services are like, how they work etc, after this I beleive he's going to train on how to 'drive' submarines with the Navy.
As I said, his flying is PART of his experiance, it's not the actual reason why he's going (officialy atleast).
He'll earn his basic wings, which provided that he passes the tests, means he will be able to fly solo, perform basic aerobatics, deal with mid-air emergencies and fly in formation.
The normal RAF pilots have much longer courses because unlike the Prince, they are training for their job and hence need much longer training, this is like the differance between someone earning their PPL and getting an ATPL or, the differance between learning to drive a normal car and a Rally car, the training is much different because they are different things.
Always stand up for what is right, even if it means standing alone..