I don't know details, but you couldn't just sign up for it. They were all officers, for one thing, which means they were all from the upper classes.

>>1310910
Most were already civilian pilots before the war and simply turned military when the war started

>>1310910
Today, all pilots of military aircraft are officers. That means they graduated college or went through a military academy (college+bootcamp for officers). I imagine the same must have applied for WW1.

So I imagine only well educated individuals from a most likely wealthy background were capable of being pilots. The military probably advertised it as a program for anyone interested.