I can give you some info. I think overall there are about 1100 pilot spots every year. Air Force academy gets 500-550 spots. Rotc gets somewhere between 350-450 spots depending on who you talk to on this forum and the rest go to OTC. Per Wikipedia, AF Rotc commissioned 2083 officers in 2006. I dont know how that compares to 2018, but lets assume its close. So if we split the difference and go with 400 spots, 400/2083 = 19%. Of course not all of those 2083 who commissioned qualified for or even wanted to be a pilot, so the percentages get better. Having said that, dont have official numbers, but people on this forum have said that may 25% of those who start Rotc, actually finish and commission. For one reason or another the rest quit.
Getting a pilot spot assuming you qualify medically is rather easy as long as you do well in things they look for. Having said that, you could do great in all these things and still not get a pilot spot. Why, its a mystery. There are plenty of people who do well in all aspects and still dont get a spot.
This is what you need or do well in order to get a spot
1. Private Pilot License- There is no requirement for one and they will tell you plenty of people gets spots without ever being in the air once. This is completley true, but having a license is to your advantage
2. Have a good GPA over 3.0 . The irony of this is that depending on the time period, like right now, having a 3.5 in a humanities could be more advantage than getting 2.9 in Aeropsace engineering. Having said that, I think they give preferences to the those with STEM majors
3. Do well on the AFOQT which is like a SAT/ACT test that has a pilot and navigation section. My son got a 95 on pilot and I have to assume a big part of it is that he had around 150 hours of flight time at the time.
4. Do well on the TBAS test which a computer test of basic aviation skills. Again flying skills and I think video game playing helps with that. The test is sort of a mystery and while there is some info on it, the cadets are not allowed to discuss this test
5. Get a high PCSM score. This is score that is made up of #3, the pilot portion of the AFOQT test, the score from #4 the TBAS test and #1, number of flight hours. My son PCSM score with out flying hours was 70. With the flight hours it was 98. 99 is the top score. I read somewhere that the average scores for those who make UPT is something like in the 70s or so.
6. Get a high PT score (physical training)
7. Get invited to Field Training which occurs in the summer between Sophmore and Junior year. The last two years, approx 90-100% of those in Rotc where invited. Not only must you pass the course, but you will be rated and you need to be somewhere between middle to high. This year they are talking that maybe 75% or so will be invited. This is regardless if you have a scholarship or not. Too many people in Rotc and not enough spots. The advantage I hear is to those who have STEM majors with better than average GPAs. This of course contradicts what I said in #2 regarding grades and majors.
8. Finally, you commander will rate you. Again middle to high would be preferable.
There are two type jobs in the Air Force, rated and not rated. If you want to be a pilot, you then apply to the rated board and all this info is given to them. Here is the kicker, there are 3-4 other rated jobs. They include RPA (drones), CSO (navigator) and 1-2 others. When you apply you will tell them that you want Pilot first and CSO second and so on. The board then decides and can give you Pilot or any other 3-4 other rated positions. If you get Pilot, then you are all set except you then need to get a full Pilot phyiscal where you can pass or fail depending on your physical and many cases your visuual situation. Lets say that give you CSO. If you take it but still want to be a pilot, there is a chance that they may latter bump you up to pilot. As people fail their pilot physical or for other reason, spots open up and some people get up bumped from what they were offered to pilot. If you dont accept CSO or whatever was offered, then you are done and you can never apply for another rated position. Now once you become active duty, you can apply for a pilot spot or any other rated position. These are people who were never offered a rated spot in the first place. As I said before supposedly if you were offred CSO and you turned it down, you arent supposed to be able to apply again when you are active duty. Others in the board have said that the AD boards may not care or even know that you turned down a rated position while in Rotc. Who knows and probably better to play it safe. Hope this helps