Does an Inter-Service Transfer from Army to Air Force happen often or is that a rare occurrence?

SGT (Join to see) They occur, but are not common per the link below. If you enter "Inter-Service Transfer" in the Search bar above, hit enter, and then click on "Answers', you will find other Posts that deal with this topic.

https://www.thebalancecareers.com/transferring-between-military-branches-3357016

It's a lot easier for chaplains than for many other MOS's and therefore relatively more common. I transferred from the ARNG to the AD Navy. Interservice transfers tend to happen more frequently when moving from the active to reserve components.