In my entire career I only came across one AF Warrant Officer on active duty. I was going through tech school at Chanute and he was in charge of the school.
I believe that the AF utilized the WO1 rank for a short period of time back during the early 70's. This was for Physician Assistants during their 2nd year of training. After training they receive their commission of 1st Lt. (Most of the PA's students accepted into the program were low ranking NCO's (E4-E5) in the 902X0 career field.)