Your union local should have given you a contract book that includes both the National Master and local supplement. Keep it in your car or somewhere you can always get to it. Anyway:
From the National Master:
a. Part-time air drivers including exception air drivers will be paid as follows:
Start-$12.50
Seniority-$13.50
Seniority Date plus 12 months-$14.00
Seniority Date plus 18 months-$14.50
Seniority Date plus 24 months-Top Rate
Air driving rate progresses by time that's passed since you first punched in as an air driver. So it's different from full time progression for which you have to actually bank worked days for to move up to top rate. In my area top rate for air drivers is a huge jump from seniority date plus 18 months.