TM 10-3930-671-24 Safety and Operational Checks PM Interval A = 8 - 10 hours, or daily B = 50 - 250 hours, or every month (Typical PM interval) C = 450 - 500 hours, or every 3 months D = 900 -1000 hours, or every 6 months E = 2000 hours, or every year F-39