Five different maintainability methods are documented in MIL-HDBK-472. The different prediction methods address different aspects of
maintainability and each method predicts maintainability using different metrics.
Procedure I - This procedure typically is intended to be used to predict flight-line maintenance of airborne electronic and electromechanical systems involving modular replacement. It uses a calculation procedure based on a list of elemental activities for which normalized distributions and occurrence probability are given. The parameters used in this method are: the distribution of downtimes for various elemental activities, maintenance categories, repair times, and system down time.
Procedure II - This procedure typically is intended to be used to predict the maintainability of shipboard and shore electronic equipment and systems. It could be used to predict the maintainability of mechanical systems provided that task times and functional levels could be
established. Procedure II contains two different approaches, Part A and Part B.
Part A: The parameter used is corrective maintenance time expressed as an MTTR in hours.
Part B: The parameters used are: active maintenance in terms of mean corrective maintenance time in labor hours, mean preventive maintenance time in labor hours, and mean active maintenance time in terms of mean manhours per maintenance action.
Procedure III - This procedure typically is intended to be used to predict the mean and the maximum active corrective maintenance down time for Air Force ground electronic systems and equipment. It also can be used to predict preventive maintenance down time. The parameters used in this method are: mean and maximum active corrective down time (at the 95th percentile), mean and maximum preventive downtime, and mean downtime.
Procedure IV - This procedure is intended to be used to predict the mean or total corrective and preventive maintenance downtime of systems and equipment. The parameters used in this method are: mean system maintenance downtime, mean corrective maintenance downtime per operational period, total corrective maintenance per operational period, and total preventive maintenance downtime per operational period.
Procedure V - This procedure was developed much later than the other four procedures and is by far the most versatile. Typically it is used to predict the maintainability parameters of avionics, ground and shipboard electronics at the organizational, intermediate and depot levels of maintenance. It presents a tabulation of time standards in relation to illustrations of what each time represents. The parameters used include: MTTR, MMax ( ), MMH/repair, MMH/OH and MMH/FH
Significantly, all commercial computer software
development to date has concentrated on Procedure V, to the exclusion of the
other four maintainability prediction procedures. Therefore, only the
procedure previously designated as "Procedure V" in MIL-HDBK-472 has been
included as Appendix D , "Maintainability Prediction" in this handbook.