The problem with complex machinery is that if they do not run, fly, or swim on a regular basis, they break when you turn them on. But that is not all, when your wing reduces flying hrs, Maintenance is affected because they do not have the experience of doing what they do best -- maintain -- the jets. New maintainers takes longer to certify even on the basics of whatever their specialty, and experienced maintainers gradually lose proficiency. Maintenance records contributes to that misleading availability statistics. If once a jet is signed off as mission capable but does not fly for a couple weeks, the odds of something go wrong on engine start increases. A typical squadron have about 12 to 20-something jets, depending on the platform. When I was active duty, we did not have simulators like today, so each of our jets take off at least once a week, assuming the standard 5 days flying schedule. This would create the truer Mission Capable (MC) rate.
If a jet is 'available' it does not mean it is 'mission capable'. The Thunderbirds F-16s can be made 'available' with a stroke of the pen -- they are flying -- but would hardly be 'mission capable'. Not without a lot of hangar time.
If a jet is at Depot level maintenance, the jet is literally off base and with the manufacturer. But if a jet is at Phase level maintenance, the jet is still on base and in wing possession but is not in flyable condition. Here is where the 'fudge' factor come in. A jet in Phase maintenance can be rendered flyable condition in a few days, then passed the Functional Check Flight (FCF) and become Mission Capable (MC) again. The jet in Phase maintenance can be fudged into the MC rate.
The Aircraft Available (AA) rate is based on all the jets the squadron own. The Mission Capable (MC) rate is based on actual flyable jets.
Let us say a squadron have 20 jets. Five are at Depot which make 15 on base. The AA rate is 15/20 or %75. However, of that 15 on base, three are in Phase maintenance leaving 12 on the ramp. The MC rate is 12/15 or %80. War planning with the 12 jets on the ramp would be realistic because that is all the squadron is capable to send even though the 3 jets in Phase could be out in a week. Similarly, if a mission require 20 jets but the squadron have only 12, either the squadron would be partnered with another squadron or be dismissed from the mission.
Platform reliability affects both the AA and MC rates, however, its greatest contribution is at the MC rate. In wartime, Depot and Phase maintenance schedules would be discarded. Some time compliance maintenance schedules, such as an engine change after X flight hrs, would be delayed, but not entirely discarded. Platform reliability is critical if the mission is expeditionary where the longer the physical logistics distance, the greater the vulnerability of that supply chain.
Platform reliability must have few, preferably zero, system errors that 'Cannot be duplicated' or 'Retest OK'.
apps.dtic.mil
This study focuses on the aircraft avionic maintenance problems of cannot duplicate CND and retest-ok RTOK for three sampled F-16 wings.
CND/RTOK events occurs more often than most people think. Even civilian airliners have them. What happens is that the pilot write up the jet but Maintenance cannot find the error, so the jet is taken off MC status for further investigation. Avionics produce the most CND/RTOK write-ups. Other systems such as engine or environmental have more mechanical components in them so they usually produce hard errors. Of course, taking a 20 mm round will definitely produce a hard error no matter what system. CND/RTOK write-ups negatively affects logistics because LRUs that are removed for troubleshooting must be tested before they can returned to the supply chain. Any jet that have intermittent CND/RTOK write-ups in wartime will be removed from the lineup and cannibalized for parts.