In the early days, there were two kinds of CM philosophies:
1) Collect lots of data, use it to write obituaries on failed engines.
2) Collect lots of data, analyze it while it still means something, and make more intelligent decisions.
Long-haul operators found that it was possible to cut their number of schedule disruptions (out-station removals, unscheduled maintenance...) by intensive CM. Changing an engine half-way around the globe is - ummm - expensive! One or two of these pays for a lot of CM; Better to change it before departing home.
(I trained a lot of F/E's in manual data collection & analysis, a long time ago...)
