Acronym
The singular and plural of an acronym are always spelled the same.
AGANAs Good As New
ABAOAs Bad As Old
CMCorrective Maintenance
PMPreventive Maintenance
IFRIncreasing Failure Rate
DFRDecreasing Failure Rate
IFRAIncreasing Failure Rate on Average
DFRADecreasing Failure Rate on Average
NBUNew Better than Used
NWUNew Worse than Used