Each system is characterised by the replacement items it consists of i.e. both repairables and discardables. Each item is then characterised by its content of replacement items until a complete system breakdown structure has been defined. In this sense OPUS10^TM is a true multi indenture model with no basic limitation on the number of indenture levels.

The term indenture level was used to give a point of reference only. As a matter of fact OPUS10^TM is not at all constrained by the motion that an item belongs to any particular indenture level. This is an important feature. An aircraft engine is such an item, where it is sometimes replaced on the aircraft while for certain failures; repairs will be affected by replacement of modules.

OPUS10^TM will model:

• Assemblies
• Line replaceable units
• Shop replaceable units
• Partly repairable line replaceable units
• Partly repairable shop replaceable units
• Discardable units
• Discardable parts

From the perspective of the logistics support system, the sites with systems and item breakdowns are entities that generate demands for maintenance and the supply of spares. These demands are specified in terms of failure rates or replacement rates, as appropriate, for all items in the system breakdowns.

OPUS10^TM allows the sum of failure rates for items belonging to an item to be less than the specified failure rate for the mother item. The residue failure rate would then correspond to instances when repair is affected without use of a replacement item. OPUS10^TM is also capable of modelling false replacements, No Fault Found and Scrap.