About occurrence effectivity

The effectivity of an occurrence can be expressed as a date range or a range of units with respect to an end item. An occurrence can have multiple expressions comprising date effectivity, unit effectivity, or both. Multiple unit effectivity expressions may reference the same end item or different end items. If no occurrence effectivity is specified, the occurrence is considered to be always effective; that is, it is not constrained by any effectivity definition.

Occurrence effectivity is used principally for two purposes:

• To reflect changes to the structure over time as new parts replace old ones.

• To explicitly state the content of a unit or range of units as a means of managing the variability of the product. This technique is an alternative to using options and variants to configure the parts needed to fulfill a particular offering.

Occurrence effectivity is frequently used by manufacturers of military and aerospace products. The end item may correspond to a serial number or the tail number of an aircraft.

For example, there may be different hydraulic cylinders in the landing gear of an aircraft, depending on whether the aircraft is certified for unimproved runways. There may be additional differences to the aircraft to meet this purpose, such as debris deflectors, wheels, and tires. Using options and variants, you could define an option called RW_Class = Paved or Gravel, and there would be a variant rule on stouter cylinder to configure it in for the Gravel option. Using occurrence effectivity, the unit number of each aircraft unit that is certified for operation on gravel runways (for example, units 3-6, 17, 33-45) would be used in the effectivity specified for parts such as stouter cylinders. The effectivity of the regular cylinder would be specified using the other units (unit 1-2, 7-16, 18-32, 46-up).