Life-limited parts

Life-limited parts (LLP) are parts that have a predictable aging profile and have significant consequences if they fail, and therefore have a specified service life. A life limit can be defined by accumulated cycles, hours, or any other mandatory replacement limit of an LLP. This means each of these LLPs can only operate a certain number of flight hours, flight cycles, or other pre-determined parameters before it is removed from the aircraft and destroyed. LLPs cannot be restored and must be discarded upon expiration.

Typically, the manufacturers determine the life limit of a part, which is described in the manufacturers' maintenance documents or instructions for continued airworthiness. In some cases, the life limits for a part may be updated as described in an SB or an AD. These guidelines are used to determine the part number's life limit in Maintenix. Most LLPs are governed by either the number of flight hours operated or the number of flight cycles operated, so in those cases, the part's expiry is reached when the set number of hours/cycles are collected.

In Maintenix, component life limits are modeled as discard requirements, i.e. requirements with a task class of DISCARD. The life limit itself will be recorded as the discard requirement’s scheduling threshold. By using requirements to model life limits, Maintenix is able to ensure that hard-time discard tasks are visible to all users, usage is properly tracked and accounted for, and the necessary procedures can be invoked when the component’s life limit is reached (such as a component removal and scrapping).