Line Replaceable Unit, or Avionic Line Replaceable Unit. This is an important concept as it ties in with the privileges relating to tasks a B1 licence holder can or can’t perform. For a piece of equipment to be considered an LRU, it must satisfy the following three conditions (Reference: Part 66 MOS Page 2).

1. It must have no mechanical input to, or mechanical output from, another component.
2. It must contain only electrical, electronic, instrument or radio parts and/or software.
3. It must not require specialist knowledge or specialist equipment to install or test functionality.

In summary, an LRU can be thought of as a “black box” component. It is simply a “plug and play” device with only an electrical connection.