Line Replaceable Unit
LRUSection 11: Aircraft & Avionics Architecture
Definition
A modular component or assembly of an avionics system designed to be removed and replaced at the aircraft (at the flight line) by maintenance personnel without specialized tools or extensive disassembly, enabling rapid return of the aircraft to service. LRUs are the fundamental unit of line-level maintenance and typically include the complete electronic assembly in its enclosure with connectors, mounting hardware, and a nameplate identifying part number, serial number, and modification status.
Where This Shows Up
The LRU concept is central to avionics maintainability and dispatch reliability. When a fault is detected, maintenance personnel remove the suspected LRU and install a serviceable replacement, returning the aircraft to service in minimum time. The removed LRU is then sent to a repair shop (Part 145 / EASA Part 145 facility) for diagnosis and repair at the SRU level. LRU design must consider ease of access, connector keying to prevent incorrect installation, and built-in test (BIT) capability to support fault isolation to the LRU level. The aircraft Fault Isolation Manual (FIM) and Illustrated Parts Catalogue (IPC) define the LRU-level maintenance procedures.
Primary Sources
Operator/Manufacturer Scheduled Maintenance Development — the maintenance philosophy that defines the LRU/SRU concept within the maintenance program structure.
Related Terms
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