Which statement best describes the difference between a Line Replaceable Unit (LRU) and a Shop Replaceable Unit (SRU)?

• A. An LRU is replaced in a maintenance shop and generally requires more extensive servicing.
• B. An LRU is designed to be quickly replaced at the aircraft level (line maintenance).
• C. An LRU is used for software modules; SRU for mechanical components.
• D. An LRU is a warranty term; SRU is a test unit.

Answer: (B)

The key idea is where and how the unit is serviced. A Line Replaceable Unit is designed to be swapped quickly on the aircraft during line maintenance, so the airplane spends minimal time on the ground and a ready-to-install unit can be quickly fitted with simple tooling. This modular approach lets crews replace faulty components fast without pulling the aircraft into a shop.

A Shop Replaceable Unit, by contrast, is meant to be repaired or replaced in a maintenance shop, involving more extensive disassembly, testing, and calibration in a controlled environment. So the best description is that a Line Replaceable Unit is designed to be quickly replaced at the aircraft level, enabling fast line maintenance. The other distinctions—software versus mechanical components or terms like warranty or testing—don’t define LRUs versus SRUs.