Definition
An aircraft hydraulic brake arrangement that uses two independent brake systems — System A and System B — operating on the same wheel brakes. Each system has its own hydraulic supply, pressure source, and lines, so that if one system fails or loses fluid, the other continues to provide braking through the same brake assemblies.
Plain English
A wheel brake setup with two separate hydraulic systems feeding the same brakes. If one fails, the other keeps the brakes working.
Context Anchor
Seen in aircraft systems descriptions, maintenance manuals, and abnormal procedures for aircraft that have more than one hydraulic brake supply.
Derivation
Hydraulic comes from Greek words connected with water and pipes, and now means using liquid to carry force. In this term, A and B are simple labels for two separate fluid-pressure systems.
Why Pilots Care
Ensures braking remains available after a failure in one hydraulic circuit, supporting safe ground handling.
Grounding Statement
Picture the wheel brakes being fed by two separate fluid-pressure paths, so one path can still help operate the brakes if the other path loses pressure.
Intuition Check
A&B does not mean two sets of brake pedals or two grades of brakes. It means two separate fluid-pressure supplies or paths, labeled A and B.
Example Sentence 1
After the System A pressure dropped during taxi, the crew confirmed the A&B hydraulic brake system was still providing normal braking through System B.
Example Sentence 2
During the preflight walk-around the pilot confirmed the A&B hydraulic brake system showed normal readings on the gauge.