Definition
A rigid metal tube or flexible reinforced hose that carries hydraulic fluid under pressure from the brake master cylinder to the wheel brake assembly. Brake lines must withstand high pressure without leaking and are routed to allow normal landing gear and wheel movement without chafing or kinking.
Plain English
The pipe or hose that carries brake fluid from the brake pedal system down to the wheel, so pressing the pedal makes the brake squeeze the wheel.
Context Anchor
Seen during preflight inspection, maintenance, and troubleshooting of aircraft wheel brakes.
Derivation
Line comes from a word meaning a string or cord, and later came to mean a long, narrow connection. In aircraft systems, a line is usually a tube or hose that carries fluid or air from one place to another.
Why Pilots Care
A leak, crack, or blockage in the brake line can cause partial or total loss of braking, creating a serious safety risk during taxi, landing, and parking.
Intuition Check
A brake line is not a painted line or a checklist item. In this context, line means a physical tube or hose that carries brake fluid.
Example Sentence 1
During preflight, she noticed a small wet patch near the brake line at the left main wheel and grounded the aircraft for maintenance.
Example Sentence 2
The mechanic replaced the chafed brake line before the next flight to restore full braking pressure.