Aviation Brakes: Aircraft Braking Systems Glossary

An aviation brake is an energy-absorption assembly engineered to decelerate an aircraft during landing ground roll, rejected takeoffs, and ground maneuvers, while also securing the airframe during ground holding and engine run-ups. In general aviation and light turboprop applications, landing gear configurations commonly employ independent, hydraulically actuated disc brakes keyed to the main landing gear wheels. Braking assemblies operate under severe thermal and mechanical stresses and represent critical landing gear components within broader Airframe Parts catalogs. Technicians sourcing replacement assemblies or maintenance hardware can browse the inventory at American Aviation Parts across All Products.

Bleed Valve

A threaded, hollow maintenance fitting located at the highest elevation of the brake caliper cylinder assembly. The bleed valve allows air bubbles and contaminated hydraulic fluid to be purged from the brake line during servicing. Because air is compressible, any air entrapped in the lines causes a spongy pedal feel and diminished braking authority. Pressure bleeding equipment or specialized hand pumps connect to the bleed port using dedicated hydraulic Adapters to force MIL-PRF-5606 or equivalent fluid upward into the reservoir in accordance with the aircraft maintenance manual (AMM).

Brake Caliper

The structural housing—either fixed or floating—that straddles the brake disc and houses the hydraulic cylinder bores, actuating pistons, and brake linings. In a typical floating caliper configuration, the caliper slides axially on torque pins or anchor bolts. When hydraulic pressure is applied from the master cylinder, the piston displaces the inner lining against the rotor while the caliper body reacts by drawing the outer lining into equal contact on the opposite face.

Brake Disc

The rotating flat circular steel or nickel-plated plate that is keyed directly to the aircraft wheel half and rotates at wheel speed. The disc absorbs kinetic energy and dissipates it as friction-induced heat when clamped by the stationary brake linings. Discs must be inspected regularly for minimum thickness, dishing, pitting, thermal cracking, and corrosion. PMA replacement discs from manufacturers such as APS are widely utilized across certified fleets. A common general aviation example is the Brake Disc Aps 164-06406, which must always be measured using calibrated Aircraft Brake Tools against the wear limits specified in the component maintenance manual (CMM).

Brake Lining

The consumable friction block (often referred to as a puck) riveted or pinned to the pressure plate and backplate inside the caliper. Linings are fabricated from organic, semi-metallic, or sintered metallic compounds designed to maintain a consistent friction coefficient across high operating temperatures without galling the disc. Linings must be replaced when worn to the minimum dimension prescribed in the manufacturer's illustrated parts catalog (IPC). For details on replacement eligibility and regulatory approvals, consult our technical resource on FAA PMA Parts Explained - American Aviation Parts.

Brake Master Cylinder

A mechanical-to-hydraulic transducer linked directly to the pilot's and co-pilot's rudder toe pedals. Depressing the upper portion of the rudder pedal moves a piston shaft within the master cylinder bore, pressurizing fluid through flexible hydraulic hoses and rigid lines down to the brake caliper. Many general aviation aircraft feature integral fluid reservoirs on each master cylinder, while others route fluid from a centralized airframe header tank.

Brake Piston

The cylindrical actuator positioned inside the brake caliper bore that translates hydraulic pressure into mechanical clamping force. Brake pistons are typically machined from aluminum alloy or phenolic resin to minimize heat conduction from the friction interface back into the hydraulic fluid. Severe overheating can boil fluid inside the caliper bore, resulting in catastrophic loss of braking capacity during high-energy stops.

Caliper Anchor Plate

A stationary, high-strength mounting flange bolted to the landing gear axle assembly that supports and aligns the floating brake caliper. The anchor plate features precision-machined guide bushings that allow the caliper pins to slide smoothly without binding. Because extreme braking torque transfers directly through this plate into the gear leg, proper bolt torque and safety wire retention must be verified according to the applicable AMM.

Parking Brake Valve

A dual-circuit, pilot-operated hydraulic shutoff valve plumbed between the master cylinders and the wheel calipers. When the pilot depresses the toe brakes and engages the parking brake control handle, the valve closes, trapping static hydraulic pressure in the caliper cylinders to keep the linings clamped against the rotors. Because significant thermal dissipation occurs after landing, maintaining the condition and inflation pressure of Aviation Tires is essential to avoid wheel hub overheating when the parking brake is set on hot assemblies.

Shuttle Valve

An automatic selector valve incorporated in dual-control cockpit installations that prevents cross-bleeding between the left-seat and right-seat brake master cylinders. When one pilot applies brake pedal pressure, an internal sliding spool or shuttle shifts to seal off the opposing pilot's master cylinder circuit, directing pressurized fluid straight to the brake caliper without allowing fluid to backfill the inactive master cylinder reservoir.

Wear Pin

A calibrated mechanical indicator pin protruding from the exterior of heavy-duty or multi-disc brake calipers that allows maintenance personnel to evaluate lining and disc stack wear without disassembling the wheel assembly. As the friction surfaces wear down over successive operational cycles, the pin recedes into the caliper housing; when the pin head becomes flush with the reference shoulder, the brake assembly has reached its service limit and requires overhaul or relining as dictated by American Aviation Parts technical references and certified maintenance data.