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News & Media How it works: Brake system

How it works: Brake system

Friction will stop you in your tracks

January 1, 2017 By Jill W. Tallman
For something that has such an important job, the brake system on a light aircraft is simple. 
January Preflight
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Treat brakes gently

Brake linings wear out when they are used, so it makes sense that if you can use them as little as possible, they will last longer. Once you become comfortable taxiing an airplane, your next lesson should be to try not to ride the brakes while on the ground—a sin that many pilots commit without realizing it. Taking that strategy further, use little or no brakes on touchdown. If traffic permits, you can even roll to the end of the runway to pamper your airplane’s brakes even more.

A Cessna 172, for example, uses a single-disc system. When you press on the toe brake, a master cylinder that’s attached to the brake pedal pushes hydraulic fluid through hoses and rigid lines to a brake-unit housing attached to the landing gear strut. A piston within the housing responds to the pressure by pushing against a lining, which then pushes against a brake disc, which in turn pushes against a stationary lining. The equal friction on both sides of the disc is what slows and stops the airplane. If an airplane is equipped with pilot and co-pilot toe brakes, there will be a master cylinder and reservoir for each brake—and also one for the parking brake.

What to look for on a preflight

• Leaking hydraulic fluid is a bad sign on two fronts: It means the brake system has lost the fluid it needs, and air has likely been introduced into the system. Don’t fly until a mechanic has checked it. Not all hydraulic fluid leaks are external; some can occur within the system where you would not ordinarily see the evidence.

• Look at the linings. Are they the correct thickness or wafer-thin?

• Check brakes after engine startup. If the pedal does not move, or if you detect sponginess, a hydraulic fluid leak may be to blame.

Jill W. Tallman
Jill W. Tallman
AOPA Technical Editor
AOPA Technical Editor Jill W. Tallman is an instrument-rated private pilot who is part-owner of a Cessna 182Q.
Go to Jill W. Tallman's Profile

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