What It Looks Like

Airplanes are just not very efficient for getting around on the ground. With their outstretched wings and spindly three-legged gear, they are unsteady, especially in any kind of wind. The propeller is the only way to get and keep the airplane moving, and the steering efficiency compares more with a large boat than a car. Also, where a car has large disc or drum brakes on each of its four wheels, a light airplane has brakes only on its main wheels, and they are relatively small.

Airplane brakes are disc brakes. A metal disc is bolted to the main wheel, and a caliper assembly envelopes a small portion of the disc. This caliper houses one or more brake pads on each side of the disc. When you apply the brakes, you are moving a piston in a master brake cylinder that forces hydraulic brake fluid through lines to the brake calipers. The fluid pushes against pistons in each of the calipers, which in turn push brake pads against the discs to slow and stop their rotation. It's a simple squeeze play, with the brake pads doing the squeezing.

The friction and resulting heat cause wear to the brake-pad linings, which are made either of non-asbestos organic material or a metallic compound. To keep pad and disc wear to a minimum and ensure the long life of brake components, use the brakes properly and judiciously. Avoid panic stops, keep your feet off the brake pedals on the takeoff run and when touching down on landing, use the brakes sparingly when taxiing and only when you've pulled the power to idle.

One of your preflight checks should be to examine the brake pads. This isn't always easy, especially if the airplane has wheel pants that enclose the wheel assembly.

If you have visual access to the discs and pads, check to make sure the pads have at least 0.1 inch of material remaining, which is about the thickness of two quarters squeezed together. That's the minimum thickness allowed before they must be replaced. If the pads on the airplane you're about to fly are at, or nearly at, that minimum thickness, you may need brake maintenance.