Brakes, Very Simple But Extremely Complex and Hard to Understand

Aircraft Brake Maintenance Tips

The brakes on small airplanes such as a Cessna 172 or Piper Warrior are very simple and easily operated. You push on the pedal and a pressure to the calipers and pads work their magic squeezing the brakes together. It is that simple

​Now we move up to the more complex brakes on heavier aircraft. They use a different type of brake pad system. They are not material type pads with metal flakes in them they are actual metal pads pushing against a thick metal rotors. These are metal to metal brakes. You first statement becomes “how do metal to metal brakes possibly stop an airplane that weighs up to 7700 pounds. Well, actually very well. Metal to metal brakes have been perfected and if they are installed correctly and “GROUND IN TO THE ROTOR”, they will work to the point of stopping the tire which can flat spot the tire. These metal brakes to a metal rotor are better than fabric material brake pad to a metal rotor.

​Fortunately, I spent many years in the automobile business in the 70’s along with being a aviation mechanic and lots of other professions and businesses. I worked on the early stages of metal brake shoes to drum brakes. We found that when you install metal brake show pads to old style drum brakes, the drums needed to be “pre-prepped” to accept the metal brake pads. “Pre-prep” means the drums have to be “roughed up” for the new shoes to grind their way into the older drums. From this I became an expert on metal to metal brakes such as large aviation brakes using metal pads to metal rotors.

​Let me get this out of my system. The large thick rotors on the bigger airplanes really never have to be replaced. They are thicker than is really needed to make them work. There are mechanics who want to replace the rotor when they replace brake pads or do major brake work. This is really unnecessary. The metal brake pads will wear out before the rotor gets close to being replaced. In fact in years of working with large brakes, the rotors are NEVER replaced just reconditioned. So the problem is how do recondition the brakes.

​You must sand (emery cloth at a minimum) down the rotors to rough them up. If they are roughed up then the new metal pads seat. How do you seat the metal pads after you “rough up” the rotors? On the ramp you start the plane moving while you hold down the brake pedal just lightly grinding in the new brakes to the roughed up rotors. You may have to do this for quit a few times. Roll the plane and grind in the brakes slowly into the rotors. Do this until you get a standard braking response.

​Remember, don’t fall for the “we put a micrometer on the rotors and they need to be replaced” sales pitch. The rotors on the large aircraft are thick for a reason, to take the heat and stop the plane. It is the metal pads that wear out, not the rotors.

​Fly safe and learn your systems.

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