Aircraft Maintenance: Take a break to learn about your brakes

Aircraft brake systems don’t usually get too much attention until something fails. That’s risky because a failure in the brake system can cause a lot of damage. It pays to stay ahead of the maintenance curve and look for trouble before it finds you.

On most aircraft, the major brake system components are easy to access and inspect. On certified aircraft, brake maintenance is not a legal owner-maintenance task. However, there is an interesting twist in the federal aviation regulations: While brake system maintenance is not included on the list of legal preventive maintenance items, changing tires is. Changing a tire requires wheel removal, which requires brake caliper backing plate removal … you get the picture.

At the very least, it makes sense for all aircraft owners to have a full understanding of how their aircraft’s brake system works and how to inspect it properly. Again, our goal is to spot minor problems before they become major ones!

While many types of aircraft brake systems exist, the most common by far are the Cleveland (Parker) systems used on most Cessna, Piper, Beech, and Grumman aircraft. The basic design is simple: When a brake pedal is pressed, a master cylinder attached to the brake pedal forces hydraulic fluid through the brake lines to the brake caliper at the wheel. Because differential braking is critical to the operation of many aircraft, there are two separate brake systems: one for the left brake and one for the right.

The typical general aviation aircraft has no pumps, antilock components, or hydraulic assist. Hydraulic fluid is supplied to the master cylinders from a reservoir. Some aircraft, such as Grumman single-engine models, have an internal reservoir, which is found in master cylinders. In other aircraft, such as most Piper and Beech models, the master cylinders are supplied by a reservoir mounted on the engine side of the firewall. It looks just like someone took the can that the fluid came in, welded on a tube at the bottom, and bolted the can to the firewall—which is basically what they did.

The reservoir feeds the master cylinders, which are found behind the brake pedals. In aircraft with both pilot and co-pilot brakes, there are four master cylinders, one for each pedal. Typically, the flow of fluid from the reservoir goes to the pilot-side brakes first, then to the co-pilot side. If the system uses internal reservoirs, those also will be found on the pilot side.

Following the master cylinders, the pressurized hydraulic fluid is routed through a series of flexible hoses and hard lines through the airframe and down to the slave cylinders on each main wheel. Often, there is a parking brake valve that is also inline between the two.

At each wheel, a slave cylinder integral to the brake caliper contains a piston (or pistons) that expands, clamping the brake pads on a metal brake disc attached to the wheel. The brake pads are designed to supply the friction for stopping and to serve as the primary wear surface, rather than the disc. There are other designs, but they all employ the same basic concepts and flow of fluid.

Next time, we’ll look at common points of failure and how you can spot small issues before they become big ones. Until then, happy flying!

Interested in aircraft maintenance? View the archives of Jeff Simon’s Aircraft Maintenance series.

Jeff Simon is an A&P mechanic, pilot, and aircraft owner. He has spent the last 14 years promoting owner-assisted aircraft maintenance as a columnist for several major aviation publications and through his how-to DVD series: The Educated Owner. Jeff is also the creator of SocialFlight, the free mobile app and website that maps over 20,000 aviation events, airport restaurants, and educational aviation videos, including many how-to videos for the subjects of these articles. Free apps are available for iPhone, iPad and Android, and on the Web at www.SocialFlight.com.