What It Looks Like

Most braking systems on light aircraft are hydraulically actuated, the same as on most automobiles. When you depress the brake pedals (or, in some aircraft, pull on a lever extending from under the instrument panel), the brake master cylinder (or cylinders) forces hydraulic fluid through small-diameter metal lines to the brake assembly on each main landing-gear wheel. The pressurized fluid acts to squeeze brake pads against the rotor, slowing the rotation of the wheel.

A good preflight inspection includes checking the main wheels and brake assemblies to ensure that brake pads and brake rotors are in good condition. But what about the brake fluid? How can you check to see if the fluid level is within limits or needs replenishing?

The answer can be found in the pilot's operating handbook or airplane flight manual. It may be in the section describing aircraft systems, or under handling, service, and maintenance. The information should include the location of the brake fluid reservoir, how often it should be checked, and what to use when replenishing the fluid.

The information is different for different aircraft. For example, the reservoir on most Pipers is located on the firewall separating the nose section from the cabin (see photo). The nose cowl must be removed to gain access to the reservoir tank. Unscrew the cap and peer inside to check the level of the MIL-H-5606-specification brake fluid. The fluid should be checked at least every 50 flight hours (100 hours on some aircraft - check the POH to make sure), or whenever brakes do not perform up to par.

Cessna takes a different design approach. The brake fluid reservoir is located on the brake pedal/master cylinder assembly attached to the rudder pedals. To check fluid level, you must crawl underneath the panel and unscrew a small metal plug.

Whether Cessna or Piper, checking brake fluid level is not the easiest systems check to perform. Fortunately, it's done only occasionally.