The wheels and brakes of our aircraft slosh through rain, sleet, and snow, ensuring that the time we spend on the ground is safe and well controlled. But all that moisture takes a toll on vulnerable magnesium, aluminum, and steel components. When it comes to the wheels, they are most susceptible to corrosion at the hub bearing bore. The wheel bearings are coated in grease, and protected from the elements by a felt disk sandwiched between thin steel shims. The felt is designed to be coated in grease and serve as a barrier to water making its way into the bearings. It’s an ancient design by any standard, made worse by the fact that it’s frequently neglected, left without grease or mistakenly coated in oil. Without proper maintenance, the felt acts as a sponge for water instead of a barrier to it. The result is predictable: more corrosion.

When the aircraft is parked, moisture that made its way into the bearings or hub will eat away at the bearing cups and cones, as well as the exposed aluminum (or magnesium) of the wheel itself. The bearing cups and cones are designed to be replaced and are fairly inexpensive. The wheel halves are a different story. If corrosion pitting on the wheel is allowed to progress unchecked, replacing a complete wheel assembly for a typical 6.00 x 6 main wheel can cost upward of $1,250. So, it pays to catch corrosion before it’s too late.

According to Vernon Rodgers, technical support training manager at Aircraft Wheel and Brake by Kaman (owners of Cleveland Wheels and Brakes), simple preventive maintenance tasks performed by an aircraft owner can help keep corrosion at bay and wheels and brakes in top condition. The FAA specifically allows aircraft owners to service landing gear wheel bearings. 

Additionally, owners can remove, install, and repair landing gear tires, which includes disassembly of the wheel itself. Performing these tasks will help protect wheels from moisture infiltration and corrosion. Cleveland offers technical data and manuals to supplement the aircraft manufacturer’s maintenance manuals. If you haven’t worked on your aircraft’s wheels before, be sure to have your A&P mechanic show you how to do it safely and properly.

In addition to improving maintenance practices, Cleveland recently introduced improved seals to help keep moisture out of the wheels and bearings. The new seals are made from a resilient rubber compound, molded to fit the inner and outer wheel halves. This new design eliminates the oil-soaked pad entirely and promises to streamline the maintenance process and improve wheel protection against the elements.

In addition to the wheels, the brakes have their own areas of corrosion concern, particularly the inside of the brake caliper. Hydraulic fluid is hygroscopic, meaning that it can absorb moisture from air that it is exposed to. Although most of the brake system is sealed, the reservoir is vented. If left long enough (typically many years), moisture can accumulate at the lowest point in the system and cause corrosion. Since the lowest point of most brake systems is the brake caliper, that translates into corrosion around the caliper piston bores and leaking brake fluid around the caliper pistons. The typical solution is to replace the piston O-rings, but when the corrosion gets extensive enough, the O-ring cannot effectively seal and the caliper will need to be replaced. The solution is to bleed the brakes every couple of years to ensure that the brake fluid remains clean and free of moisture. Bleeding the brakes is not considered preventive maintenance. However, with the proper tools, it’s fairly simple to do under the supervision of an A&P mechanic.

When it comes to aircraft wheels and brakes, a little preventive maintenance goes a long way to protecting your aircraft and your wallet. Best of all, the FAA has given you the authority to do much of the maintenance yourself. Until next time, I hope you and your families remain safe and healthy, and I wish you blue skies.