Airframe Technology: Proper Tire Selection & Maintenance

They’re round, black, and made of rubber. Tires may not seem, at first glance, like amazing feats of technological advancement when compared to the computer systems, engines, and other complex components of the modern aircraft. However, the research and testing, along with significant technology in manufacturing, make any plane’s tires as equally complex as most other components. As much as engines, navigation instruments, and other components allow flight to safely take place, without well-maintained tires, planes wouldn’t be able to leave or return to the ground safely.

Overall aviation safety depends heavily on the reliability and performance of the aircraft’s tires. Tires have been drawing more attention in the aviation industry following a Sept. 19, 2008, Lear jet crash in Columbia, SC, where underinflated tires were determined to be partially at fault.

Proper selection and maintenance of tires will greatly increase the safety of tire performance on any aircraft. An excellent way to ensure tire safety is through a tire management program. Every aircraft or fleet maintenance team should have a tire management and maintenance program in place. That tire program should be written; communicated to all technicians and maintenance staff; monitored for efficiency, proper execution, and possible modification; and then enforced to ensure the quality and safety of every tire on every aircraft. A maintenance shop should provide each plane‘s tires with the proper care needed to ensure the tires will be able to safely perform during takeoff and landing.

Maintaining proper tire pressure

The first — and the most critical — element of a tire maintenance program is maintaining correct tire pressure. Even if an aircraft has been fitted with an appropriately selected tire, the tire must have proper tire pressure to operate safely. If maintenance personnel do only one thing in the way of tire management, maintaining the correct air pressure in each tire is that fundamental requirement. Tires are designed and manufactured to be operated at a specific air pressure for the particular load. Tires that are maintained at the proper pressure will perform better and safer, and last longer than under- or overinflated tires. When proper tire pressure is not maintained, the safety of that tire diminishes.

In the case of the 2008 Lear jet crash, the NTSB reported that subsequent tests showed the tires to be underinflated by approximately 36 percent. The aircraft maintenance manual called for a tire to be replaced if it was operated at a pressure difference of 15 percent or more.

When a tire runs underinflated, the tire deflects at a higher rate, causing the heat that a tire generates while rolling to increase significantly. This excessive flexing of the tire can weaken the casing plies and increase the internal temperature of the tire and its rubber. High temperatures are capable of degrading the rubber (rubber reversion) and of melting the tire cord. This can cause the tire to fail.

Understanding tire construction

Another basic understanding in tire management is the types of tires. As radial tires become more common and gain more certifications, maintenance teams should understand how they operate as well as consider the benefits of radial tires, which were introduced to the aviation industry by Michelin in 1981. While bias-ply aircraft tires continue to improve in their technology and safety, radial tires provide several advantages. Radial tires have roughly twice the heat dissipation as bias-ply tires. Heat buildup is what can lead a tire to fail. Not only do radial tires run cooler, but the reinforced contact patch delivers less squirming throughout the tread area, which leads to longer life — as much as 50 to 100 percent longer than bias-ply tires.

Choosing the right tire is also key to retreading the tire, which can bring significant cost savings. Whether fitting radial or bias-ply tires, the better a tire’s initial quality, the better chance its casing will qualify for and withstand the retreading process. Retreading is a very important part of aviation tires. Retreads are not only cheaper than a new tire but are also just as good as the new tire and better for the environment, with fewer raw materials used to make a retread than a new tire.

Partnering with a trusted service provider

While most fleets already have some system in place, with a little help and a few improvements, a fleet can further increase the safety of its aircrafts’ tires. For that reason, some manufacturers, like Michelin, provide a technical sales force armed with helpful insight and capable of partnering and counseling fleets on their tire needs and maintenance practices.

By helping the industry properly care for and maintain its tires, tire makers are able to contribute to increased aircraft safety. Michelin, for example, also offers authorized service centers, which can provide a variety of maintenance training and service. Value-added services like these can help reduce direct maintenance costs and increase tire performance and safety.

If maintenance staff do not feel adequately trained or knowledgeable about the proper selection and maintenance of aircraft tires, training courses are available. The goal of these programs is to help maintenance managers and personnel prepare the aircraft to achieve optimum performance and safety.

Aircraft maintenance personnel are responsible for the reliable performance of the aircraft — including its tires. Time spent to properly understand tire management and maintenance will pay off in terms of increased performance, and ultimately, increased safety. AMT

Keat Pruszenski is the customer engineering support manager for Michelin Aircraft Tire Company, a division of Michelin North America. A graduate of the University of Mississippi in engineering, Pruszenski has been in his current role for eight years. He has logged more than 2,500 hours of flight time and enjoys flying his two planes (Quicksilver GT 400 and Piper Cherokee 160) as a resident of Chandelle Flight Park. Pruszenski is a member of the SC Aviation Safety Council, as well as AOPA.