Airframe Technology: Kick the Tires and Light the Fire

Sept. 23, 2011
Maintenance practices include proper installation, inflation, and removal.

Kick the tires and light the fires - colorful maintenance jargon but poor advice concerning safety and the service life of aircraft tires. Recently during two long days of round-about travel, I had the opportunity to connect through diverse airports, experience some extremes in weather, and observe considerable ramp activity. From the boarding and airport observation lounges and a cabin seat, there appeared to be some less than stellar landings, several high-speed turnoffs, long taxi routes, 45-minute turnarounds, and some significant vibrations on rollout and takeoff. 

There were two takeaways from these casual observations. First, modern aircraft tires are dependable and capable of dealing with all of these extremes; second, tire gauges and service carts appeared missing from the scenarios. 

Aircraft tires are expensive, complex components that are vital to safe aircraft operations.  They are dependable and reliable but not indestructible. They require a significant amount of care and maintenance from owners, operators, and maintainers. Servicing tires should be as important as the check and replenishment of engine oils and hydraulic fluids. A good argument can be made that tires do not get the respect they deserve either on the ramp or in the classroom. The recommendations and requirements for tire care and preventive maintenance are straightforward and clearly stated in both OEM and FAA documentation. They provide advice and direction that should be the foundation of tire maintenance programs followed by all aircraft owners, operators, and maintainers.

Tire care and preventative maintenance

FAA Advisory Circular AC 65-15A (Chapter 9) and AC 20-97B dated 4/18/05, initiated by AFS-306, titled "Aircraft Tire Maintenance and Operational Practices" provides recommended tire care and maintenance practices needed to assure the safety of support personnel and the continued airworthiness of aircraft. Specifically, this AC provides guidance on the installation, inflation, maintenance, and removal of aircraft tires. In addition, it provides guidance on the operational practices necessary to maintain safe aircraft operations. The AC recommends that “operators should comply with tire inspection recommendations specified in the tire manufacturer’s CMM, and consult the tire inspection advice set forth in this document.”

Both the FAA Advisory Circular and the Goodyear Tire Care and Maintenance Manual stress tire preventative maintenance. Chapter Four: Preventative Maintenance in the Goodyear manual states that, “Tires cannot be taken for granted on any aircraft. Tire maintenance costs will be at their lowest and tire life will be at its longest if proper maintenance practices are observed. Safe tire operation also depends on proper maintenance. Thus, preventive tire maintenance leads to safer, more economical operations.”

They specifically address daily inspections and inflation checks. The AC states that “accurately maintaining the correct inflation pressure is the single-most effective task in the preventive maintenance regimen for safe tire operations.”  Both recommend that tire pressure should be checked daily or before the first flight with a calibrated gauge that is rated to read the pressure of the tires being checked.

OEM inflation procedures

Larry Rapsard, Goodyear’s North American aviation product support manager for GA Tires, agrees that the most important factor of any aircraft tire maintenance program is maintaining proper inflation pressure. His experience is considerable and as a Goodyear rep and Inspection Authorization (IA) renewal trainer, he’s seen and heard firsthand the detrimental effects of inadequate tire maintenance. Rapsard also recommends that aircraft tire inflation pressure should be checked daily because aircraft tires can lose up to 5 percent of their pressure each day.

Compensating for differences in temperature is one area where maintainers have room for improvement. For example, if pressure is checked in a warm hangar and then the aircraft is taken outside into a much colder condition and it sits for an hour or so before takeoff, tire pressure will drop. The temperature change should be considered when pressures are checked.

Which is more problematic - over- or underinflation?

Rapsard replies that “both over and under tire inflation have consequences. Under pressure can damage the tire and over pressure can stress the wheels and landing gears. Under inflation creates faster tread wear on the shoulders and increases the stress and flex resulting in excessive heating in the tire that can lead to tire failure.”

When asked which factors have the greatest influence on the service life of aircraft tire, he says, "Tire maintenance first and weather and taxi speeds next. High taxi speeds and especially high speed turns can really stress and wear the tires.”

Asked if he had any training tips or recommendations for other AMTs, he recommended that they always follow the Goodyear Tire Care and Maintenance Manual and call with any questions and concerns about Goodyear Aviation Tires. He also shared his list of tire tips that he includes in his IA renewal training (see sidebar).

If you access the Goodyear Aviation Tire home page at http://www.goodyearaviation.com/resources/training.html and click on the Technical Resources tab you will find two excellent training videos. 

1. "Aircraft Tire & Maintenance Training - Tire Types, Reading a Sidewall & Proper Mounting & Inflation." In this video, the bias and radial tire construction is reviewed, along with reading an aviation tire sidewall. Proper mounting and inflation techniques are discussed.

2. "Aircraft Tire & Maintenance Training - Operating Conditions and In-Service Inspections."
In this video, the effects of operating conditions such as centrifugal force, heat, and inflation are reviewed. Additionally in-service inspections on inflation, wear, damage, and demounting tires are discussed. 

Tire care and maintenance in business aviation

It is always interesting to learn how the aircraft OEMs support their customers and staff. I asked Gulfstream Aerospace Corp. if it would give its perspective on tire care and maintenance. A team of professionals that included Mark Fulkerson, technical specialist II; and Fred Karst, director - services engineering, provided a quick response to my request for information.

According to the Gulfstream team, “Tire service life in general is trending up. Increased attention to maintenance, and the manufacturers’ dedication to improve tire tread compounds and manufacturing processes, have resulted in an increase in the number of landings per tire. A vast majority of “early removals” are due to FOD, not tire wear. The increased awareness to proper care and maintenance seems to really be paying dividends for everyone.”

When asked about tire care and maintenance training for its customers and staff, it partners with FlightSafety International for both customer and staff training. FlightSafety’s Total Technical Training is an aircraft systems training program for all Gulfstream aircraft delivered at its joint Maintenance Training Center in Savannah, GA.

New maintenance issues 

Asked if Gulfstream is seeing any new problems arising from the field in the tire care and maintenance area, they stated a concern about some of the current tire cleaning practices. “Everyone likes to see shiny new looking tires on their Gulfstream. The problem is with some of the chemicals used to make them shine. The harsher cleaners actually remove waxes and oils from the outer surface of the tire, which help protect the rubber from ozone attack. In addition, these products are usually applied heavily and by spraying. The overspray can lead to corrosion on the landing gear, wheels and brakes, even affecting braking performance.”

The final recommendation from the Gulfstream team was that we remember that underinflation is the No. 1 tire maintenance issue and it's 100 percent avoidable. They presented a seven-step job-aid to help with this issue (See related copy).

The message from the FAA, Goodyear’s North American Aviation group and Gulfstream Aerospace Corporation on aircraft tire care and maintenance is clear, don’t just kick the tires, service them. If you want a safe tire and a long service life for your aircraft tires, simply check pressure frequently and keep tires inflated to the appropriate pressure.

Field Editor Charles Chandler has a Masters of Science Degree in Adult and Occupational Education with a major in Human Resources Development. He began his aviation career as a junior mechanic for American Airlines and retired after 27 years of service. After leaving American he held both line and staff positions in six other major companies. His positions with those companies included curriculum development specialist, manager and director for organizational development, management and leadership development, and maintenance training operations departments.