Where the rubber meets the ramp
Tips for preflight tire inspection
Pilots almost always look closely at the tires on an aircraft. After all, some expensive machinery rests upon three relatively small footprints. Surprisingly, the criteria for determining acceptable tire wear or damage is not well known. Let's examine the common problem areas and discuss ways in which you and your students can determine whether a tire is safe, merely acceptable, or needs to go to the tire graveyard.
Aviation tires are manufactured to high standards and have a very low incidence of outright failure. According to Goodyear's Aircraft Tire Care and Maintenance Manual, some exotic inspection techniques exist to ensure that no bad eggs find their way to your landing gear. Unfortunately, once tires are mounted and we begin inflicting aviation on them, we are back to using our eyeballs to determine whether they are airworthy. Tire kicking makes us feel better, but offers no real information as to tire condition. You must visually inspect tires and make a judgment call. Even then, your students might want to ask for a second opinion, and postsolo students should be encouraged to ask an instructor or mechanic to help them check a tire's airworthiness if there's any question.
The most common concern areas are improper inflation, worn tread, scuffs, weather checking, bulges, and cuts. So where or how do we draw the line? The following tips are what the leading tire manufacturers recommend.
Inflation problems dramatically reduce tire life. Even a slight amount of over- or underinflation will accelerate wear and increase stress to the tire. A lightweight digital or dial-type tire gauge is a handy addition to your flight bag and is a much more scientific method than trying to guess whether the tire "looks a little low." Don't forget temperature effects. If the last time you checked pressure was August, you can be sure it won't be right on winter's first frosty morning. Inflate for the coolest temperature, and remember that even a few degrees' difference will change your tire pressure. Improper air pressure is a big service-life killer and can be a safety of flight item on the preflight checklist. Inattention will certainly lead to uneven tread wear.
When you see wear patterns on the center or edge of the tire, it's a signal to keep better tabs on pressure-but what is acceptable once the pattern appears?
In general, if the tread groove depth is no longer visible, the tire should be removed and replaced. If you wouldn't want it on the family car, don't try to squeeze a few more touch and goes out of it on the Cessna.
Scuffs are the oval flat spots from normal landings or a slightly heavy foot on your last short-field demo. Almost every pilot has scuffed a tire. Unless wheel balance is unacceptable, scuffs aren't generally considered troublesome until the groove/tread patterns are eliminated. If fabric shows anywhere in the scuff, however, the tire is ruined. Otherwise, minor scuffs are tolerable.
Weather checking on sidewalls is the crack pattern that occurs because of age and exposure to the elements. Although meticulous aircraft owners will fret over the appearance, the tires won't be a problem provided no cord fabric shows through. Fabric on the sidewall means retirement for the aged tire.
Bulges, raised areas, or blisters indicate serious internal problems with the tire's carcass and tread. Things are already coming apart inside the tire, so matters can only get worse if you subject it to high speed and normal stress. A visible bulge is a definite grounding item and flying on it could result in a failure. Don't chance it; replace it as soon as possible.
Cuts will occur during normal use. High-traction grooved runways can be rough on the tread, especially during crosswind or landings with side loads. Some tires have the cut limits published either in the technical orders, operating manual, or on the side of the tire. In the absence of specific guidance, a good rule of thumb is to remove the tire if any cut penetrates to fabric. The Goodyear manual urges pilots to use caution when investigating cuts or embedded foreign objects. Don't start exploratory surgery on a mounted tire still under pressure-that's a good way to get hurt.
These wear and tear scenarios are the more common areas that pilots have questions about. Some pilots will fly with the thinnest of margins while others will want new rubber when useful life still remains. With these inspection techniques you can offer your students some guidelines to help gauge where the safety margins begin and end. Good preflight techniques can reduce their chances of ever experiencing a tire failure during takeoff or landing.
Dave Hensley is manager of standards and curriculum at Regional Airline Academy in DeLand, Florida. A former Air Force U-2 pilot, he is an aviation safety counselor, a Master CFI, and a Civil Air Patrol check pilot. He has more than 7,600 flight hours.
By Dave Hensley