Aircraft Tyres — Page 129, Lesson 171

Let’s pick up right where the tyre chapter leaves off, because this is the part that ties the whole tyre story together — what happens when things go wrong, and how we protect the tyres so they last. First, the failure modes. A tyre can burst, or the treaded portion — that’s the rubber layer with the grooves that contacts the ground — can become detached from the tyre body. Either way, the result is the same kind of problem. With less tread or a burst tyre, the contact patch, what we call the footprint, gets smaller. That means the remaining tyres on the aircraft now have to carry more load, so the loading on them increases. And because you’ve lost part of the braking surface, braking efficiency goes down. So you have a smaller footprint, increased loading on the remaining tyres, and reduced braking efficiency — all three consequences follow from that one failure. There’s also a safety hazard beyond just the tyre itself. This is where we bring in foreign object damage, FOD. If the tread detaches or the tyre bursts, debris can be thrown around. That debris can damage the brake hydraulic lines, and it can be ingested into the engine. So FOD isn’t just about the tyre — it’s a threat to the braking system and to the powerplant. Now, how do we reduce tyre wear in the first place? The key factor here is taxi distance. Modern airports are bigger, so taxi distances are longer, and that means more rolling, more wear, and more risk of damage. The recommendation to minimise that wear is to keep taxi speed to no more than 25 mph, which is 40 kph. That’s the limit you should not exceed during taxi. Then there’s inflation pressure, and this is a classic cause-and-effect pair you need to hold onto. Over-inflation causes excessive wear to the crown of the tyre — the crown is the centre of the tread, the part that bulges out when the tyre is over-pressurised, so it takes the brunt of the contact. Under-inflation does the opposite: it causes excessive shoulder wear. The shoulders are the edges of the tread, where the tyre flexes more when it’s soft. So remember the contrast — over-inflation wears the crown, under-inflation wears the shoulders. And that brings us to the figure on the page, Figure 5.3, which shows wear markers and indicating grooves. These are the built-in indicators on the tyre that let you see, at a glance, how much tread is left. The wear markers are small raised bars in the tread grooves, and the indicating grooves are the channels cut into the tread. When the tread wears down to the level of the wear markers, you know the tyre has reached its wear limit and needs attention. That’s your visual check for tread depth. So, to tie it all together: a burst or tread detachment shrinks the footprint, overloads the remaining tyres, cuts braking efficiency, and risks FOD to the brake lines and engine. To prevent wear, keep taxi speed at or below 25 mph / 40 kph. And watch your inflation — over-inflation wears the crown, under-inflation wears the shoulders — with the wear markers and indicating grooves in Figure 5.3 as your visual cue for tread condition.