# Aircraft Wheels and Tyres: Inspection, Wear, and Thermal Protection

> Tyre wear patterns, pre-flight rejection criteria, contamination risks, and fusible-plug thermal protection in aircraft wheel assemblies.

- **Subject:** 021 — Airframe, Systems, Electrics, Powerplant
- **Section:** 021-04 — Landing Gear, Wheels, Tyres, Brakes
- **Topic code:** 021-04-04
- **Last reviewed:** 2026-03-27
- **Author:** Pablo Asensio Martínez
- **HTML version:** https://pilotsyllabus.com/en/airframe-systems-electrics-powerplant/landing-gear-wheels-tyres-brakes/wheels-rims-and-tyres/

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Aircraft tyres are critical components designed to withstand short-duration, high-speed loads during take-off and landing. Proper maintenance and pre-flight inspections are essential to prevent failures such as bursts or blow-outs.

## Tyre Characteristics and Wear

- **Design:** Tyres are built for intermittent high loads, not continuous long-distance rolling like car tyres.
- **Taxi Speed:** High taxi speeds can cause excessive heat and damage. The recommended taxi speed is generally around **20 KTS**.
- **Pressure Effects:**
    - **Low Pressure:** Causes excessive wear on the **shoulders** of the tyre.
    - **High Pressure:** Causes excessive wear on the **crown** (center) of the tyre.

## Pre-Flight Inspection

Pilots must verify the condition of the tyres before flight. Operating with damaged tyres can lead to bursts and airframe damage.

- **Cuts:** Deep cuts that penetrate to the cords or ply render the tyre unserviceable.
- **Bulges:** Indicate a partial **failure of the casing** or internal structure.
- **Foreign Bodies:** Stones, metal, or glass embedded in the tyre **must NOT be removed** by the pilot. They should be reported to maintenance staff for proper assessment.
- **Wear Limits:** Tyres must not be used if the tread is worn beyond specific limits (e.g., to the base of marker grooves).
- **Creep:** Signs of movement of the tyre around the wheel rim. Exceeding creep limits (e.g., 1 to 1.5 inches depending on diameter) requires removal and inspection of the tube/valve.
- **Contamination:** **Oil, fuel, or hydraulic fluid** on the tyre surface can degrade the rubber.
- **Blisters:** A blister indicates that the **plies of the carcass are delaminating**, requiring tyre replacement.
- **Tread Separation:** Occurs when the rubber tread separates from the inner layers. This reduces traction, causes vibration, and often leads to a **tyre blow-out**.

## Safety Features: Fusible Plugs

To prevent catastrophic tyre bursts due to overheating, aircraft wheels are equipped with safety devices.

- **Fusible (Thermal) Plugs:**
    - **Location:** Installed in the **wheel hub**.
    - **Function:** Designed to melt at a specific **excessive temperature**.
    - **Purpose:** Heavy braking (especially after a Rejected Take-Off) generates immense heat, increasing tyre pressure dangerously. The plug melts to allow **controlled deflation** of the tyre, preventing an explosive burst that could damage the aircraft or engine.

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Free study notes from pilotsyllabus.com. Not a substitute for training at an approved ATO.