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