Tyres, braking, anti-skid and autobrake

Track where the aircraft’s kinetic energy goes

Relate aircraft mass and speed to kinetic energy, then distinguish brake-energy, tyre-speed and heat-transfer limits.

Mechanism and relationships

Wheel brakes create a retarding torque and convert a share of aircraft kinetic energy into heat in the brake assemblies. Aerodynamic drag, reverse thrust and rolling resistance can absorb other shares. The total kinetic energy is ½mv², so a modest increase in speed can add substantial braking energy. Carbon and steel brakes have different material behaviour, wear characteristics and temperature responses. The indicated temperature may lag the hottest internal components because heat must travel to the sensor.

Reason through the evidence

Tyres support load through their construction and inflation pressure while tolerating rotation and heating. A tyre-speed limitation is different from a brake-energy limitation. Heat from brakes can transfer to the wheel and tyre after stopping; pressure-relief devices protect against specified overpressure mechanisms but are not a guarantee that approaching a hot wheel is safe. Use the aircraft cooling and inspection data rather than equating an illustrative sensor temperature with a release threshold.

Apply the explanation to a different case

Compare two identical-mass landings that begin wheel braking at 60 and 66 m/s. Their kinetic-energy ratio is 1.21 before assigning any work to drag or reverse thrust. Even if a deceleration setting feels the same, the faster case has more total energy to remove. A longer application can also change the distribution of heat through the brake stack and sensor. Brake wear, thermal capacity and tyre speed are separate constraints; satisfying one does not establish the others. This is why a single temperature number cannot replace the aircraft’s brake-energy and cooling data.

Keep this distinction clear

Brake torque produces tyre force only while the tyre can transmit that force to the surface. Increasing torque beyond the useful friction region can lock or excessively slip a wheel. More hydraulic pressure is therefore not equivalent to more aircraft deceleration under every surface condition.

Distinguish wheel-slip control from deceleration control

Distinguish anti-skid wheel-slip control from autobrake deceleration control and explain how other retarding forces change brake demand.

Mechanism and relationships

Anti-skid monitors wheel behaviour and modulates brake pressure to avoid excessive slip or a locked wheel. It cannot create runway friction. Autobrake compares measured aircraft deceleration with a selected target and commands brake pressure within available authority. If reverse thrust or aerodynamic drag supplies more deceleration, less wheel-brake force may be needed to meet the same target. If friction is insufficient, the target may remain unmet even with strong braking demand.

Reason through the evidence

A wheel-speed signal, an aircraft deceleration estimate and an available pressure source perform different roles. Anti-skid can limit the pressure that an autobrake loop requests. The frequently taught square-root tyre-pressure formula is an approximate dynamic-hydroplaning relationship under stated conditions, not a lower-speed safety guarantee: viscous and reverted-rubber mechanisms differ. The lab instead uses explicitly synthetic friction-versus-slip curves to make the feedback purpose visible.

Apply the explanation to a different case

Imagine that an autobrake requests enough pressure for its target, but one wheel begins excessive slip on a low-friction patch. Anti-skid can release or limit that wheel’s pressure even while the deceleration controller would prefer more braking. The two loops have different controlled variables and their interaction is intentional. A continuing deceleration shortfall does not prove that the autobrake forgot its target; the requested force may be physically unavailable. Plotting a synthetic friction-versus-slip curve makes this limit visible without claiming that the curve predicts any real wet or contaminated runway.

Keep this distinction clear

Autobrake disarm logic, pedal override and touchdown requirements differ between installations. A selected deceleration label does not prove that the system is armed, active or still engaged. These are separate states with their own indication and input conditions, just like other closed-loop systems.

Can you explain and apply the mechanism?

Four original questions. Work from the stated facts, then compare your reasoning with the explanation.