action by the flight crew can reduce the likelihood of brake
overheating and concomitant departure delays.
When a twin-aisle airplane
is used for short-flight operations, brakes may heat unevenly on
each landing, with the difference in temperatures becoming more
pronounced with repeated landings. At the gate, the brake temperature
display may indicate that some brakes are hotter than others. Temperatures
may continue to climb until the brake temperature light illuminates
or an alert displays. Understanding the causes of uneven brake heating
and the meaning of the brake temperature indication can help flight
crews minimize possible departure delays. This article explains
that lead to uneven brake heating.
of the brake temperature indication.
crew action that can minimize uneven brake heating.
FACTORS THAT LEAD TO UNEVEN BRAKE HEATING
Slowing an airplane requires
the dissipation of kinetic energy. Kinetic energy that is not absorbed
by the thrust reversers and speed brakes is converted to heat energy
by the wheel brakes. The weight and speed of the airplane during
landing and taxiing determine how much energy the brake friction
(i.e., heat stack) material absorbs.
Factors that lead to
uneven brake heating include variation in brake wear, inadvertent
asymmetrical braking, and wind conditions.
in brake wear.
Brakes that are approaching wear limits can become as much as 30
percent hotter than unworn brakes. This variation in temperature
simply reflects the difference in the amount of brake friction material.
Temperature differences between brakes on the left and right gears
often arise from inadvertent asymmetrical braking. When the brakes
and rudder pedals are used concurrently to maintain heading and
keep speed under control, it is easy for flight crews to inadvertently
apply asymmetrical braking inputs that unknown to them
are being compensated for by the rudder. When the pedal brakes are
applied lightly during taxi braking and landings, temperature differences
among the brakes on each landing gear can increase quickly.