When one thinks of all the things that an aircraft can do, stopping is not one of those things that immediately jump to mind. Given that aircraft manufacturers don’t equip their products with ventilated brake discs, twin calipers, or carbon-metallic brake pads, it’s no surprise that braking an aircraft to a standstill is that part of a flight that draws little in way of attention. But, there are always better ways of doing things, and aircraft braking technique is one of those things.
Riding the brakes while taxiing, or being forced to use the brakes as a means to control excessive speed while venturing to, or from, a runway, will wear the brakes out. Landing an airplane too fast, and being forced to brake excessively hard to stop the airplane’s momentum, will shorten brake life too.
Braking shouldn’t begin the moment the wheels touch down. Since the airplane, at this stage of the landing, is still producing some lift, applying the brakes won’t have much effect on slowing the airplane down. In fact, aerodynamic drag will provide greater deceleration of the aircraft than will braking, in the first quarter of the aircraft’s slowing down process. Lowering a nosewheel aircraft’s front wheel quickly to the runway reduces wing lift. The quicker the wing lift is eliminated, the more effective the brakes will become. Braking effects rise when the aircraft’s airspeed and lift fall. When slowed to approximately 75 percent of its initial touchdown speed, an aircraft will roll to an eventual stop owing to a combination of rolling friction and braking power.
When touched down, the throttle should be completely closed to ensure that power is not counteracting the pilot’s attempts to stop. Brakes should be applied smoothly, firmly and without modulation. Weight on the main landing gear makes for the most effective braking. Back pressure on the control column forces the aircraft’s weight onto the main gear, by keeping less weight on the nosewheel. Backpressure on the latter, however, should not be too great, as the nosewheel is needed to steer the airplane.
Pumping the brakes should be avoided. If brake application is intermittent such that the brakes, between successive applications, are not allowed sufficient time to cool, excessive heat energy is created. If not allowed to cool, residual energy in the insufficiently cooled brake disc is added to the heat energy created from the next brake application. The resultant high temperature can exceed the brake system’s insulation threshold, and boil the brake fluid in the brake master cylinders. When this happens, the brake pedal travel gets long, and braking pressure becomes less effective.
While braking, care must be taken to avoid the locking of wheels. A sliding or skidding tire doesn’t brake as well as a rolling one. An uneven runway surface, coupled with high and constant brake pressure from the pilot, can cause an unloaded wheel to lock up, thus lengthening the landing distance. Longer still will be the landing on a wet, snow-covered, or icy runway. Brakes, in the latter circumstances, may not be of much use at all.
Using appropriate speeds during taxiing and landing best avoids brake problems. Proper care of the brake system will avoid problems too. Moisture, salt and industrial chemicals can cause corrosion on brake discs. Aircraft that sit unused for long periods of time are particularly susceptible to such contamination.
Brake fluids must be carefully monitored both for appropriate levels and proper type. While the fluid serves to transmit pressure and energy for stopping power, it also serves as a lubricant and cools moving parts in the brake system. Mixing of inappropriate fluids can render a brake system totally ineffective. Furthermore, the wrong fluid introduced into a brake system can actually dissolve its rubber seals.
Finally, brake fluid must be clean. Dirt in the system can make it inoperable.