IT WAS A SUNNY morning in March when the pilot of a Cessna 177 Cardinal turned final for Runway 35 at Concord Municipal Airport in Concord, New Hampshire. The winds were light, visibility was unrestricted, and the temperature hovered around 18°F. The runways were clear and dry, and no other traffic was in the pattern. What could possibly go wrong?
Touching down, the pilot held back on the elevator and allowed the aerodynamic drag to slow the aircraft; there was no need to use the brakes. As the aircraft approached the intersection, the pilot pushed the left rudder and gently tapped the left brake to exit the runway, and then taxied briskly to the ramp in front of the FBO. It seemed that the flight would finish without a hitch, but such was not the case. The surprise came when the pilot tapped the right brake to maneuver the aircraft for parking—nothing. The pedal was firm, but totally ineffective. The pilot jammed on the rudder to maneuver the aircraft and pulled the mixture out to shut down the engine as the wingtip narrowly missed another aircraft on the ramp. Fortunately, the aircraft came to rest without colliding with anything. The pilot scratched his head, wondering what had gone wrong, and what he missed on his pre-T ‘ flight inspection.
Brakes are often taken for granted. Sure, we check them on preflight, and test them before taxiing, but seldom do we find problems. So when a problem does arise, it usually takes us by surprise, setting us up for some serious damage. Considering the consequences of not stopping when necessary, it pays to give our brakes some thoughtful consideration, not only during the preflight, but at various key points in flight.
Perhaps the most obvious sign of brake trouble is a puddle of hydraulic fluid near the wheels, but not all leaks occur near the calipers. A slippery feel to the floor mats is a sure sign that a hydraulic brake cylinder has developed a leak near the rudder pedals. Likewise, pilots should carefully examine within the cowl and beneath it for the telltale signs of a leaking cylinder or hydraulic fluid reservoir.
If possible when checking the brakes, we should examine the brake pads and rotors. On most aircraft, the pads should be no thinner than a quarter. Any thinner than this, and the rivet head that holds the pads in place will begin to rub on the rotor. The rotor should be smooth, and not grooved or gouged.
Before starting the engine, we should test the brakes to make certain they don’t feel “spongy,” as this is a sign of air in the brake lines, possibly caused by a leak.
One very important performance parameter is landing distance. Of particular concern is the ground roll, which is based on our ability to brake effectively. While we seldom consider this in much detail, several factors affect our ability to stop a rolling aircraft on the ground. First, consider that the brakes themselves must be working properly. Brakes that have just been used and are hot may not provide the braking capacity needed to meet the published performance data. While this is seldom an issue with light training aircraft, it can be a major consideration in heavier and high-performance aircraft.
Next is the friction between the tires and the surface. In general, braking performance, and thus stopping distance, is based on the tires being in full contact with dry pavement. Any contamination of the surface such as water, ice, snow, or sand can reduce braking effectiveness considerably. Other landing surfaces such as gravel or grass will not provide the same braking effectiveness as dry pavement. Naturally, the condition of the tire itself—proper inflation and tread condition—also is important to braking.
Optimum braking performance also requires the weight of the aircraft to be on the landing gear. If the wings are generating lift, the weight on the landing gear is reduced and the friction between the tires and the surface will be diminished. The end result can be significantly increased stopping distances.
TIPS AND TECHNIQUES
The acid test for brake function comes when we apply brakes shortly after the aircraft begins to move. Before taxiing more than an aircraft length, we should test the brakes to verify that they are indeed working. But don’t make the mistake of assuming that just because the brakes worked last time that they’re going to work again. A good practice is to always test the brakes before we need them, and always have a plan in mind for what to do if they don’t work. Given enough space and time, we can often maneuver the aircraft away from obstacles. The key to success is to avoid excess speed, which increases the space and time required to successfully maneuver out of harm’s way.
After liftoff, tap the brakes to stop the wheels from spinning. Stopping them in a random position this way can help prevent a flat spot caused by the tire always touching pavement on the same spot. For retractable gear aircraft, stopping the wheels before gear retraction also reduces the potential of the wheel becoming jammed in the wheel well. Before landing, test the brakes to see that they feel firm. If not, be prepared for trouble after touchdown, and plan your landing accordingly.
To improve braking, look for surface conditions that could affect tire friction. Ice and snow on runways and taxiways are a clear indication of diminished braking capability. As we move into spring, remember that melting snow and ice will often refreeze when the sun goes down and temperatures drop, so look for that sheen that indicates an ice-covered surface. On taxiways and runways, we might do better to keep our tires on the dry pavement, even if it means deviating from the centerline. Just be certain to have the necessary wingtip clearance for any obstacles. Also, be aware of windy conditions when braking action is reduced, as the combination can quickly get us off track and off the pavement.
Early morning dew or frost on grass can turn a turf runway into a virtual skating rink in terms of braking ability. Once again, if we give those brakes a gentle tap, we can quickly ascertain the degree to which they will serve us.
Few light aircraft are equipped with anti-skid braking, so remember that on a slick surface, it can be more effective to pump the brakes (press and release repeatedly) rather than just maintaining pressure on the brakes when the wheels lock. This will help prevent a skid and improve our ability to maintain directional control.
Later that morning, the pilot of the Cessna 177 learned the cause of his brake problem. It turns out that the hydraulic fluid in the left brake line had been contaminated with moisture, which had accumulated and then frozen in the cold temperatures, completely blocking the hydraulic line. Depressing the pedal pressurized the hydraulic line only up to the ice plug. No pressure reached the calipers, rendering the brake totally ineffective. Luckily, the fix was neither costly nor time-consuming. Had he run into another aircraft or obstacle on the ramp, the result would have been much different.
Of the many risks we face while flying, that of a brake failure might be relatively rare, but the consequences can still be serious. By maintaining awareness and adopting safe operating strategies, we can avoid the pitfalls that put the brakes on our flying.