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Them’s the Brakes
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By John Lorenz
The setting: taxiing downhill on a sloping runway, with a good tailwind and with partial throttle. At 800 ft from the end of the runway, we pulled the throttle back, but gravity and the wind kept us moving along at a pretty good clip. At 400 ft from the end of the runway, we started to apply brakes and discovered to our consternation that the right pedal went cheerfully to the floor with absolutely no effect. Stabs at the left brake established that whereas by itself it might be capable of pulling us sideways off the runway, judicious use of it while trying to stay on the runway wasn’t even beginning to slow us down. We were about to over-run the end of the runway, where for years a barbed-wire fence had kept cows from wandering onto the airport. A quick mental run-through of the options came up with several less-than-helpful ideas: 1) veer left off into the rough, risking a prop strike on the runway-edge lights or in the rough terrain; 2) ground loop to the left, risking tipping the plane over, but the left brake probably wasn’t strong enough to do that anyway, or 3) plow head-on into the fence.
We had taxied uphill from the hangar, not needing brakes, and then proceeded at a fast taxi on the runway towards the run-up area, still not feeling the need for brakes. The lack of brakes that was now obvious could have bitten us several times earlier if we had been trying to maneuver among parked aircraft, or perhaps during the run-up. We hadn’t asked the brake system whether it worked or not, but it was going to tell us sooner or later.
As we sailed off the end of the runway, I thought stupidly that it was one of the few times I hadn’t checked the brakes after beginning to taxi, and that we really should have known that taxiing that fast in those conditions wasn’t good form.
Experience is a hell of an instructor. It doesn’t care whether or not you did your homework. Here’s the test; there are no makeup exams, and quit yer whining. Today’s lesson is "check the brakes when you first pull out from the chocks, when the aircraft can be shut down before getting into a situation where the lack of brakes is going to be embarrassing." The corollary is "don’t taxi fast downhill with a tailwind."
Later inspection showed that brake fluid must have been slowly leaking out of the right wheel brake cylinder, so slowly that there wasn’t even the expected puddle of red hydraulic fluid on the floor where the aircraft was parked. I don’t know where it went, it had just seemed to de-materialize, as the brake line on that side was devoid of fluid. Much of it had probably been left on another ramp where the plane had been parked during the previous week.
Pilots often think of aircraft brakes in the same terms as brakes on the family Ford, but there are some important differences. For one, aircraft systems develop leaks more often, and shouldn’t be taken for granted. For another, aircraft shouldn’t be braked hard while turning at high speed, as when trying to make an early turnoff from the runway after a landing. The tricycle configuration of the wheels makes aircraft prone to tipping during a braked turn. Rather, brake while tracking straight ahead, and make the turn only after decelerating to taxi speed; accept a 180 turn back to the turnoff or go on to the next one if necessary.
Even when working well, aircraft braking capacity isn’t wonderful. If you need to slow the taxi speed of an aircraft, the first reaction should be to pull the throttle back, and then add brakes. Otherwise, it’s like pushing the accelerator and brake pedals at the same time in a car. Brakes are there for slow taxiing, tight turns, and run-ups, and shouldn’t be abused during high-speed taxis or regular short-field landings. Sure, aircraft brakes in good condition will lock up a wheel in an emergency, but aircraft tires are so small that even locking up a wheel doesn’t provide much stopping power. If the aircraft has speed when the brakes are locked, it just leaves bald spots on the tires and interesting black lines on the pavement. If high-speed braking is continued, it blows out the tire, and that adds serious steering difficulties to the shortening-runway-remaining problem. Brakes are a last resort for short runways or downwind landings — better planning is the preferred option.
Even if the tires don’t blow, older types of brakes can fade and become less effective as they heat up. Heat can also do more direct damage: one pilot of a homebuilt with a castering nosewheel had to ride the downwind brake in order to stay on the taxiway during extended taxi in a crosswind. The brake fluid heated up and caught fire, resulting in major damage to the flammable, composite aircraft.
As luck would have it, the barbed wire fence at the end of our runway had recently been taken down. We overran the end of the runway and sailed – chagrined but undamaged – onto the gravel beyond. Sometimes you get away with one. |
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