Unskilled taxiing will damage a pilot's aircraft and pride. While most aircraft fly well, few handle as well on the ground. Certainly no aircraft is as agile as the automobiles we drive.
This is because of compromises in aircraft design. We want our aircraft to fly well, and taxiing is incidental to the goals of aircraft designers. My initial flying lessons were at an airport with an 11,000-foot runway, which meant taxiing two miles before I could take off. It was all I could do to keep the aircraft under control during this lengthy trip. During my first lesson I reached the end of the runway after major weaving. Exhausted from the effort, I strongly considered asking my instructor if we could taxi back for more practice. I was overwhelmed with the difficulties and could not imagine I would master flying the Cessna 150. How things change -- but safe taxiing still requires undivided attention.
Taxi planning must begin when we first approach the aircraft. If you remove chocks, where do you put them? It is tempting to place them behind the wheels, but in most cases you should spend the few minutes to carry them off the parking ramp so that the next taxiing aircraft will not run into them.
Removing chocks in front of each wheel and leaving them behind wheels is a necessity when the aircraft might roll backward on uneven ground. However, it is best not to leave a chock behind the nosewheel. If you turn sharply, a main gear may meet the chock, bringing aircraft motion to an uncomfortable and unexpected stop.
The most obvious error is forgetting to untie aircraft. There is probably no seasoned pilot who has not done this once. It is embarrassing to gun the engine and feel the aircraft strain, but not move an inch because the tail is still fastened to the ground. But it is even more embarrassing when your aircraft begins to circle about a point because of a tied wing.
While chock and tiedown omissions may be comical, they usually are not as damaging as failing to look about the aircraft as you do a walk-around. Assess all nearby objects on the ground, in particular nearby props, wings, and tails. Aircraft are irregularly shaped and fragile objects. The objective is to get the aircraft to the runway without damaging it or anything else on the tarmac. This means when walking around the aircraft, survey the surroundings -- what I call "looking outside the circle."
Unlike automobiles, aircraft turn axes are well forward and vary. Thus, when tightly turning an aircraft -- with a combination of sharp nosewheel steering and braking the inside main gear -- unexpected things happen. If you lock a main gear, the axis of the turn will be about that wheel. That means the wing outboard of that gear will move backward as you turn. Is there anything in the way as that wing retreats? Even less-vigorous turns can slew the tail to the outside of the turn.
Unexpected tail wagging can impact another aircraft. Therefore, in your walk-around you must determine if an immediate sharp turn is required, and if so, will contrary motion of a wing tip or tail clear surrounding obstacles? Often aircraft are parked wing tip to wing tip, or they are taxied to parking spaces between or close to other aircraft. It is difficult to estimate the distance between wing tips. So during the walk-around assess wingtip distances; then, from the cockpit, look to the wing tips and learn to gauge distances from the pilot's viewpoint.
There are some tricks. On a sunny day you may see the shadows of your wing and a nearby wing on the tarmac. As long as a strip of sunlight is seen between the two shadows, the wing tips will not touch. But, not all days are sunny. Aircraft wingtip lights are also useful. By watching the reflection of light off a close-by wing tip you can judge distance. You can learn with the help of a friend and a piece of cardboard. Have your friend stand at various distances off the end of a wing, while you activate wingtip navigation lights and/or strobes. Lights project patterns on the cardboard that vary depending upon the distance. While each aircraft is different, and the wing tip of another aircraft is not a flat sheet of cardboard, there are clues. The reflected light becomes less fuzzy as the distance closes. When the reflection looks almost focused, the wing tip is as close as I want it.
This information is very helpful at night when there may be no ground crew to assist you in parking the airplane. I use this method to judge how close I can park to a hangar door. However, if you think you are too close, stop immediately, set the brakes, and shut down the engine. You can move most light aircraft by hand.
When we taxi, we want to be good neighbors. It is impolite to gun an aircraft out of a parking spot, throwing dirt and pebbles against other aircraft. We must judge where our prop wash is directed. The wind created by a prop when you begin to taxi will blast bystanders with an uncomfortable rush of air. Light aircraft can be repositioned before start so that prop wash is politely directed.
On your walk-around be sure that the nosewheel is centered. If the nosewheel is canted right or left, you will put strong side forces on the nosegear when the engine starts. If not centered, taxi will begin with a sharp turn that may not be in the desired direction and may lead to loss of control. It will take strong torque though the rudder pedals to turn the nosewheel straight, and nosewheels are not designed to sustain much of this type of abuse -- it's better to make sure that the nosewheel is centered when you secure the airplane after each flight.
Well, we are finally in the aircraft, and with engine running we release the brakes. As in all flying, think ahead. Initially more power is needed to start a taxi, but as soon the airplane is in motion the power must be reduced. If we do not anticipate this, the aircraft will rapidly accelerate to an unsafe speed. In most aircraft idle power is sufficient to keep an aircraft moving on level ground.
Therefore, once in motion very little additional power may be needed, and we probably will modulate speed using the brakes. When coming to a stop, power must be reduced to idle before applying brakes -- braking with power applied is counterproductive, and hard on the brakes. Do not taxi an aircraft faster than a brisk walk. A high-speed sharp turn puts side loads on the wheels, and tires can roll off their hubs under such stress, especially if tire pressure is low. As aircraft are three-wheeled, they are not very stable during taxi and can actually tip. Furthermore, during a too-fast taxi some lift will be developed. With less weight on wheels, turning and braking are compromised.
We are taught early in our career the correct placement of aircraft controls relative to the wind. This minimizes the chance that a wing or tail will be raised in strong winds. When taxiing into a quartering headwind, raise the upwind aileron; if it's a quartering tailwind, lower both the elevator and the upwind aileron.
Some pilots overcontrol while taxiing by pressing too much on one pedal, and then try to correct with the other lead foot. The proper technique is to taxi with heels firmly planted on the floor, and use only the balls of the feet for steering. When brakes are needed, lift one or both heels slightly off the floor and push with the toes. A technique I find useful is to taxi while maintaining mild pressure simultaneously on both rudder pedals. Steer by releasing a little pressure from one pedal, but always maintaining some pressure on both pedals. Differential pedal pressures lead to much smoother taxiing than stabbing pedals with one foot and then the other. But differential braking should be used only when absolutely necessary; apply one brake at a crawl and only when a very sharp turn is essential.
Driving a car -- in the United States, anyway -- we keep the centerline well to our left. However, an aircraft is taxied directly on the centerline. We center the aircraft on a taxiway to assure maximum wing clearances. However, novice pilots, even knowing they should straddle the centerline, may overcompensate. Because most pilots sit on the left side of the airplane, they estimate that the centerline must pass well to the right, and may taxi too far to the left. The best way to judge centering is to taxi so the centerline passes between your two knees. If you could to do this precisely, the airplane would taxi slightly to the right of the centerline. However, this would be a six- to eight-inch offset that for practical purposes is well within tolerances.
Unlike automobiles, aircraft brakes can grab, particularly when stopping from taxi speeds. As the aircraft is stopping, gradually release the brakes, so by the stop there is very light pressure on the brakes. Then, once you have stopped, reapply the brakes smoothly and firmly so the aircraft will not creep. After you gain some flying experience, taxiing seems to become a non-issue. It becomes second nature and we might assume that it no longer requires much attention. However, taxiing is not the time to unfold charts, load flight plans into the GPS, check the magnetos, or complete other in-cockpit chores. A safe taxi always includes a full stop, and then full attention can be devoted to the run-up and other preflight requirements.
A smooth and safe taxi is not difficult, but when properly accomplished it is a sign of aviation expertise.
Dr. Ian Blair Fries is a CFI, senior aviation medical examiner, and ATP, and holds a Lear 35 type rating. He serves on the AOPA Air Safety Foundation Board of Visitors and is cochairman of the AOPA Board of Medical Advisors.
Want to know more?
Links to additional resources about the topics discussed in this article are available at AOPA Flight Training Online.
Related Articles
