Taxiing procedures

Definition: Steps to assist in the process of self-propelled aircraft movement on land.
Significance: Taxiing procedures are essential in moving aircraft to and from runways. Despite its apparent ease, taxiing demands pilot vigilance, as many mishaps occur during taxi.

History and Techniques

Before airplanes may take off for flight, they must travel from the parking ramp to the runway. Although most accomplish this by taxiing, that was not always so. The first flying machines, such as Otto Lilienthal's foot-launched gliders, Samuel Langley's houseboat-launched Aerodrome, and Wilbur and Orville Wrights' rail-launched Flyer, were not designed with taxiing in mind.
Soon, however, aircraft designers abandoned landing skids and foot-launches for humanity's oldest convenience, wheels. Even so, early wheeled airplanes could not taxi. Aircraft such as Louis Bleriot's famous monoplane required handlers to trundle the airplane into the takeoff position or roll it to its parking spot after landing. Bleriot and other early designers included main wheels to trundle their flying machines into takeoff position, and to the parking area after landing, but placed skids at the tail to retard movement on landing. Taxiing moves an airplane under its own power, using the airplane's control systems to steer.
By 1918, airplanes had grown large, and engines had attained enough power to make the labor-intensive trundling method inefficient. Eventually, the tail skid was replaced with wheels all around, one of which was steerable. It was extremely difficult to use the trundle method of ground movement to move the huge bombers built by manufacturers in Germany and England. Certainly, after World War I, taxi techniques had become well established.
A 1930's development was the tricycle landing gear. Tricycle landing gear places the third wheel under the nose, bearing the weight of the engine while the aircraft is parked or taxiing. That extra weight provided traction during taxi and reduced nose-over accidents when pilots applied brakes too enthusiastically. Tricycle landing gear lowered the nose permanently for taxiing, so pilots could look over engine cowlings to enjoy approximately the same view automobile drivers would see over their hoods. By the 1950's, the term "conventional landing gear" denoted the tail wheel type, because the word "tricycle" had become standard for the increasingly popular nose wheel system. By the end of the twentieth century, few manufacturers built tail wheel airplanes, although the tail wheel remained popular with amateur builders.
Designers learned quickly that flying machines, though at rest on the ground, remain subject to the wind. Because winds can be unpredictable, pilots taxi airplanes slowly, so that moving the throttle to idle allows a prompt stop. When taxiing into the wind, wings produce lift, which reduces brake and steering effectiveness. Because strong winds have overturned taxiing airplanes, pilot training since the 1940's has included positioning the flight controls so as to keep the wind flowing over the top of the airplane structure. For new pilots, automotive driving habits slow their learning to taxi. Taxiing pilots steer by using foot controls, or rudder pedals, andmostbrakes are activatedby pressing the top of these pedals. This takes some acclimation.
Landing gear design also affects pilot taxi technique. Tricycle airplanes are easy to taxi. Tail wheel airplanes require greater attention. Wide landing gear makes taxiing more easy than does narrow gear. The wide-landing-gear design saw an extreme expression in the 1980's, when one amateur-built airplane appeared with wheels at each wingtip. The popular airplane was stable but could not negotiate very narrow taxiways.
Taxiing surfaces also affect taxiing procedures. Not all taxiing surfaces are clean and strong. They range from well-maintained concrete at major airports to narrow dirt strips at ranches and even to riverbanks and sandbars. Taxiing techniques must accommodate each of these. Generally, tail wheel-type airplanes are more suitable to rugged taxiing surfaces than are nose wheel-type aircraft.
Modern pilots learn to control their airplanes from first movement. Taxiing demands alertness, and pilots must keep track of the movement of everything else along the taxi path. Right-of-way issues and individual pilot habits make taxiing on busy airports an effort in safety. To observe the entire area, pilots must look around in a complete circle, which few airplane structures allow. Airport space is extremely valuable, so parking areas place airplanes closely together. Pilots must avoid people, other aircraft,and obstructions when taxiing. During the 1990's, pilot training in the United States began to require that pilots verbally announce "clear right" or "clear left" when taxiing past taxiways, runways, and parked aircraft or other obstructions.

Water Taxiing

Seaplanes also taxi, and taxiing on water demands nautical, as well as aviation, skills. Water operations allow pilots to taxi with about two-thirds power, in a technique called step taxiing. Seaplane pilots use a step taxi when the takeoff or landing area is distant from where the seaplane will moor, or anchor. When not step taxiing, seaplane pilots taxi slowly when they are near the shore or at any time when speed would be hazardous. Because water is fluid, seaplane pilots must give even more attention than land-plane pilots to the wind while taxiing.

Taxiing Accidents

Accidents do occur during taxiing. The two most common reasons for taxi accidents are pilot distraction or inattention and taxiing too fast for conditions. It is difficult to set rules for safe taxiing speed, because circumstances and conditions continually change. What is prudent one day
may be rash or reckless the next. Traditionally, pilots have used the phrase "a brisk walk" to describe a prudent speed. However, if a pilot needs to stop immediately, even that speed may be too fast. A third cause for taxi accidents or incidents is a pilot's holding the flight controls improperly for the wind conditions. Taxi accidents tend not to be newsworthy events, but are dangerous nonetheless. In all, taxiing, like flying, can be safe and enjoyable when responsible pilots follow procedures.