Ground Control

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Maintaining control of an airplane while it’s on its wheels becomes a lot easier once you understand it’s a really lousy ground vehicle.

I basically live at an airport, and taxi to and from the airpark’s runway over what are residential streets the rest of the time. My normal taxi route includes a stand of bamboo, decades-old oak trees, mailboxes, a power pole and assorted fences. Tuesday is trash-collection day, and it can be a deal if your airplane has a low wing. Like mine.

My flight instructor also lives in an airpark development, about 40 nm away, an easy hop. When we fly together, I generally taxi directly to her home. Past palm and pine trees, mailboxes, fences and... well, you get the idea. (Her trash gets collected on Fridays.) So I’m no stranger to ground operations in close quarters. It could be said that I don’t really know what to do with all the expansive, unobstructed pavement available for taxiing at “real” airports. That’s not to say I’ll never taxi into something; that’s always a risk.

But ground operations are a lot more than just navigating the chicanes on trash day. They start at the hangar or tiedown when we release the brakes and don’t end until liftoff. At the other end, they begin when the third wheel touches the runway and—you guessed it— continue until the engines are shut down. Brakes and steering justifiably get the lion’s share of attention when it comes to ground operations, but all of the flight controls—and especially the power controls—can figure prominently in how safe and sure we are on the ground.

The Basics

According to the NTSB, the solo ATP flying this Cirrus SR22 landed “while travelling about 100 knots” then “taxied about 3.7 miles with the engine operating between 1200 and 1600 rpm.” Considering that the Cirrus has a castering nosewheel and brakes are the primary directional control when taxiing, the brake system fire that consumed its aft fuselage was inevitable.

It shouldn’t have to be said that driving a car has little to do with controlling an airplane on the ground. The only real similarity is that both involve a wheeled machine typically powered by an internal combustion engine. For the most part, the special concepts and skills of one activity really don’t transfer to the other. But that doesn’t stop some pilots from trying to drive their airplane on the ground. In fact, after years observing both my own taxi operations and those of others, I’ve settled on misusing the power controls and the brakes as the primary ways pilots screw up ground operations. Countless times, I’ve watched as a piston airplane came to a stop on a ramp with its engine turning at well above idle speed. I’ve also often caught myself using too much power, especially in confined areas.

Using too much power—and often taxiing too fast as a result—goes hand in hand with overuse of the airplane’s brakes. The flivvers I fly have steerable nose- and tailwheels, so I don’t have to depend on the brakes to maintain directional control on the ground unless I’m flying a different airplane. When I do fly a Cirrus or other type with a castering nosewheel, I’ve found that one trick to taxiing it is to use a low enough power setting, and resulting slow taxi speed, that only occasional use of a brake is needed to straddle the centerline.

If you think you’re taxiing too fast, you probably are. A good way to determine how fast you’re taxiing is to simply use the GPS. I’ve found that taxiing at a groundspeed of 20 knots is about as fast as I need to be going, and that only when on a wide-open taxiway with no other airplanes nearby. Around my residential airpark, 10 knots is my speed limit, which gets reduced to five or less—just a bit faster than walking speed—when I’m in a congested area or on a busy, crowded ramp.

Put another way, if you’re constantly juggling power, directional control and brakes while taxiing, there’s either something amiss with your airplane or you’re doing it all wrong. On a taxiway, pick a (relatively calm and sedate) power setting and allow the airplane to accelerate or decelerate to match it. If conditions—wind, visibility, traffic, obstructions—conspire to call into question your control of the airplane at that power setting, don’t depend on the brakes alone to get you out of trouble. Reduce power, then use the brakes to slow down, and only add back enough thrust to keep moving at your new taxi speed. This isn’t rocket science, and your chances of remaining under control, even in lessthan-perfect conditions, remain high.

Flight Controls

Another pet peeve I see a lot is when pilots apply the brakes at the end of a long taxi or short-field landing: The nose dips as the tricycle-geared airplane decelerates while the pitch control is ignored. That places more of the airplane’s weight on the nosewheel, which can lead to abnormal strut and tire wear. In extreme cases, it can lead to losing control or a prop strike. Some of this is going to happen anyway, but it can be minimized, especially if we plan ahead and reduce power well before we might consider slowing down in a car. The problem is especially acute when using a parallel taxiway on our way to the departure runway—almost by definition, we’ll have a tailwind for this portion of our taxi operation, which just places more demand on the brakes.

The first solution is a simple one: Apply full nose-up input to the pitch control throughout the braking maneuver. This puts as much of the airplane’s weight as possible on the main wheels—the ones doing the braking—and minimizes forces on the nosewheel or dipping the nose. That latter point is more important on unpaved surfaces like gravel or even turf, but you really don’t want all that weight on the nosewheel, regardless.

The other solution is to plan ahead: You see the end of the runway looming hundreds of feet in front of you. Now’s a good time to reduce power and let the airplane begin to decelerate. Once you feel you need to use the brakes, apply them steadily instead of using a pumping action. Pumping the brakes offers yet another opportunity for losing control since one side usually is a bit stronger than the other. When applied strongly and quickly, the airplane may want to dart toward the strong brake. Releasing the pressure you’ve applied means you’re not getting all the braking you’re seeking. That’s fine if you have plenty of clear area between you and the run-up pad, but it’s not fine if you’re running out of space and/or there are obstacles (e.g., other airplanes) in the way.

Establishing a nose-up attitude to maximize braking is only one of the ways we can use the primary flight controls on the ground. Thanks to our training, we all should be familiar with the graphic below demonstrating how to position the flight controls in windy conditions. The idea is to help minimize an airplane’s tendency to, well, fly in strong winds and help prevent them from lifting a wing and forcing us to lose control, or even tipping an airplane so far off its wheels that ground contact and damage occur.

I’ve never really liked that diagram because there’s too much for an inexperienced pilot to absorb and the descriptions are subject to interpretation. The key to it is this: Deflect the primary flight controls— rudder, elevators and especially the ailerons—so they apply downforce on the airframe, not lift, in windy conditions. For example, if the wind is from the tail—as it usually is when taxiing to the runway end before turning 180 degrees into the wind and taking off—position the airplane’s pitch control so that any wind striking the elevator/ stabilator pushes the tail down, not up. In other words, move the pitch control to the full-forward, nose-down position. Neutralize the pitch control when taxiing into a headwind. That way, the tail won’t exert enough force to lift the nosewheel off the ground when there’s a lot of wind—or the 737 in front of you sets breakaway thrust to taxi into position (see the sidebar below). The diagram offers more details on how to position the flight controls when taxiing in stiff winds. While high-wing airplanes and taildraggers are most susceptible, proper control position is necessary in stiff winds no matter what you fly.

The real challenge when taxiing in stiff winds is positioning the ailerons, because the wings they’re attached to will generate lift in windy conditions, no matter how slowly we taxi. We need to place them in a position optimized to keep the wing from lifting. Keeping the wing from lifting—“flying,” if you will—also will keep the wheels on the ground and enhance braking action.

The diagram above encourages us to position the ailerons so as to minimize any lifting of the wings a quartering head- or tailwind may create. We do that by either spoiling the lift (i.e., raising the aileron on the upwind wing) if the wind is coming from a front quarter of the airplane or lowering that aileron (again, the one that’s upwind) if the wind is from a rear quarter. Lowering the aileron into a quartering tailwind will cause the wind to tend to push down on that wing, instead of lifting it. When the wind is square on the nose or tail, move the ailerons to the neutral or level-flight position.

Rather than try to memorize this diagram, just remember that you want to counter the wind’s tendency to lift the airplane, and you do that with the elevator/stabilator and the ailerons.

On And Off The Runway

Few wind conditions, however, impose greater demand for correct control positioning on the ground than the takeoff and landing portions of our flight. Even though the wheels might be on the ground, we’re still moving at a relatively good clip when rolling out after touchdown or while accelerating for liftoff. Anyone who’s gotten good at handling crosswind takeoffs and landings knows that positioning the controls to help counter the wind is part of the overall technique.

If you haven’t gotten good at crosswinds, maybe it’s because you don’t understand how the primary flight controls can work in your favor when the wheels are still on the ground. The fact is you still have to “fly” the airplane, and you do this by using rudder, pitch and roll to keep it pointed where you want it to go. No exceptions.

The taxiing diagram above may help you understand how to deal with crosswinds when taking off or landing. Without turning this article into a treatise on crosswinds, the simple (in conception, perhaps not in execution) idea is to keep the upwind wing from being lifted by the wind. Doing so helps keep the associated main wheel on the ground with some force, helping ensure it doesn’t get light and skid under braking or lose traction altogether on slick surfaces.

Basically, we’ll end up putting in all the aileron available into the wind as we roll out and slow down while using the rudder, small-wheel steering if available and differential braking to maintain directional control. On takeoff, the inputs will be reversed: We’ll want to start out with all the aileron available and slowly take it out as we accelerate, leaving in just enough to keep the upwind wing slightly low—sometimes with opposite rudder—to help counter the airplane’s weathervaning tendencies.

A lot of pilots screw this up when taxiing onto the runway for takeoff or when clearing it after landing. We’ll get so focused on the crosswind runway operation that we forget we still have to taxi to and from it. For example, presume a stiff crosswind from the runway heading’s left, translating into a quartering tailwind as we sit on the upwind side of the perpendicular taxiway. Cleared onto the runway, start out with some aileron opposite the crosswind (i.e., the upwind aileron positioned down). As we turn 90 or so degrees to line up on the centerline, that quartering tailwind becomes a quartering headwind. To properly compensate for it, we need to take out all of the opposite aileron we rolled in on the taxiway and then add some input—perhaps all of it—to raise the upwind aileron into the crosswind.

Ground operations aren’t the most fun we can have in an airplane, but they’re necessary to get to and from the runway. Since we’re a whole lot closer to obstructions and other aircraft, we can’t treat the airplane like the car we drove to the airport. It doesn’t have the brakes or the handling. Instead, treat it for what it is: a really lousy ground vehicle.

Minimizing Incursions

The FAA says an average of some three runway incursion events—which the agency defines as “any occurrence at an aerodrome involving the incorrect presence of an aircraft, vehicle, or person on the protected area of a surface designated for the landing and takeoff of aircraft”—occur each day at towered airports in the U.S. The three main ways pilots are responsible for runway incursions are crossing a runway hold marking without clearance from ATC, taking off without a clearance and landing without clearance.

According to the FAA, “approximately 65 percent of all runway incursions are caused by pilots. Additionally, 75 percent of the 65 percent of runway incursions are caused by GA pilots.” Investigations of runway incursions over the years conducted by the agency have identified three major areas contributing to these events:

  • Failure to comply with ATC instructions/clearances
  • Lack of airport familiarity
  • Non-conformance with standard procedures.

Tools like writing down your taxi clearance, monitoring your progress with an EFB app and requesting progressive instructions at unfamiliar airports can help minimize runway incursions. Situational awareness is the main ingredient that will keep us where we’re supposed to be.

Keeping Your Distance

At a large Class C airport recently in my Debonair, I was cleared to taxi to the departure runway behind a Southwest Boeing 737. Aware of the wind that a pair of jet engines can generate, I remained at least a couple hundred yards behind the 737 and followed my taxi clearance.

Although there was no one behind me, the controller saw fit to urge me to taxi faster and close the distance. I don’t recall my exact response, but it settled the question and we all went on about our business.

According to NASA’s Aviation Safety Reporting System, jet blast more than 200 feet behind large jets can generate wind forces approaching 100 knots, a speed at which many airplanes are quite happy to fly.

Jeb Burnside is the editor-in-chief of Aviation Safety magazine. He’s an airline transport pilot who owns a Beechcraft Debonair, plus half of an Aeronca 7CCM Champ.

This article originally appeared in the August 2018 issue of Aviation Safety magazine.

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