Taxi Smack

Copyright 2002. Aviation Safety. Belvoir Publications Inc. Access to this sample article is free. However, reprinting, republishing or reposting in whole or in part without express written permission is prohibited.

Driving the airplane to and from the runway is a piece of cake, right? Not for the dozens who prang something each year.

Many pilots appear to have the attitude that a flight begins with takeoff and ends when the airplane departs the runwayafter the landing roll. However, ground operations certainly cause their share of grief. While many taxi accidents are unavoidable, such as during bush operations, the majority fall into categories that can only be described as stupid human tricks.

A study of taxi accidents found an average of 50 accidents per year when pilots plunk slow-moving airplanes into stationary objects or get knocked over by the wind. Few of the accidents result in injuries, although the statistics include the unfortunate souls who walk into spinning propellers.

To examine taxi accidents, we ignored anything that happened from the time the airplanes began their takeoff run to when they left the runway at taxi speed at the conclusion of the landing roll. We excluded off-airport landings and losses of control on landing even if the airplane crashed on a taxiway.

Winds
Winds, both steady and gusting, accounted for 18 percent of the accidents during the three-year period we examined. Typically, the pilot is taxiing to or from the runway, or waiting in the runup area, when the airplane is stuck by a wind that sends it into the bushes, drops a wing onto the ground or causes the airplane to nose over.

Two interesting threads run through these kinds of accidents. One is that pilots tend to think of winds in terms of crosswind component rather than actual velocity. The other is that many pilots pay no heed to flight control positions while taxiing, even in high winds.

A common scenario among the wind-related accidents involves a pilot landing into strong winds that are closely aligned with the runway heading. When the pilot turns off the runway to taxi to the ramp, however, a gust blows the airplane over onto a wingtip or causes it to weathervane into the wind and head into the bushes.

Afterward, most pilots blame the problem on an unexpected wind gust, even though no substantial gusts are detected by weather stations or reported by witnesses. Other times, you wonder why the pilot was there in the first place.

Consider the pilot of a Cessna 172, who was holding for takeoff from runway 29 at Grand Junction, Colo. A rain cell was passing four miles south of the airport when the aircraft tail suddenly pitched into the air and the airplane nosed over, coming to rest inverted. Winds were measured as coming from 240 at 39 knots, gusting to 43. The pilot said she was holding the proper control inputs at the time.

The conditions during most wind-related accidents are not as severe. During the period we examined, pilots lost control with winds as low as 8-10 knots.

It may seem like these kinds of accidents are monopolized by taildraggers – and many of them do involve tailwheel airplanes – but nosewheel airplanes accounted for more than half. Interestingly, 25 of the 27 accidents in this category involved high-wing airplanes. The others involved a Stearman biplane and a Cessna 310.

Ground Obstructions
Tied with winds at 18 percent of the 149 accidents we analyzed were collisions with ground obstructions, notably buildings, poles, fences, trucks and parked airplanes. We eliminated the accidents that occurred as the pilot was maneuvering after making an off-airport landing, such as to a road.

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The biggest hazard here was night operations on dark ramps where the airplane struck an unseen object. Given the short life of the taxi/landing lights installed in light singles and the poor lighting on most GA ramps, this is perhaps understandable. But many of the accidents happened in broad daylight when the pilot either misjudged the wingtip clearance or was focusing on an obstruction on one side of the airplane and struck something with the other wingtip.

Hitting buildings and vehicles were about evenly distributed, with hangars and fuel trucks taking the brunt of the abuse. Poles, taxiway signs, fences and trees were also well represented.

Frustrating to many owners is the fact that parked airplanes also take their share of abuse as taxiing pilots either lose control or inadvertently smack into a prop or wingtip of an airplane that's unoccupied. For the innocent airplane, that often results in a damage history that devalues the airplane despite a competent repair.

Pilots frequently blamed the lack of depth perception on faded or missing taxiway striping, unfamiliarity with the airport or poor lighting.

However, investigators frequently found those claims hollow, blaming most of the accidents on impatient pilots wanting to squeeze through an area of uncertain width instead of waiting for the fuel truck to move, for example. Another common error was for pilots to taxi off the pavement and run into a sign or other obstruction in the grass, or head down an embankment. Progressive taxi instructions from the ground controller or a little study of the airport layout in advance would make most of these accidents history.

Colliding airplanes
The next most common kinds of taxi accidents, with nearly 15 percent of the total, were collisions between two airplanes. Many involved tailwheel airplanes in which the pilot did not have enough room to make the required S-turns or where the pilot was looking out one side when the other side struck another airplane. Some involved airplanes taxiing in opposite directions trying to get by on a single taxiway.

A typical scenario involves an airplane that has cleared the runway, waiting for permission from the controller to proceed across another taxiway or runway. Meanwhile, another airplane lands and exits the runway at the same spot. Another common situation is an airplane approaching a crowded runup area and either striking a waiting airplane while trying to taxi past it or not stopping in time and striking the empennage of the waiting airplane with a prop or wingtip.

Some pilots contend the accidents happen despite their best efforts. A Stearman and a Cessna 182 got tangled when the Stearman was on its takeoff run and the Cessna encroached on the runway from a taxiway. The grass field required pilots to back taxi from the taxiway/runway intersection to the approach end of the runway.

The Stearman was in position on the runway and holding, waiting for a landing airplane to clear the runway. As it held, the Cessna approached the runway on the taxiway, broadcast its intentions to back taxi, and then stopped. The Stearman was not equipped with a radio and, as the tail of the biplane lifted, the right wing hit the Cessna's nose.

An analysis of a videotape of the crash showed the Stearman tracked parallel to the runway centerline, though slightly right of the centerline, and the Cessna's nose and right wing had encroached over the runway.

Other accidents involved pilots following the instructions of a ground controller, only to discover when metal crunched that the controller had made a mistake. Those are the kinds of accidents that can't happen if pilots keep their eyes outside the airplane.

Mechanical problems
Trouble with aircraft systems, particularly landing gear, contributed to about 11 percent of taxi accidents. While it may be tempting to throw up your hands and say there's nothing you can do if a part suddenly fails, the record shows that's seldom the case.

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Brakes catch on fire when pilots ride them or try to taxi with the parking brake engaged. Landing gear fail after a hard landing or nosewheel-first touchdown. Sometimes the airplane's tires are simply underinflated or overinflated.

The solution for these problems is obvious: better preflight inspections. Most pilots make only a cursory check of the wheels. Few examine the brake cylinders or pads. Even fewer get out a tire pressure gauge.

Even without that level of diligence, there are clues that the landing gear isn't right. A quick pump of the brakes when you leave your parking space will alert you to a spongy brake due to air in the line. If the pedals are firm but the airplane pulls to one side, you'll know you're destined for trouble on landing.

During taxi, a bouncy ride or one in which the airplane pulls uncommanded to one side indicates tire pressure or landing gear alignment needs to be looked at. A nosewheel shimmy may indicate trouble ahead due to a nose-first touchdown.

But sometimes a mechanical problem can be more bizarre. A flight instructor and multi student were taxiing a Baron to parking when the student began a turn the instructor deemed too tight. The instructor countered with left rudder, and the two battled for nosewheel control until the rudder pedal bell crank broke.

At that point, they shut down the airplane and pushed it by hand to parking.

While no airplane can undergo a comprehensive mechanical inspection prior to every flight, pilots should be sure to check brake operation, tire inflation and general landing gear condition. Proper landing technique – and a careful check after the occasional hard landing – will also go a long way toward keeping the airplane out of the weeds during taxi.

Racy Behavior
Most airplanes are made to go as fast as possible, but their ungainly ground manners mean the taxiway is not the place to employ that speed. Taxiing too fast was responsible for about 9 percent of the accidents studied.

These accidents happen in several ways. Making a turn at too high a speed can tip the airplane and drag a wingtip. You may be unable to stop and head off the pavement and into whatever mysteries await you there.

A typical accident involved a Cessna 411. After landing the pilot attempted to make a 130-degree turn onto a taxiway. The left main gear collapsed and the left wing spar was damaged.

A not-so-typical accident involved the pilot of a rented Mooney who had a habit of turning off the master switch to save on rental charges, which were based on an electric-powered Hobbs meter. As he taxied in on an unlit taxiway at a high rate of speed, he lost sight of the centerline, went off the taxiway and down an embankment.

Or how about the pilot who was flying a Taylorcraft from the right seat to get accustomed to that side so he could give flight instruction. After a solo flight, he made a high-speed taxi and apparently then realized the airplane was not equipped with brakes on the right side.

After a flight leg at 150 knots, that "walking speed" taxi to the ramp two miles away can certainly try anyone's patience – especially if faced with a spouse who's eager to find a restroom or an associate who's late for a meeting. But keep in mind that airplanes are optimized for traveling in the air, and their ground manners are even worse than that Volkswagen Bug you drove in college.

Hands Down, Please
In this age of advanced avionics, the fact that you can hand-prop many light airplanes seems quaint. Yet when faced with a dead battery, some pilots are willing to give it a try – even if they're guessing at the correct procedure.

We found seven instances in three years of pilots who hand-propped their airplanes, which then proceeded across the ramp without them. In this sample, most of the accidents involved people with no experience hand-propping airplanes trying to start engines that were equipped with electric starters, including a Bonanza, Cessna 172 and Ercoupe.

There were two other accidents we included in this category just because they fit the same general mold – people who got out of airplanes while the engine was running, leaving the airplane to do whatever it wanted.

In one case, the pilot had forgotten to remove the wheel chocks and got out to take care of that task. In the other, the airplane wouldn't taxi and the pilot wanted to check if the chocks were there. In both cases, it seems like the thoughtless pilot got what he deserved.

When the engine is running – or when you hope the engine is about to be running – make sure a competent person is on board holding the brakes or that the airplane is tied or chocked securely. And if you're going to hand-prop an airplane, get someone with experience to show you the right way.

Pay Attention
Finally, there's a catch-all category we'll call inattentive occupants. These are the people who get out of the airplane and walk into a spinning prop. They're the pilots who start the engine and bury their heads in the cockpit to work radios or fold charts while the airplane meanders across the ramp.

They taxi down perimeter roads and hit poles. They start taxiing with one wing still tied down, spinning the airplane in a circle and crunching something nearby.

One pilot who was taxiing in thought it critical he retrieve a chart that had fallen on the floor in front of the right seat. He rammed a trailer that had been parked on the taxiway.

The variety of miscellaneous accidents also illustrates how problems can sneak up on you. The airplane can get blown over by a jet blast or prop wash from another airplane. You can stumble into a construction zone. One pilot's sleeve caught on the throttle and advanced it to full power suddenly.

Taxiing is usually the least demanding part of a flight, a fact that leads many pilots to discount the need for attention or to attempt to multitask on their way to the runway. The rolling runup used by some charter operators comes to mind.

Taxi accidents prove the wisdom in an old saying usually applied to tailwheel airplanes: Fly it from the time the engine starts until you shut the engine down.

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Also With This Article
"Taxi Accidents (1997-1999)"
"Tricks and Traps"

-by Ken Ibold

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