Page 40 - March 2015 Volume 19 Number 3

Why Pilots
by LeRoy Cook
Arunway excursion accident, particularly one that occurs at very near flying speed, is an extremely hazardous affair. High performance airplanes are normally designed for level, prepared and evenly-paved surfaces. They do not comport themselves well when caused to operate on footings other than runways, and the accompanying structural failures often result in fires, injuries and deaths. So, why do pilots of otherwise perfectly-functioning aircraft run off runways?
One prime ingredient of these off-runway excursions is lack of consideration for the surface wind. We have all seen the videos of airliners wallowing back and forth across the runway centerline in extreme wind conditions. However, such situations are rare, and pilots will usually rise to the occasion with consummate skill. It’s often the less-aggressive wind that catches pilots unprepared, because it was disregarded as a factor.
However, even a mild tailwind skews the landing and takeoff- distance charts by a major increment, and a substantial tailwind component, such as 10-15 knots, creates a huge difference. From the King Air F90 takeoff charts, for instance, a 10-knot headwind would reduce ground roll by about 150 feet, while a 10-knot tailwind increases the ground roll by 350 feet. Even more disparity becomes evident when figuring the distance to climb over an obstacle. Landing distances are similarly affected.
There are other implications to operating in a tailwind. A slick runway, combined with a following wind, brings the potential for hydroplaning at a much slower airspeed than normally expected.
• • • •TWIN & TURBINE
Run Off
Rudder control becomes zero as a tailwind matches aircraft speed, leaving only braking as a means of steering unless the nosegear is solidly planted.
Forcing The Issue
In January, 2014, a Challenger 601 crashed during an attempted landing at Aspen, Colorado. While not technically a runway excursion, since the accident took place on the runway, it certainly involved loss of control with a 25-knot tailwind’s influence. Touchdown occurred some 3,500 feet beyond the landing threshold, a forced arrival that resulted in a bounce, followed by a fiery inverted crash. It was the crew’s second attempt, after a 33-knot tailwind had prompted a go-around on the first try.
Which brings us to a significant ingredient of runway excursion accidents while attempting to land; it’s termed “landing expectancy”. When the pilot is fixated on the goal of touching down, there’s a tendency to ignore signals that an alternative course of action should be taken. We want to get the aircraft on the ground; we do not want to give up short of the objective. Because we expect to land, we make that the only acceptable outcome. The passengers, after all, want to arrive on time, at the intended destination.
Leaving The Runway Before Liftoff
A takeoff, pursued beyond the point of practicality, is also subject to expectancy. While performance calculations predicate a continued roll to liftoff and climbout once V1 speed is attained, that doesn’t mean one should totally ignore signs of sluggish acceleration, or loss of directional control early-on due to adverse winds. Along with devotion to the balanced-field concept,
there must be interpretation of the aircraft’s control and speed. Abandoning a takeoff is not to be taken lightly, but if done early, it’s a sensible course of action. Takeoffs, after all, become more and more hazardous as kinetic energy builds during the maneuver, while the opposite is true of a landing rollout.
The late-May 2014 crash of a 2000-model Gulfstream IV at Bedford, Massachusetts bears tragic witness to the kinetic energy of an airplane running off the runway at takeoff speed. In the 50 seconds leading up to the crash, the G-IV had attained 165 knots, with preliminary indications showing that braking and thrust reverse had been initiated. It was too late, however. The aircraft impacted a localizer antenna and fence after running past the runway end, coming to rest 1,850 feet from the runway; everyone perished in the ensuing fire. Sadly, there’s some FDR evidence that the controls gustlock may have remained engaged.
Other Factors
Distractions like obstructions or an unfamiliar airport layout can cause pilots to forget about the precise job of control they must do if they are to stay on the runway, let alone maintain the centerline. A visual approach over obstructions leads pilots to “pad” their threshold- crossing height, which results in a touchdown taking place farther than normal downfield. Another
MARCH 2015