Missed Approach
(continued) The 560 crew faced much the same situation and the captain delayed the initiation of a go-around until the first officer asked if they were going around. The aircraft lifted off before departing the paved overrun. It hit a localizer antenna platform 304 feet off the end of the runway and 2 feet lower than the elevation of the end of the runway. It went 400 feet farther, over downsloping terrain before colliding with terrain and a commercial storage building that was approximately 80 feet lower than the end of the runway. The four people in that one perished.
The moral to the story is clear. If you press on into a landing out of a lousy approach, a point is passed where a successful go-around is impossible. There is no way to know precisely where that point is but the record suggests that once the wheels of the airplane are on the ground, they are best left there. Certainly an accident that occurs when you are slowing down can have a better outcome than one where you are speeding up.
There is another critical point on an approach where a last-minute grade on the approach needs to be made. On a precision approach, where the glideslope will take you to a touchdown point about 1,000 feet down the runway, the threshold crossing height (TCH) is usually 50 feet. Why is that critical? Well, it's where an important characteristic of the airplane starts to change. Once the airplane is in ground effect, which is in full effect at an altitude half the span of the airplane, the airplane decelerates more slowly, about half as rapidly, than it decelerates out of ground effect. This characteristic is especially marked on airplanes that sit low to the ground, as do the 500 series Citations and Mooneys to name a couple.
So, if the speed at the TCH is a little high, best get rid of the extra knots before the airplane settles into ground effect. If the speed is a lot higher, then the approach should be missed unless the runway is many times longer than the value shown in the book for the airplane.
The effect of extra speed on landing distance can be pronounced, especially if that extra speed is maintained into ground effect and the landing flare. You can take available numbers and calculate a 10 percent increase in the landing roll for each 2.5 knots speed over the POH touchdown speed. You can also postulate a 20 percent increase in landing distance for each 2.5 knots over Vref at 50 feet on approach if the extra speed is carried into ground effect. Most of our book landing distance numbers are low but can become long when you start adding substantial percentages for knots of extra speed.
Another reason to miss an approach that is flown too fast is that it makes the landing that follows awkward at best and damaging at worst. Tricycle-gear airplanes are designed to be landed on the main wheels first. If the nosewheel hits first, either because the pilot "plants" the airplane on the runway at high speed or bounces and enters a pilot-induced porpoise, then the nose of the airplane is in great jeopardy. Bent firewalls, collapsed nosewheels and damaged propellers are common occurrences. Life is much better if a go-around is initiated early on, or at the latest, at the threshold crossing height if everything is not just right.
In tailwheel airplanes it's possible to land at higher speeds safely by making wheel landings or by flying the airplane onto the runway on the main wheels first. There the technique is actually to add a little forward pressure on the stick or wheel at the moment of touchdown. That does not work in tricycles.
In a tricycle-gear airplane the only way to safely touch at a higher speed is to use less than full flaps. So if a crosswind or turbulence dictates a little extra speed, consider landing with less than full flaps. Make sure there is adequate runway, remembering that, for example, 10 degrees less flaps might mean a 5 knot higher touchdown speed. That in turn might increase the landing roll by 20 percent. If this doesn't calculate, miss the approach and go to a longer runway more nearly aligned with the wind.
Discuss this article in our forums
| 
Copyright @ 2009 Bonnier Corp. All Rights Reserved. Reproduction in whole or in part without permission is prohibited.
