Ten Extra Knots and 100 Extra Feet — Always a good thing?

by William S. Lawrence, USMC (retired) on May 3, 2011

in Aviation Safety

On the famous list of “Things That Do You No Good in Aviation” are the following: the airspace above you, and the airspeed you don’t have. There are more of course, but I want to focus on these because, in the past two decades of looking at controlled crashes following engine failures, I have come to appreciate a couple of things.

All of us who fly have grown up believing that extra airspeed is a good thing and a few extra feet just can’t hurt. And, in general, that’s pretty much true. But when your engine fails and you’ve found the perfect farmer’s field to belly in, you need to be “on” airspeed and “on” altitude, neither low and slow nor high and hot. The question arises: what is “on” airspeed and “on” altitude?

In the first place, there may be a substantial delta between what you think your descent rate is going to be when the engine quits and what it actually is. if you haven’t experienced a dead engine glide in your airplane with the prop stopped, you definitely have a surprise in store. A simulated-dead-engine airplane with an unfeathered windmilling propeller has a lot of drag that will increase the descent rate by a substantial amount. I’m not going to suggest that you go out, shut your engine down, and stop the prop to experience the true descent rate you would get with an engine failure. You might just end up needing to execute that no-kidding dead stick landing. But in my trusty Bonanza the checkout instructor suggested that experiencing a self-induced engine failure might be a very good thing. And I believe he was right. But perhaps a word of caution, should you decide this might be a valuable experience. Shut your engine down several thousand feet above an airport with multiple runways and wait until you’re the only guy above said airport. Oh, and know your engine restart procedures cold — both for a windmilling prop and for a stopped prop.

The second thing is that I believe we have a built-in urge to hold airspeed and altitude. “What if I misjudged and I’m too low to make the field, and don’t have extra airspeed to stretch the approach? I’ll crash short.” Nobody ever seems to consider the possibility of sailing over the proposed landing spot into the trees on the other side of the field. You might be surprised at the number of “engine failure” controlled crashes that end up overflying the point of intended touchdown.

The third thing is that I just bet most general aviation pilots have no idea how much descent rate is changed as a function of flap and gear extension. If you need to get down in a hurry, it would be helpful to know how to increase your descent rate by increasing your drag. Conversely, if you are coming down too quick, perhaps it’s because you didn’t raise your gear and/or flaps.

Maybe the fourth thing is that we’ve been so over-convinced that balanced flight is the only way to go, we forget that flying in a slip is a way to come down fast. Wouldn’t it be a shame to overshoot the perfect field because you just didn’t think to kick the ball out and come down faster in a slip?

My point, as always, is to be prepared. Give thought beforehand as to how you would deal with an engine failure. Know the procedures for engine restart cold. Practice them in your airplane before you start it up. Understand the logic behind the procedures because we remember best what we understand best. When you are flying, look at the ground and pick out places you would choose to land if your engine quit. Fly controlled approaches at different airspeeds, power settings, and configurations to better understand their effect on descent rates. Practice sideslips to understand how out-of-balance flight affects descent rate. I’ve investigated crashes where the pilot overflew the perfect field, crashing on the other side with his landing gear and flaps up.

With my helicopter pilot hat on, I used to say, “Not a good thing to experience your first full autorotation only when you experience your first engine failure”. The same is true with my fixed wing pilot hat on. I don’t want my first dead stick landing to be as the result of an engine failure. In an extremis situation, there is enough going on and your mind is full enough without having to deal with unknowns that didn’t have to be.

{ 1 comment… read it below or add one }

James T. Crouse May 3, 2011 at 12:33 pm

Another insightful post from Colonel Bill Lawrence, this time talking about the avoidance of preconceptions and he need to be prepared in aviation. How many of us need to hear that advice? Even as airline passenger, do you choose where to sit because of its proximity to an exit? Have you ever visualized the mayhem in an airliner cabin that would occur after a crash, and thought, “If ‘A’ happens I will do ‘X,’ if ‘B’ happens I will ‘Y,’ etc?.
But his advice pertains not only to aircraft, but also in driving our cars, household and workplace safety. When we get in our cars, do we think about the things that could happen? When is the last time you checked your tire pressure, or did a thorough visual inspection of belts, hoses, tires and the underside of your car? In the last thirty days, have you actually checked around your workplace for items that can create a hazard for you or someone at work? I mean a walk around just for that purpose?
What about at home? Have you thoroughly looked in your children’s rooms and play areas? What is in the garage or under that could prove hazardous—if not deadly? If you have guns and knives, are they secured—really secured?
The recent tornadoes should be a call to us all to PREPARE! Where would you and your family go—including pets? Do you have fire ladders for all of your second floor rooms? When the tornado is bearing down or when the fire is raging, it’s too late.
And if you must drive on slick roads—when’s the last time you actually practiced skid recovery? Check with your local law enforcement—they can help.


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