Plane & Pilot
Wednesday, March 1, 2006

Spins


The realities and the rumors


SpinsThe “Shall we or shall we not teach spins?” debate has been raging since spins were removed from the private-pilot curriculum decades ago by the FAA, who preferred instead to concentrate on stall recognition and prevention. Under today’s FARs, only flight instructor candidates are required to do spins. Even then, it’s usually not in-depth training because all the candidate needs is a logbook entry saying that he or she has seen spins. We won’t get into that debate except to say that as an industry, we must be doing something wrong because stall/spin accidents are still killing people.

 

 

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Spins
A spin is preceded by a stall. While the topic is still hotly debated, current FAA standards emphasize teaching student pilots how to avoid an approaching stall, as opposed to learning how to recover from the resultant spin.

The “Shall we or shall we not teach spins?” debate has been raging since spins were removed from the private-pilot curriculum decades ago by the FAA, who preferred instead to concentrate on stall recognition and prevention. Under today’s FARs, only flight instructor candidates are required to do spins. Even then, it’s usually not in-depth training because all the candidate needs is a logbook entry saying that he or she has seen spins. We won’t get into that debate except to say that as an industry, we must be doing something wrong because stall/spin accidents are still killing people.

It would be more productive to dissect the anatomy of a stall/spin accident and then come up with preventative measures because, in our eyes, the problem isn’t that people don’t know how to recover from a spin. The problem is that they don’t know what they’re doing wrong to cause the spin in the first place. The underlying failure isn’t in not teaching spins, it’s in not teaching the basics of flying clearly enough to prevent spins.

First, a couple of iron-clad truths. For an airplane to truly spin (not spiral), it absolutely must be stalled and it must have excess yaw (the ball is way off center). If one of those factors is missing, then the airplane won’t spin. If it has excess yaw but has flying speed, the nose will slide off to the side and will probably drop, but the pilot will be in a normal flight condition and able to control the plane. If he or she stalls the airplane, but the ball is centered and there is no yaw present, it will be a normal stall; decreasing the angle of attack and adding power will remedy the situation.

Go back and read that last paragraph. It says that in every accident involving a spin, pilots did not one but two things wrong. Also, given the benign nature of most modern airplanes, they didn’t just induce a little yaw and get a little slow, they had lots of yaw and were very slow—modern airplanes simply won’t spin unless forced to by extreme combinations of slow speed and yaw.

Is taking a student up to altitude, pulling into a nose-high stall, then kicking into a spin going to prevent accidents? Of course not, because that’s not the way stall/spin accidents happen. To understand what’s really happening, let’s look at the two contributing factors—speed and yaw—one at a time, then set up a realistic teaching and learning scenario.

For an airplane to become slow enough to stall, the airspeed must be allowed to fall a long way. Even though the rule-of-thumb approach speed is 1.3 stall, most POHs and most instructors and pilots fly faster than that. A C-172 POH, for instance, gives a full-gross, flaps-down stall speed of 44 knots, and 1.3 of that would be 57 knots. The POH, however, says approach should be 55 to 65 knots. How many pilots do you know who fly it at 55 knots, or even 65 knots? Pilots universally fly too fast, so how are they managing to get the airplane too slow? In this case, the pilot has to lose 23 knots to stall the airplane—23 knots! What the heck are pilots looking at to allow that to happen?

Part of the reason the airspeed degrades is that the pilot is distracted by something and isn’t cross-checking the airspeed. However, something even more basic underlies this entire scenario and lets the stall happen.

An airplane is unlikely to stall unless the nose comes up and stays up for a relatively long period of time. It won’t just bob up for an instant and stall the airplane. It has to come up and stay there long enough for the speed to bleed off. In every stall/spin accident, the nose had to have been visually much higher than normal for a period of time or the stall wouldn’t have happened. But the pilot didn’t see that the nose was high because the nose wasn’t part of the normal scan. The pilot was using the airspeed indicator as the primary speed control and when distracted, the pilot didn’t check it as often as required. Then the nose came up without the pilot seeing it and the airplane stalled.

Here’s another absolute truth: A pilot who’s aware of his nose attitude at all times will never accidentally stall an airplane—never!

There’s an extenuating circumstance to the above. When most airplanes have full flaps down, especially Cessnas, the nose doesn’t have to be brought above the horizon to precipitate a stall. In practice stalls, however, 100% of the time the nose is well above the horizon and the pilot is pulling, pulling and then pulling some more. Finally, it buffets and the instructor says, “Okay, that’s the stall buffet. Recover.” That’s not the way stalls happen in real life. Extreme nose-high attitudes are nearly impossible for even the most poorly trained pilot to miss. It’s the subtleties of letting the nose drift up to a nearly normal-looking attitude in a full-flap condition that catches them unaware.

When was the last time you did a stall with lots of flaps and the nose on, or even slightly below, the horizon? Try it. You’ll be surprised.

And then there’s the yaw factor. When it comes to spins, we have to inject a little reality here. An airplane won’t spin with the ball barely peaking out of its hole; it has to be way off center. In a modern airplane, simply using bad coordination in a turn isn’t going to give that much yaw. In fact, even in a hard turn with no rudder, a Piper or Cessna’s ball barely slides out of center. So, how is the ball getting far enough out of center to cause the airplane to spin when it’s also stalled? The problem usually begins with the ailerons and is then compounded by the rudder.

It comes as a surprise to some pilots that the ailerons can make the ball move, too. What little coordination training most pilots receive is usually rudder-oriented: “Step on the rabbit as he comes out of his hole.” If they think of centering the ball at all, they usually think only of their feet.

If you want to try something interesting, slow your trusty airplane down to approach speed, or a little below, and crank in a lot of aileron with no rudder and look at the ball. As an airplane slows down and the angle of attack goes up, the adverse yaw always gets worse. So, if you’re slow and moving the ailerons without rudder, the ball is even more willing to slide in the direction the ailerons are moved.

So what? The aileron drives the ball off center. What’s the big deal? You’ll get the idea when we set up a traditional stall/spin accident.

Most of these accidents happen on the base-to-final turn. Let’s say you, the pilot, have the flaps down and you’re late making the turn onto final and you overshoot. As you crank into the turn to come back to centerline, you realize you’re getting more bank than you’re comfortable with, so you put some outside aileron in to hold the bank. This opposite aileron drives the ball to the outside of the turn, but also slows down the turn. To tighten the turn and get the nose around more quickly, you feed in rudder in the direction of the turn. This drives the ball even farther to the outside. Let’s say it’s a left turn, so you have right aileron to hold the bank and left rudder to keep the turn going. This won’t hurt you as long as the speed stays up.

The very fact that the airplane is in a turn raises the stall speed, but crossing the controls spoils some lift and further increases the stall speed. So, even if the nose stays down, the margin between you and stall speed has decreased. Furthermore, because of the decreased lift, the nose wants to go down, so some back pressure is applied to keep it from falling. A really bad situation is in the making!

In the usual accident scenario, this is the moment when the pilot is distracted and lets the nose continue rising. All you have to do is see that nose creeping up and you’ll stop it and save yourself. But you’re not used to the finer points of attitude control and don’t realize the crossed controls have aggravated the situation and the airplane will stall long before the nose comes close to the exaggerated attitudes you’ve seen during stall practice. The nose tells you what’s about to happen, but you simply don’t see it.

With the flaps down, the stall is more abrupt and when the airplane unloads, it starts to roll over the top. Unfortunately, as the airplane stalls and rolls, most pilots will instinctively slam in even more opposite aileron, which further stalls the inside wing, making the airplane whip into the first turn of a spin. As a normal rule, the airplane is too close to the ground to complete even a full turn, much less two turns, so knowing how to recover from a developed spin is of little use.

The foregoing is the operational situation in which spins should be taught. Spins need to be put into the context in which they actually happen. Not in some phony-baloney, nose-high-and-stomp situation that doesn’t reflect reality.

Teaching spin prevention, however, is highly complicated by some POHs, which prohibit spinning with the flaps down. The POHs often make that prohibition not because the flaps will adversely affect the spin, but to prevent flap damage if the airplane is oversped during the recovery. So, even with an instructor on board, the exact scenario that’s killing people can’t be prepared for. This does not, however, prevent an instructor from flying the airplane right up to the point of departure and recovering before the spin is entered, which is the goal of the instruction anyway.

This type of training is further hampered by an FAR that says when spins are being taught to CFI candidates, no parachutes are necessary. However, if spins are being taught to a non-CFI candidate (a normal pilot or commercial student), parachutes must be worn. We contacted three reputable pilot academies, which, combined, train thousands of students each year, and not one had as much as a single parachute. So, even if a student wanted true spin training, the academies couldn’t and wouldn’t give it, nor do they have any interest in doing so. They could, however, do stall/spin recognition training and not need the parachutes.

What conclusions can we draw? First, we don’t actually need spin training to prevent spins. What we need is an aggressive program to make pilots more aware of their nose attitude and what the ball is doing at all times. We need to educate them to feel what the airplane is doing. It’s simple attitude control and coordination—nothing more complicated than that.

If we’re going to teach actual spin recoveries, let’s teach them in a realistic base-to-final turn situation. Pilots need to see how quickly some airplanes, the C-152 being the most dramatic of the bunch, lose speed and snap over the top during a cross-controlled stall. Let them see how subtle that speed bleed-off can be and how far the ball goes off center when they try to hold a bank with aileron yet force the nose around with rudder.

There’s an old axiom that fits this subject nicely: “If you’ve never been there before, will you know how to find your way back when you find yourself there?” Some of us think everyone should be put “there.”

The next time you read about a stall/spin accident, think back to the last time you overshot final. Did you power up and go around or did you cheat with the rudder and aileron? Then think about how lucky you were.





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