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Flight Control Failures

These problems seldom happen, but this is how you handle them

By Jeff Pardo

Next to an in-flight fire, control surface failures rank pretty high on the list of things that tend to put pilots on edge. Even the best preflight might not immunize you from experiencing a control surface failure, but knowing what to do and taking prompt action will prevent one from ruining your day. Although control-surface failures are rare, they can come in several rotten flavors, depending on whether it happens to your ailerons, rudder, elevators, or flaps. Let's have a look.

Airplanes have fixed appendages, but it's the hinged control surfaces on their wings and tail feathers that allow them to climb and maneuver in three dimensions with precision. These surfaces are connected to the cockpit controls by a system of steel cables and pulleys, or by pushrods and bellcranks, hidden in the nether regions of the fuselage. Although the actuating mechanisms that relay control inputs out to our airplanes' extremities are largely hidden from sight, we know they've been well-designed, and for the most part, we're satisfied with checking just the hinge pins, counterweights, and other exposed moving parts when we preflight control surfaces. Short of turning every preflight into a 100-hour inspection, we'd have to be.

The fact is, however, that it's not all hermetically sealed clockwork in there. Stuff happens. While our airframe and powerplant mechanic's back is turned, something can snag, fray, disengage, or otherwise compromise our presupposed evolution beyond wing-warping, weight-shifting, blowing real hard, and prayer. For example, an uncommanded roll can quickly develop into an unusual attitude, and an airplane without an effective rudder has little defense against a spin. Supposing a crimp slipped somewhere, or a cable went slack and came off one of the pulleys. Or suppose that some small foreign object slides around and jams a pushrod. Think it can't happen? Although uncommon, it can. And our defense is preparedness, recognition, and prompt action. Let's take a look at each of the various types of control surface failures, one at a time.

Remember your first flight lessons. You turn the control wheel clockwise (or push the stick to the right) to enter a right turn, which moves those ailerons near your wing tips. The left one goes down; the other goes up. The aileron deflected down increases lift; the one deflected up does the opposite; and the airplane rolls to the right about its longitudinal axis. Along with that increased lift on the southpaw side comes increased drag, and the airplane wants to actually yaw to the left about its vertical axis. That's the adverse yaw you learned about in ground school, and to counteract it you gently press the right rudder pedal, moving a hinged surface at the rear of your vertical stabilizer towards the right, which brings the nose back toward the right in a coordinated turn. So we smoothly coordinate our turn...uh oh, wait a minute; something's stuck. The ailerons are jammed! OK...let's see...they say don't panic. Just "fly the airplane." Well, OK, but how?

Control failures are manageable as long as you take prompt action before an unusual attitude develops. As you recall, manipulating the ailerons causes a yaw, which you counteract by applying rudder. And when you use the rudder it induces a roll, which you check with ailerons. Can you say "slip"? We can all say it, but some of us may be unsure just how to begin one. Slips are a wonderful tool, and here are the three magic words to help you forever remember how to do one: Kick top rudder. ("Top" implies that you lead with an aileron roll, then when you have a "top" rudder—that is, it's rolled enough that one side of the plane is beginning to point upward—stomp. Presto!) One of several important rules: Fly gently. No sudden lurches, please. If it's the ailerons that went AWOL, you'll have an uncommanded roll. Just step skyward into a slip. That's how you'll maintain directional control. If the rudder is the problem, do the reverse and enter a forward slip instead with ailerons, to oppose the rudder. You'll need to add more power, and watch your altitude.

Try a momentary flick of aileron control to dislodge any foreign object. Make all turns toward the low wing. Let air traffic controllers know about your problem. Your next concern is getting down. If your home aerodrome's runway isn't at least 4,000 feet long, go somewhere that is. Last, but not least, land on a crosswind runway against the slip. Flying cross-eyed like this isn't pretty, but it beats making the Metro section of the newspaper. You can't practice breaking your airplane, but learning about slips might pay off big time.

Next, let's tackle a recalcitrant elevator. Those hinged things at the rear of your horizontal stabilizer are connected to your control wheel (or stick) and are your primary means of pitch control. It's the action of the elevators going up and down that makes the houses get smaller, or bigger. Get it just right, and you grease that landing. Lose them, and the houses can get very big, very fast.

In the case of an elevator failure, you have three weapons at your disposal. You can alter your center of gravity somewhat, depending on how much junk you're hauling around and whether anybody is up there with you to help out. You can use power changes, too. Most airplanes will pitch up with added power; controlled use of the throttle might do it alone. And then there's the blessed trim tab. That's the "elevator within the elevator," which is your best bet to save the day. Use a delicate touch. Consciously remind yourself to fly gently, restricting your envelope to a very few degrees of pitch. You have just become a test pilot, so think like one. One thing definitely in your favor here is that design criteria (for singles, anyway) require that they can be landed without any primary pitch control.

Like they always say: First, fly the airplane. You probably still have control in the other axes, so fly them gingerly. That trim wheel (or electric trim switch) just became your best friend. And again, although there's "no place like home," if home means a 2,700-foot runway, don't go back there—point yourself instead at the longest runway that you can find nearby. Third, get on the radio and shout a "mayday!" on whatever frequency you're on; if you're not talking with ATC, make the call on 121.5 MHz and dial in 7700 on the transponder.

There are two types of elevator control failure: when the cable breaks or comes loose altogether, and when it jams. If it's gone loosey-goosey, the elevator will be free-floating and you will use the trim wheel just like you do in regular flying. Imagine that the wheel is your airplane. You'll pitch in the same direction you make it spin. If it's jammed, the trim tab itself will become a baby-sized elevator and control should be reversed, though the looseness in non-pushrod systems may allow only minimal control. It's up to you to quickly and gingerly find out which brand of failure you've got. (The airplane will also tend to continue flying at whatever speed it jammed at, if you do nothing.) While still at altitude, apply a brief forward-and-back jab or two on the stick or control wheel if you've got a jam. Things just might get less sticky. Lastly, make a shallow approach to that two-mile runway. Do not use flaps! (Pitch is very sensitive to flap position.) Ground effect usually induces a nose-down pitch, so be prepared to use small power changes (and trim) to cushion your landing.

The last type of control surface misbehavior involves the flaps. Flaps aren't essential for flight, but they sure make some parts of it easier. Those downward and backward extensions to the inboard trailing edges of the wings might be hydraulically, electrically, or manually operated and serve to increase lift when partially extended by increasing the wing's surface area. When fully extended, flaps mostly add drag and allow a steeper and slower approach.

Flaps can fail in three ways. They can refuse to come down, which should be a nonevent—just don't try any short-field landings. If they're fully extended and they refuse to retract, and you haven't taken off, stay on the ground. If they refuse to retract in flight, adding power should help you return to the runway and land. Aircraft certification requires a 2-degree go-around climb with full flaps at sea level, gear down, and takeoff power, but an older airplane on a hot day might just hold altitude.

It's the third type—split flaps—that'll really get your attention. A split flap situation can come about because of a linkage malfunction deep inside your wing, or because a roller bearing wears just enough to lock up in its track and jam one flap in the down position, while the other one comes up. One flap down, just like a lowered aileron, will result in a sudden roll moment. It's alarming, to say the least.

Preparedness can help to prevent split flaps; check every movable part for signs of excessive wear and proper range of motion, including bearings, tracks, and linkages. And never lower or raise your flaps in more than 10-degree increments while in flight. If you can, visually check to verify that you got what you asked for. Flaps split by 10 degrees are relatively easy to deal with; 30 or 40 degrees is another matter.

First, fly the airplane—gently. And again, don't panic. An asymmetric lowered flap will cause a roll moment away from it, and an adverse yaw moment toward it. Why the roll? Because lift just increased on that side. Why the yaw? Because of the drag, of course. What's the remedy? Simple: Just counter the roll with ailerons, and use that rudder to keep the nose straight ahead. (If you're in a twin-engine airplane, you can also use asymmetric power.) Using the ailerons is instinctive; it's the opposite rudder and a slight slipping condition that needs some forethought. Then, head toward a nice long runway, and if it's even a little dicey, declare an emergency and squawk 7700. The thought of split flaps should be enough to make incremental flap application habitual.

Keep all these things in the back of your mind. Although they're not common, control-surface failures can happen. Here's to hoping that you never need to use this information.

Jeff Pardo is an aviation writer in Maryland with a commercial pilot certificate for airplanes, and instrument, helicopter, and glider ratings. Flying since 1981, Pardo has been a mission pilot in the Civil Air Patrol and for AirLifeLine.