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Flap Failure -- It Happens

A careful preflight won't protect you from some problems -- in the case of a flap problem though, that’s not necessarily the case. Knowing what to look for (and what to do if it happens anyway) can make the difference between a tough day and a bad year -- or no year.

A careful preflight won't protect you from some problems -- in the case of a flap problem though, that's not necessarily the case. Knowing what to look for (and what to do if it happens anyway) can make the difference between a tough day and a bad year -- or no year.

BACKGROUND
Flaps aren't essential to flight, but they sure make some parts of it easier. Those downward and backward extensions to the inboard trailing edge of wings might be hydraulically, electrically, or manually operated. They serve to increase lift when partially extended by increasing the wing's surface area. (The big boys use similar articulating panels on the leading edge, too, called slats.) When fully extended, flaps mostly add drag and allow a steeper, slower approach.

INTRO
Flaps can fail in three ways. (Two of them I don't really consider failures ... just malfunctions.)

  1. They can refuse to come down, which should be a non-event. (Just don't try any short-field landings ... and be ready to sit up real tall to see over the nose.)
  2. If they're fully extended and they refuse to retract, and you haven't taken off, you've no business trying. If they refuse to retract in flight, you have the option of adding power if you need to do so to return to the runway, announcing your problem, and landing.
    NOTE: Aircraft certification requires a two-degree go-around climb with full flaps at sea level, gear down, and takeoff power. (An older plane on a hot day might just hold altitude, though.)
  3. It's the third type, split flaps -- that'll really get your attention.

PROBLEM
A split flap situation can come about because of a linkage malfunction deep inside your wing, which no preflight would preclude. It can also be because ... say, in the case of a Cessna single ... a roller bearing wears just enough to lock up in its track and jams one of your flaps in the down position, while the other one comes up. This does happen. In fact it happened in my flying club this past summer. One flap down, just like a lowered aileron, will result in a sudden roll moment. It's alarming, to say the least.

NOW THE LOGISTICS
First, fly the airplane -- gently. And, don't panic. An asymmetric lowered flap will cause a roll moment away from it, and an "adverse" yaw moment towards it. Why the roll? Because lift just increased on that side. Why the yaw? Because of the drag, of course.

DEFENSE
Three things: preparedness, recognition, and prompt action. Part of preparedness in this case is mitigation: during the preflight, check every movable part for signs of excessive wear and proper range of motion. That includes bearings, tracks, and linkages. And avoid lowering or raising your flaps in more than 10-degree increments while in flight! Always look over your shoulder to verify you got what you asked for. Ten-degree split flaps are relatively easy to deal with ... 30 or 40 is another matter. (Again recognition is the easy part here. You'll know something's wrong!)

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, 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.

BOTTOM LINE: Split flaps are scary. Preflights can help, and incremental flap application will, too. But in the end, knowing what to do is going to save you.

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