Plane & Pilot
Tuesday, December 20, 2011

Landing Without Flight Controls


Under some conditions, it’s possible to land an airplane without using normal aerodynamic controls


Schiff also made the point in his video that it's possible to fly an airplane with a pitch control that only functions in one direction. The elevator is controlled by two cables, one for up and one for down travel. If a cable breaks, you'll normally lose the ability either to pitch down or to pitch up, but not both. That means if the up cable fails, you could trim the nose full back and hold the nose forward with the yoke, adjusting forward pressure as necessary to maintain aircraft control. Pretty obviously, you'd do the opposite if the down cable failed.
I'd wait until she had the elevator perfectly trimmed; then I'd ease forward or back in the seat just enough to cause the airplane to slowly pitch down or up.
If you have cowl flaps or vents that open into the wind, you may find that they also can affect pitch. My Mooney has a large overhead cabin vent that improves airflow through the roof, but requires a very slight amount of down trim when fully open (and yes, it costs me about a half knot of cruise). Conversely, open cowl flaps induce a slight nose-down moment that requires half a knuckle of up trim (and subtracts another knot).

Loss of rudder and aileron control are a little more problematic, though again, the condition isn't insurmountable. Aircraft with openable windows or doors on each side have an advantage in that an open window or door can deflect the relative wind and induce a turn in that direction. Add throttle and trim to manage altitude and pitch, and you might be able to fly the airplane with no elevator, rudder or aileron control. Remember, however, that an open window or door also is liable to affect pitch, most often with a down moment. You may need to adjust power and trim to offset the extra drag.

Asymmetric control failures can present special problems. Split-flap situations can be among the worst of all control-failure nightmares. A linkage malfunction inside the wing or a worn roller bearing that locks up, jamming one flap in the down position, can cause one flap to remain full down while the other retracts. Such failures are the best arguments for extending or retracting flaps in increments of 10 degrees, checking to make certain what you asked for is what you got, then continuing.

The ideal solution if there's a problem and you can get the flaps back up is to simply make a no-flap landing. Alternately, set both flaps to full down, not an optimum choice until you're on short final, but again, not usually an uncontrollable situation.

The worst combination is to land with one flap fully extended and the other full up. Some aircraft may be only marginally controllable in that configuration. A totally split-flap situation is so uncommon that the FAA has no certification requirements to counter it.

Speed brakes that extend asymmetrically or refuse to retract are most often not a major problem. In the one-up-one-down scenario, opposite aileron should easily overpower the opposing spoiler, and a full extension on both sides that won't retract normally isn't a problem, either. The FAA demands that speed-brake manufacturers demonstrate the ability to fly and land normally with one up and one down.

Landing with speed brakes fully extended is hardly a challenge. As the name implies, speed brakes are intended to help brake speed and/or lose altitude, and they're most effective at higher Mach numbers. Speed brakes become progressively less effective at lower approach velocities. Most general aviation aircraft don't manifest any adverse control problems at all from a deployment that won't retract.

Whatever the failure, remember that you may need the longest, widest runway available for your return to Earth. That may preclude landing back at home base, especially if the longest or only runway is 2,500 feet. Better to pick the most comfortable runway you can find, and don't even think about using flaps. They can induce pitching moments you may not be able to countermand. Land with as flat and gentle an approach as possible to minimize the pitch change at the bottom.

The main considerations in the event of a control jam or failure are never to give up or stop thinking. If you throw up your hands in frustration and submit to panic, the airplane very well may become a lawn dart.





2 Comments

Add Comment