There’s a big problem with general aviation autopilots. Even though the number and sophistication of autopilots seem to be increasing at a steady rate, many pilots don’t seem to have a complete understanding of how to operate them. Or take full advantage of all their capabilities. That may sound odd, but consider that some of today’s modern training fleets have newer airplanes, many of which are equipped with autopilots. Consider also that many flight instructors don’t teach autopilot usage. Autopilot operations either aren’t in the curriculum, or instructors may feel that their teaching time is better spent dwelling on the basics. That, or they don’t understand autopilot operations themselves.
The result is that a lot of pilots out there are flying with autopilots they don’t fully understand. In this occasional series, we’ll talk about autopilot operations in both general and specific terms. The goal: to become more autopilot-aware.
We’ll sort of back into our autopilot discussions by working in reverse. This time, the subject is how to turn off the autopilot. Why the emphasis on disabling such a useful piece of gear? Because if a control or other problem occurs, the outcome may depend on your understanding the many ways you can cut the autopilot out of the loop.
When would you want to quickly disengage an autopilot? Here are just a few scenarios:
- Upon encountering moderate or greater turbulence
- In case the pitch trim runs away
- In case the autopilot follows false, or improperly entered, navigation cues
- In airplanes with slaved compass systems, if the slaving fails
- When the autopilot won’t hold a heading
- When the autopilot malfunctions for any reason
- When entering large-droplet icing conditions
- When making a momentary off-course heading change
- Prior to landing
Depending on the system you’re using, there can be up to nine different ways of disengaging an autopilot. That’s good, because if one method doesn’t work you can move on to an alternative. However, each method carries certain operational implications. In order of preference, here’s a sampling of the ways you can kick your autopilot offline:
Push the autopilot’s control-yoke-mounted cutoff switch. Usually colored red, and usually located at the top of the left horn of the pilot’s control yoke, this switch is the handiest way of cutting the autopilot out of the loop. Like any other time you disengage an autopilot, you ought to hear a series of beeps or tones after you hit this switch. This is the aural indication that the autopilot’s been disabled. Some installations let you mute the beeps, so the passengers won’t be alarmed.
Turn the autopilot switch to the Off position. Using the autopilot’s own switch, simply turning off the unit ought to do the trick. This switch may or may not be colocated with the autopilot’s control panel function selectors. Depending on the model, it could be anything from a largish, paddle-shape switch on a center pedestal to a small toggle switch situated well away from any other autopilot controls or annunciators.
Pull the autopilot circuit breaker. If the autopilot’s power switch didn’t do the job, then pulling its circuit breaker should be tried. It’s a good idea to mark this circuit breaker’s location, or fit it out with a circuit breaker "collar" so that you can easily find it in the heat of a tense moment, or at night.
Pull the pitch trim circuit breaker. This is another circuit breaker that should be clearly identifiable. In autopilots that work with electric pitch trim, pulling this breaker should stop a runaway pitch-trim condition. With many two-axis autopilot systems, pulling this breaker will also cause the autopilot to disengage. Of course, you’ll have to manually trim the airplane with this breaker pulled. With a runaway pitch trim condition, you’ll want to have a firm grip on the control yoke before you pull this circuit breaker. That’s because you could be presented with vigorous out-of-trim pitch force requirements; if you want to maintain control of the airplane, be prepared for some hefty pushing or pulling, and a lot of retrimming with the manual pitch trim wheel. The pitch-trim circuit breaker should also be pulled whenever the electric pitch trim is running too far for the current or commanded flight condition. The trouble here is that you may not be aware of an imminent runaway—unless, like many business jets and Transport-category airplanes, you’re fitted out with a trim-in-motion alerter. With these, you’ll hear a beeping or other tone whenever the pitch trim is in motion. If you hear it running too long, then you’ve had fair warning.
Activate the yoke-mounted electric pitch-trim switch. In some systems, this disengages the autopilot. In this sense, the yoke-mounted trim switch serves the same function as the red yoke-mounted autopilot cutoff switch. You’ll still be able to trim the airplane electrically, but the autopilot kicks off. Check your pilot’s operating handbook for the final word on your system’s electric pitch trim functions and procedures.
Push, and hold down, the control wheel steering (CWS) or touch control steering (TCS) button. These buttons are found on the control yokes of many sophisticated airplanes with two-axis or three-axis (i.e., with integral yaw damper functions) autopilots. Whether labeled CWS or TCS, the purpose of this switch is the same: to momentarily disengage all functions of the autopilot while you hand-fly the airplane. You might need this feature to avoid nearby traffic or perform a quick course interception. CWS/TCS lets you do this without the hassle of fully disengaging the autopilot, then reprogramming it. Think of it as an autopilot-interrupt switch. The downside is that to keep the autopilot disengaged you have to keep pressing down on the button. If you release pressure, the autopilot snaps back into action. So CWS/TCS can be a useful first step in disabling an autopilot, suppressing its functions while you hunt for the circuit breakers we mentioned earlier.
Turn off the avionics master switch. This is a drastic measure, because you’ll lose all your avionics (transponder, communications radios, and every piece of navigation equipment) and probably your electric pitch trim. On an IFR flight plan, that means that lost communications procedures will apply, so the avionics-off option requires that you tell ATC before you do it and advise them what your immediate plans are. It’s difficult to imagine a situation where such a measure would be justified, except perhaps in cases where the excessive heat of a malfunctioning component caused it to fail operational or, of course, in the case of an avionics-induced fire.
Turn off the main master switch. Like the previous measure, this is a desperate effort. Using this solution, you’ll lose all the electrical equipment on the airplane, from pitot heat to map lights to everything in between.
Physically overpower the autopilot’s control inputs. While you often hear that it’s possible to overpower a misbehaving autopilot, this is a last-ditch procedure that deserves careful consideration. Yes, you can overpower an autopilot. No, it shouldn’t be your first response, which is why this option appears last. Why? Because the autopilot will probably try to counter your control inputs, interpreting them as uncommanded changes in pitch or roll—changes that require more and more pitch or roll inputs on the autopilot’s part to overcome. This faulty feedback loop can leave you with a severely out-of-trim airplane at a very bad time. Let’s say you’re flying with an autopilot with an altitude-hold feature and enter severe turbulence or inadvertently penetrate a thunderstorm. The airplane enters a strong updraft and starts to climb. The autopilot will try to command the airplane to return to the original altitude, which means that the pitch-trim wheel runs nose-down. You, meanwhile, are trying to ride out the bumps and haul back on the yoke in an attempt to nail VA (maneuvering speed) or simply to prevent your airspeed from rising to a dangerous level. The autopilot senses your inputs as an even stronger "updraft," and the trim wheel spins nose-down even more. Let go of the yoke now, and you’re headed downhill in very, very short order. You get the idea.
Knowing how to operate an autopilot is important. It’s a useful work load-saving device that relieves fatigue and can improve situational awareness. But the importance of knowing how and when to disengage an autopilot can’t be overemphasized. You typically turn autopilots on when you’ve climbed away from the departure airport and are en route to your first fix, in a more or less calm environment. When you need to turn them off quickly, all hell is breaking loose. Suddenly, last things come first, and you simply must know how to take the autopilot out of the picture with a minimum of fuss.
Links to additional information about autopilots may be found on AOPA Online ( www.aopa.org/pilot/links/links0006.shtml). E-mail the author at [email protected].
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