Originally published January 1993
Broken Mixture Control
Broken Propeller Control
Broken Throttle Control
Broken Elevator Control
Rudder or Aileron Failure
All of us can remember those fun times while learning to fly when you sadistic instructor reached over, pulled the throttle to idle, and waited to see what you would do. And of course, just pushing the throttle back up where it was, slapping your instructor's hand, and telling him "Don't you ever do that again!" was not an acceptable solution. The point of this part of your training was to force you to practice your response to a simulated "emergency."
Until airplanes are perfectly reliable and weather is no longer a factor (don't expect this in your lifetime), occasionally we are all going to have some kind of in-flight emergency. Some of these are critical and will have grave consequences to you or your aircraft if not handled properly, such as when the engine stops and you find yourself reading the Sensenich logo on your propeller in the sudden quiet. Usually these types of emergencies are covered in the Pilot's Operating Handbook for certified aircraft. The procedures are pretty much the same for homebuilt aircraft, so I won't rehash them here. Hopefully you run that kind of thing through your head on a regular basis anyway.
Other minor failures are covered in your flight training, such as what to when your radio fails. In fact, most aircraft (if not all) can be safely landed in VMC with a total avionics failure. If you don't think you can do that, maybe you should give your CFI a call.
Instrument rated pilots have already been beaten over the head about how to continue the flight safely after half the instrument panel has taken a holiday. I won't cover that here since a) I'm not instrument rated, and b) You can easily find a better discussion in an instrument ground school text or with your local CFII.
Now that we know what I'm not going to discuss, what am I going to discuss? Learning to fly an airplane is a process of learning to manipulate various controls in the cockpit. We come to assume that these controls will always work as expected, but what do you do when they don't? This is the subject of this article. Why did I decide to write this? The idea came to me after successfully recovering an airplane with a broken mixture control.
But first, in the absence of sweeping tort reform, we bring you this word from my lawyer:
The following thoughts are my own, and have not been endorsed by the FAA or your airplane manufacturer. They are presented simply to help you determine your own procedures.
Besides, it's better to think about these things now in the comfort of where ever you are, rather than when you're plunging earthward with no clue what to do. If you had a really good CFI, you may have already thought about some of these.
You will probably notice this problem when you try to lean the engine for cruise and the mixture lever or knob gets all the way back to idle cut-off with no increase in EGT and no decrease in RPM. This could be caused by a break at either end of the cable, or somewhere in the middle of the cable. If the break is in the middle of the cable, you may still be able to move the mixture to full rich by pushing in on the control, but you will not be able to lean the engine. This is okay, since most aircraft land at full rich anyway. If the break is at the cockpit end of the cable, you may be able to grab the cable and move it without the lever.
By the time you find out about this problem, you will probably not know where the mixture control at the carburetor is set (unless you can tell by looking at your EGT). There are three likely possibilities, which could change from one to another at any point:
1) The mixture control has leaned to idle cut-off. The sudden quiet and the Sensenich logo should be your first clue on this one.
2) The mixture control is at full rich. This is not a big problem, since this is where you normally want it for landing. Unless you know definitely where the break in the cable is, go ahead and move the control to full rich. The broken cable inside the sheath may still be able to push the mixture to full rich. Realize that you will have a higher than normal cruise fuel flow, and there may be a reduction of power.
3) The mixture control is still where you last leaned to. You will be fine as long as you stay at or above the altitude where you last leaned the engine. When you descend, there is a chance that your engine will become over-leaned by the increasing air density. This could cause over-heating or, at worst, engine stoppage. For this reason, plan a higher than normal approach, such that you will still be able to make the runway, even if the engine quit at any point.
Applying full carburetor heat (if so equipped) will also enrichen the mixture. If you don't remember why, go back to your ground school texts and review. It's one of those questions you studied at one time.
After a successful landing, you can stop the engine by turning off the mags, but realize that the engine may continue to run (diesel) for a while, and there will still be fuel in the engine.
First off, if you have a fixed pitch propeller, you can skip this section. Second, if your flight manual has a recommended procedure for this emergency, follow it.
The cause of this problem could be a broken cable, as detailed under Broken Mixture Control, or a malfunction in the propeller. Either way, the result to you is the same--you have no control over propeller RPM.
Again, if this happens to you, one of three situations are likely, and can change at any time:
1) Runaway Prop (Overspeed). The blades have decreased in pitch, and may have gone all the way to flat pitch, and thus cannot produce the blade drag to offset the engine torque. The immediate action required is to retard the throttle until the RPM is back within limits. If the overspeed continues, the prop may shed a blade, followed shortly by the engine and its unbalanced propeller. This is real BAD, since you will now have a severe unrecoverable aft c.g. problem. Don't worry about missing the next EAA meeting at this point, because you'll be missing most everything. Once you have the RPM within limits, determine if you can still maintain level flight. If you can, you can decide if you want to try to make the next airport on your sectional (or follow your GPS guidance to the nearest airport). Be alert at all times, because your situation might get worse, and you may have to make a power off landing anyway. As before, make a high approach, ready at all times to totally lose all thrust.
2) The prop is stuck at its last setting. This is okay, as long as the RPM doesn't change. Try to increase the RPM to the landing RPM, as the push-pull cable may still push but not pull. If you cannot increase the RPM, you can fly the approach at cruise RPM, but realize you may not be able to go-around, so avoid as much as possible any need to go-around. Plan the high approach, alert for engine failure at any time.
3) The prop feathers or partially feathers. The blades have increased in pitch, and the RPM drops. If prop RPM cannot be increased, check if there is enough thrust for level flight. If not, look around for that landing spot and follow your loss of engine power emergency procedures. If you can maintain level flight, follow the same approach procedures detailed above.
Another possible case of a broken cable. You may be able to increase the throttle but not retard it if your push-pull cable has become just a push cable. If the engine goes to idle, it's engine out landing time. If the engine stays at cruise power or higher, you should be okay until time to make the approach. Of course, it could change to idle at any time, so be ready for that engine out landing. For the approach, you can descend at higher than normal speed, but be careful you don't exceed your aircraft's speed restrictions.
Eventually, though, you will need to slow down. You can still slow down the engine by over-leaning it with the mixture control, but this is pretty much an all or nothing proposition. Don't pull it all the way back to idle cut-off, or you'll be staring at that Sensenich logo. Likewise, don't cut off the mags if you don't have to, because once the engine stops, you may never get it going again. The engine may start to overheat if leaned for too long, but this will probably be the least of your worries at this point.
The cable to the elevators snaps, or the push-pull rod breaks. As long as the elevator doesn't get stuck in a hard over position, you have a decent chance of getting down in one piece.
The first thing to check is if the pitch trim still works. If it does, simply use the trim to control your pitch. Make small inputs, and think well ahead, since this method of pitch control is not as quick or responsive as the yoke or stick. You RV-6 guys have it made here, since the pitch trim is very effective. However, it is also sensitive, so remember the small inputs. If you're flying an aircraft with marginal nose-down trim at cruise speed, you may need to slow down some so that the trim will be effective.
If the pitch trim isn't working, does your airplane have a noticeable pitch trim change with flap extension. You may be able to control your pitch trim with the flaps. The original Kitfoxes used this method for normal pitch trim.
The throttle can also be used to an extent to control pitch. Unless you're flying your F-16 or your X-29, adding power will climb the aircraft, pulling power will dive the aircraft. This is how the DC-10 that crashed in Sioux City with total flight control failure controlled its pitch. The drawback is that if this is your only method of controlling pitch, you probably won't be able to slow to landing speed. You'll be stuck with a Navy landing of flying the airplane into the ground (hopefully at a very shallow angle).
In any case, plan a shallow, stabilized straight-in approach, with minimal maneuvering required. Remember that the pitch change to flare is significant, so be ready for it. Also, be extremely careful not to over-flare and balloon. If you do, by all means, go-around and try it again.
This is not really a big problem, as long as one or the other is still functional. If the ailerons are working, ignore the ball and make uncoordinated turns. If the rudder is working, simply roll with the rudder (rudder turns).
Look for a runway with little to no crosswind, if possible, since you won't be able to slip (wing-low method) without both controls. Consider flying in a crab all the way to the runway if necessary. Also look for a straight-in approach with minimal maneuvering.
Total loss of flap control is not too serious. Simply make a no flap landing, which will no doubt be faster and shallower than normal.
Split flaps (one flap lowered more than the other) can be very bad, as you may not have enough aileron control to overcome the rolling moment. If, while moving the flaps, you notice an uncommanded roll, stop the roll if possible with the ailerons, and move the flaps back to their original position before the problem. If they were up, put them up. If they were down, put them down. Leave the flaps there, and proceed with the landing as appropriate for the flap position.
This article is intended to get you thinking about possible failure modes in your aircraft that are not covered in your Pilot's Operating Handbook. These are all of the ones I could think of, but your aircraft may have others. I encourage you to consider each system on your aircraft and ask yourself "What would I do if this system failed." Some answers will be that your time has come and you won't be able to do anything about it. These areas should be checked regularly to minimize the risk of such a thing happening. Other answers will be as simple as if the clock stops working, use your wrist watch. Many other failure modes will fall between these two extremes, and it's better to think about it now while safely on the ground rather than after the failure occurs. At that point, it may be too late.
Contents of The Leading Edge and these web pages are the viewpoints of the authors. No claim is made and no liability is assumed, expressed or implied as to the technical accuracy or safety of the material presented. The viewpoints expressed are not necessarily those of Chapter 1000 or the Experimental Aircraft Association.
Revised -- 22 February 1997