Thursday, 26 January 2017
WHAT DO I DO AFTER I SAY "Oh, *@#%!!"?
Acknowledgements: Russ Erb/EAA Chapter1000
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 was to force you to practice your response to a simulated "emergency." Usually these types of emergencies are covered in the Pilot's Operating Handbook, so I won't rehash them here. 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.
Learning to fly is a process of learning to manipulate various controls in the cockpit. We assume that these controls will always work as expected, but what do you do when they don't? The following thoughts have not been endorsed by the FAA or your airplane manufacturer, and are presented without prejudice to help you determine your own procedures in the comfort of wherever you are now, rather than when you're plunging earthward with no clue what to do.
You will probably notice this problem when you try to lean the engine for cruise and the mixture lever 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 in the cable. If the break is in the middle of the cable, you may be able to move the mixture to full rich by pushing in on the control, but not 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 carburettor is set. 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 propeller logo should be your first clue on this one! Institute engine-out procedures
2) The mixture control is at full rich. This is not a big problem, since this is where you normally want it for landing, but remember that you will have a higher than normal cruise fuel flow, and there may also be a reduction of power to compensate for.
3) The mixture control is still where you last leaned to. OK as long as you stay at or above the altitude where you last leaned the engine, but when you descend there is a chance that your engine will become over-leaned by the increasing air density, possibly causing over-heating or engine stoppage. So, plan a higher than normal approach, such that you will still be able to make the runway even if the engine quits at any point. Applying full carburettor heat will also enrichen the mixture.
After a successful landing, you can stop the engine by turning off the mags, but remember that the engine may continue to run for a while, and there will still be fuel in the engine.
If you have a fixed pitch propeller, skip this section. If your flight manual has a recommended procedure for this emergency, follow it. The cause of this problem could be a broken cable, 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 one of three situations are likely, and can change at any time:
1) Runaway Prop (Over-speed). 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 over-speed 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 un-recoverable aft CG problem. Once you have the RPM within limits, and if you can still maintain level flight, decide whether to make for the next airport on your plan or the nearest airport. Be alert, 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 OK 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 remember you may not be able to go-around, so avoid as much as possible any need to. 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 you will need to slow down. You can by over-leaning 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 propeller logo! 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. If the pitch trim still works, make small inputs and think well ahead, since this method of pitch control is not as responsive as the yoke. If the pitch trim isn't working, you may be able to control your pitch trim with the flaps. The throttle can also be used to an extent to control pitch, but the drawback is that if this is your only method, 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, stabilised straight-in approach, with minimal manoeuvring required. Remember that the pitch change to flare is significant, so be ready for it but be careful not to over-flare. If you do, 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, 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 manoeuvring.
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 un-commanded 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. Consider each system on your aircraft and ask yourself "What would I do if this failed." These areas should be checked regularly to minimize the risk of such a thing happening. It's better to think about it while safely on the ground rather than after the failure occurs. At that point, it may be too late.