Scenario Based Training is one of the things the FAA is pushing recently. Try this the next time your give someone a flight review or currency training. When the airplane is at a comfortable altitude and trimmed up for cruise flight, pull the power back about 300 RPM and tell the pilot the engine is running rough. What I would like to see happen is the pilot pitch and trim for level flight, turn towards the nearest airport and then run through fuel, mixture, carb heat, boost pump, primer. What usually happens is the pilot says "Huh" and continues on the same heading while starting to loose altitude. Then they usually start to mumble about things like "it could be carb ice" etc. I then pull back the power a little more and say "Getting worse". Most of the pilots continue to sort of stumble around until I finally pull the power to idle and tell them they have an engine failure.

I now teach primary students as well pilots in currency training to follow the same procedure for a rough running engine as an engine failure:
Pitch to maintain altitude (rather than best glide), Turn towards the nearest airport (rather than an emergency landing area), run the engine failure checklist. If they have not fixed the rough engine by running the engine failure checklist call ATC or Flight Service and give them the same information they would for an engine failure, What is the problem, where are they, where are they going. Whether they declare an emergency or not makes no difference.

Try it an see what happens.

Thats a good idea! I'm heading out to the airport in about 30 minutes and I'll have do that with my first student (pre-private). That works great with multi-engine stuff. Too often the only "engine failures" we get/give in training are total loss of power from one engine.

Out of curiosity, are you trying to model a particular engine problem? IE, loss of power + card heat = worse? Sounds like a clogged air intake (loss of power and then warm air makes it worse without any increase).

When it happened to me it was a cam failure. One of the exhaust cam lobs just went away causing the exhaust valve to remain closed on that cylinder. The engine started running rough and kept getting rougher. I screwed around for longer than I care to admit before I started for a place to land, I also lost about 500 feet of altitude. In my case the engine never stopped running, the oil temp, oil pressure, the single cylinder head temp (not on the affected cylinder) and exhaust gas temp were all normal. As you may have guessed this is a subject near and dear to my heart!

There are lots of things that can cause an engine to run rough or quit, mag problem, improper mixture, bad fuel, carb ice, even an air filter collapsing and partially blocking the intake. There are only a few things we can do to try to fix an engine problem in the air. They are all on the engine failure checklist. If you haven't fixed your problem with that checklist your not going to fix it. Go someplace and land safely while the engine is still running and do not descend until you are over your landing area. Even at a controlled airport if you tell the tower you have an engine problem and don't want to descend until your directly over the airport he will help you get down safely. If the controller gives you a hard time declare an emergency. That is the gist of my debrief for the rough running engine exercise.

BTW, even it the pilot does everything correctly on the rough running engine exercise I usually give them an engine failure too. I'm just a SOB when it comes to emergency training.

I lost partial power once due to a stuck valve as well. Of course, it happened right at rotation on a touch and go. Go figure.

When doing the scenario described above I have people get to the airport, then make a power off approach. No sense assuming the partial power is going to continue.

On my PVT check ride on downwind heading home after the ordeal, the DE asked me to check the windsock. At that time he not only pulled the mixture full out but turned off the fuel (simple lever between the seat in a 152). Now I know why my seat was so sweaty - he had another pilot taking his checkride right before me. WHHHHEEEEEEE.

Chris - wishing I could still fit in an 152.

That is a good way to give yourself vapor lock and turn the scenario into a real emergency.

Good idea in theory, but I personally teach FITS syllabi and scenario-based doesn't always work that great.

First boldface of the emergency checklist - punch DE in the face for being a complete idiot

Vapor lock a carburetor engine at 60 kts? I doubt it.

Doesn't make it a good idea though.

When my instructor does that, he randomly does it, even at 600 feet right after takeoff; just yanked it out and asked me where i was going to land.