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looking for help from some experienced Caravan pilots.

So for the 208B Caravan we have our emergency checklist, which for engine failure tells us to power idle prop feather and fuel lever to idle and basically do a forced landing, For flameout tells us to either turn ignition on if Ng>50 or put the fuel lever at shutoff and try an airstart, For FCU malfunction tells us to go power idle and use emergency power lever.

But, how do I know which one of those caused my engine to start quitting? Don’t all those just result in the torque falling to idle and engine basically quitting? How do I know which checklist to run?

Thanks for the answers.

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I don't have a lot of Caravan time, but I had that same question in training and the way it was explained made sense. It's best to consider engine failures, roll-backs, and flameouts, as well as your response, in practical scenario-based contexts to ensure the best diagnosis of the cause based on your flight regime as well as the indications.

For example:

SCENARIO 1: You just flew through heavy precipitation, or maybe hit turbulence at high AOA that interrupted airflow and caused a compressor stall. If your engine subsequently rolls back, you ought to be thinking flameout first, and should try to catch it quick before Ng decays below 50%. So, Power to idle to slow fuel flow, and get the ignition switch on right away! (Give yourself a shot at a quick relight without the inflight checklist.) If you miss that and the engine seems to be running all the way down, secure the fuel condition lever some time below 50% Ng, and if you have time after setting your glide speed and looking for a landing site, be prepared to try an airstart.

SCENARIO 2: If the engine just rolls back to idle for no apparent reason you ought to suspect the FCU and engage the EPL (after power to idle...) to regain control. It may be that you misdiagnosed #1, so in reality one procedure could blend into another.

SCENARIO 3: This is the mechanical engine failure. You should really only go straight to this one if it is fairly obvious that it isn't # 1 or 2, because something a bit more dramatic happened. (I.e. there's no good reason to suspect a mere flameout due to heavy rain or maneuvering, and RPM didn't stop at idle with other conditions indicating normal.) Something bad has probably happened - maybe there was a loud bang indicating a hard internal failure of some sort, vibration, oil streaking from the cowling, or you just sucked a 25 lb goose down the intake. You don't want to risk a fire or further damage by leaving it running or attempting a relight if something major has broken, so set your speed to best glide and just shut it down (IDLE, FEATHER, CUT-OFF) then look for a place to land.

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    $\begingroup$ Good answer, thanks! $\endgroup$
    – leha007
    Feb 21 at 1:49
  • $\begingroup$ Weren't you driving Caravans right after you retired from the military or something? Did you ever try to actually run the engine off the emer lever as a demo or anything? I've never heard of that on any other PT-6 powered a/c but the Caravan and Pilatus. $\endgroup$
    – John K
    Feb 21 at 5:45
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    $\begingroup$ @JohnK, I actually took about 13 years off flying, then just did it part time for a few years until Covid hit. I’d like to get back to it. I've never used the actual EPL - In the Navy we did a few practice approaches using it in the T-34 simulator. Too much risk of toasting an engine to practice in the airplane, it was pretty touchy as you mention. $\endgroup$
    – Michael Hall
    Feb 21 at 18:11
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    $\begingroup$ I once met the test pilot on the world's second jet airliner, the Avro Canada Jetliner en.wikipedia.org/wiki/Avro_Canada_C102_Jetliner, a guy named Don Rogers, when I worked at DeHavilland Canada. The Jetliner was powered with 4 Rolls Royce Derwents, which had typical early fuel controllers (RR had cancelled the engine program for the original engine, and Avro was forced to go with 4 off the shelf Derwents instead of 2 of the newer one - this is 1948). Like managing a team of very finicky and flighty horses, he said. $\endgroup$
    – John K
    Feb 21 at 18:43
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With a flameout, the engine stops completely, having flamed out. Torque goes to zero, temps fall off toward ambient.

FCU failures in the PT-6 result in the engine keeping running, but the torque rolls back toward a flight idle baseline, because one of the pneumatic sensing circuits in the FCU malfunctioned and the regulating circuits go off-line, with only the idle circuit in operation.

For the Caravan and PC-12, being a single engine airplane, they added the emergency power lever to mitigate the risk of a single FCU failure putting you into the ground. It turns the engine into a 1940s type of turbine engine, where the fuel controller was very crude, and fuel flow was controlled directly by the pilot (the emer lever is basically a garden hose faucet - your eyes and brain become the fuel control unit).

You now become like a WW2 ME-262 pilot managing his delicate and finicky Jumo turbojets, having to very carefully observe temperatures and torque as you make adjustments, and having to be very gentle with power changes to avoid overtemping or flaming out. But at least you are still flying.

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  • $\begingroup$ Thank you John. Ok, so Ill identify FCU failure by my power dropping to idle. How would I distinguish between flameout and engine failure for example? Because for flameout Id like to try to restart it using the airstart checklist. For failure, we wouldn’t want to try to restart a failed engine? $\endgroup$
    – leha007
    Feb 20 at 22:34
  • $\begingroup$ I'm not a Caravan driver but I know the PT-6. As I said, it'll still be running, just at idle. If it flames out, torque and ITT will go to zero, oil press lights will come on, all that stuff. For FCU failure, you implement the emer lever and run the engine with that. The Caravan has an EMER LEVER caution light. I'm not sure if that comes on to indicate FCU fail, or to indicate status when you;ve selected it to run the engine with. Don't you have a Caravan flight manual? $\endgroup$
    – John K
    Feb 20 at 23:00

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