Proper way to turn off the engine?

[Pe11e]

Didnt foudn this in the manual, and I'm not a real pilot so I must ask this - what is the proper way to turn off the engine? Is is via magnetos, mixture or fuel cutoff? I'm turning off the engine with mixture control, leaning it completely, means it will cutoff the fuel. This way the engine always fouls a second or two just before turning off. Is that normal? I've tried once to turn it off via magnetos, but it fouled much, so I guessed it is the better way with mixture.

Am I doing it wrong or...? Maybe my engine fouled just before turning it off because it wasn't leaned correctly?

[DHenriques_]

Didnt foudn this in the manual, and I'm not a real pilot so I must ask this - what is the proper way to turn off the engine? Is is via magnetos, mixture or fuel cutoff? I'm turning off the engine with mixture control, leaning it completely, means it will cutoff the fuel. This way the engine always fouls a second or two just before turning off. Is that normal? I've tried once to turn it off via magnetos, but it fouled much, so I guessed it is the better way with mixture.

Am I doing it wrong or...? Maybe my engine fouled just before turning it off because it wasn't leaned correctly?

After parking, let the engine run at a low RPM but not all the way at idle for a few moments to stabilize the internal engine temps, then go to ICO with the mixture. This is normal procedure for most aircraft UNLESS otherwise specified in a POH for a specific airplane.
Dudley Henriques

[JetSet321]

From the checklist our flight school uses:

Engine Shutdown:
• Throttle 1000 RPM
• Avionics/Electrical Equip. OFF
• Mixture CUTOFF
• Master/Alternator Switch OFF
• Ignition Switch OFF

[Pe11e]

Thanks guys!

[n421nj]

When the circuit breakers are modeled will surges also be modeled? So if you routinely start and stop engine with avionics on it can fry them?

[Scott - A2A]

I'm really not sure in the real world what damage would be caused, especially since in the Comanche there is no avionics switch, so if you shutdown according to the book, all Comanche owners are exposing all their electronics as if the avionics switch is on while the motor winds down.

What I do, however, is just after I pull the mixture, at the first sign of the engine winding down, I switch the masters off before the RPM drops too far. In fact, I've carried this procedure over to all airplanes in the event there is something still alive in the circuit that may be affected even with the avionics switch off.

But like I said, I'm not sure we would be modeling something that may just be theory or, something that is extra-ordinarily rare to happen. In any event, it's best to follow the manufacturer's recommendations regardless.

Scott.

[GrahamP]

Surely you would only be exposing the avionics equipment to damage if the equipment itself (i.e. radios, GPS, etc.) was also switched on in addition to the avionics master being on?

[Ian P]

All the Cessna and Piper POHs that I've seen have always insisted that the radios - or avionics master if fitted (very few C152s have them!) - are switched off before the engine is shut down. I've never heard of a radio being fried by starting up or particularly shutting down the engine, but I'm far from the most experienced to comment on that. I just do what the book says to!

We also shut down the avionics (using the master switch) on the Maule, but because I wasn't actually qualifying to fly solo on that and they were effectively pleasure flights with a bit of training on top, I never specifically read FC's POH.

Cheers,

Ian P.

[Pe11e]

Hmmmmmmm... I turned off the engine properly with the mixture, but it fouled so much and long, it was wrong completely.

- kept the RPM at 1000 for 10-20 seconds
- turned off the avionics
- pull the mixture completely (cutoff)

It fouled much more than when I turn it off my way (with magnetos).

[Ian P]

Fouling occurs when you run at low RPM with a rich mixture, so that implies you aren't leaning the mixture while taxying or idling the engine, rather than the actual method of shutting down the engine.

Are you leaning on the ground and, if so, how much?

Cheers,

Ian P.

[Pe11e]

I've never leaned on the ground (before takeoff) because I was thinking about full mixture for takeoff. Also eninge never fouled when idling with full (rich) mixture, so I thought it is a proper procedure. When I shutting down the engine my mixture is on full rich, so probably the fouling occurs after cutoff because of that?

[Ian P]

Try pulling your mixture back, quite hard, when you are taxying or running the engine close to idle - yes, you need to apply full mixture for takeoff, but just as a comparison, try leaving it full rich and taxying around for a while then shutting down, vice leaning significantly and doing the same thing.

One of the Cessnas I used to fly suffered horribly from fouling on the 2nd magneto... No idea why, but you'd get a 150/200rpm drop on it at power checks if you didn't lean during taxi. We cleared it, when it happened, by leaning a lot and applying full power for a minute with the brakes held on, but that's bad practice to do regularly as well. Leaning it to about 75%-66% while taxying, it didn't happen. It did force you to run the checklist properly during the pre-takeoff checks, though, because you could hear when someone forgot to put the red knob fully forward before opening the throttle... Cough... Cough... Ah, there's the power!

Cheers,

Ian P.

[renaissanceman]

Hmmmmmmm... I turned off the engine properly with the mixture, but it fouled so much and long, it was wrong completely.

- kept the RPM at 1000 for 10-20 seconds
- turned off the avionics
- pull the mixture completely (cutoff)

It fouled much more than when I turn it off my way (with magnetos).

Hi Pe11e,

Pardon me if I am wrong, but it seems that when you say fouling you are talking about how, when the mixture is pulled to cutoff, the engine sputters and coughs for a while before it stops. What Ian P. is talking about is actual sparkplug fouling that shows up when doing a mag check or in the maintenance hangar.

Jim

[Ian P]

Valid point, Jim.

If that is what you are talking about, Pe11e, then it is perfectly normal and don't worry about it.

Again, speaking from experience with SAC's C172SP, that spluttered and coughed its way round for a few seconds after you pulled the mixture to cutoff, while it pulled all the fuel out of the system. The club instructor who checked me out on it used to sit there and tell it to 'shut up already', then said 'thank you' when it did actually stop. One of the more experienced pilots around here can probably tell you whether the shut down time with a fuel injected engine is longer than with a carburetted engine, but I suspect it probably is, personally. I stand prepared to be corrected, though.

Cheers,

Ian P.

[Oracle427]

Carburated engines in my experience take more time to quit than fuel injected models. They also require a little more patience when leaning the mixture in flight. If you rush and lean too fast the engine may actually begin to cough and stumble a second or two after you lean too far. In a fuel injected model I find that the response is instantaneous.

When shutting down, most carb equipped aircraft run fine for a second or two after fully pulling out the mixture knob, where I find that fuel injected models instantly begin to stumble as you pull the knob out.