Piston shutdown procedures

[flyingron]

That way you know the mags are cold before you go pushing around the plane by the prop with a warm engine

You no NOTHING of the sort. All you know is that the OFF switch temporarily worked when you switched through it. The cheap-ass key switches commonly used will often wear to the point where they can appear to be off and the key removed but they'll unground at least one of the mags. You could do all the hot mag checks on my old switch you wanted and it would still be hot half the time. The mechanic learned that the hard way when she was timing the mags and managed to discharge the cap through her hand.

 

[Dan Thomas]

About once a year or so I will flip the mags to off on a plane I am running or just flew and nothing will happen, the engine will keep on running. I've seen p-leads fall off, break, or just have too much resistance to function, as well as failed ignition switches or failed wires in the magneto. Magneto p-leads fail "safe" most of the time in that a failed lead will not shut down the engine. Safe in flight is quite unsafe on the ground when the prop stops vertical and you need to hook up the tow bar to push the plane back. The engine doesn't even have to start, just kick over to kill you. Another reason to always treat the prop like it could turn at any time, just like gun safety 101, "a gun is always loaded"


2 seconds of time could save a life. Show me a pilot who has/will never turn a prop by hand for any reason and I will show you a liar.

I too have seen broken P-leads enough to know that they do fail. Vibration does it, especially if the leads aren't properly supported or given enough slack between the firewall supports and mags. Even then they don't last forever. Hot mags have killed more than one unwary pilot, and the uninitiated seem to just have to turn that propeller, too.

Some Bendix mag switches have an AD against them for faulty grounding. I bet there are lots of them out there that haven't been checked and replaced.

http://rgl.faa.gov/Regulatory_and_G...C14960A415D956BD86256E520053A53E?OpenDocument

The ACS mag switches also have an AD-mandated 2000-hour check of the internal contacts, for starter operation rather than mags, and they often get overlooked, too. They need cleaning and lubricating, and obviously if the old lube gets hard and dirty, as it will, it could affect mag grounding as well.

http://rgl.faa.gov/Regulatory_and_G...B8ABD56539B4684886256A3E00759DBF?OpenDocument

Incidentally, that ACS AD applies to brand-new switches sold even today, too.

How many of you mechanics are aware of these ADs?

Dan

 

[N801BH]

.....Incidentally, that ACS AD applies to brand-new switches sold even today, too.

How many of you mechanics are aware of these ADs?

Dan

Don't be silly.... ALL mechanics are up to speed on ALL AD's and are smarter then the rest of us.......

Tom D will be along shortly to strengthen my theory..

 

[Henning]

You no NOTHING of the sort. All you know is that the OFF switch temporarily worked when you switched through it. The cheap-ass key switches commonly used will often wear to the point where they can appear to be off and the key removed but they'll unground at least one of the mags. You could do all the hot mag checks on my old switch you wanted and it would still be hot half the time. The mechanic learned that the hard way when she was timing the mags and managed to discharge the cap through her hand.

Real planes don't have keys.... If you have a play plane, take your hand off the key for a moment.

 

[airheadpenguin]

Jaybird, I believe the idea is to detect a hot (malfunctioning) mag. If the p-lead does not ground properly then the mag will not shut down. At all. So if the engine *doesn't* stumble when you bring the mags offline then something is wrong.

I just check this with a left/right/both check at 1k RPM before shutdown

 

[Skylane81E]

Dan, I am, but cannot speak to others

 

[Fearless Tower]

How many of you mechanics are aware of these ADs?

Bigger question is how many pilots are aware of it....it is not necessarily the kind of AD that gets checked once a year at annual and it can be performed by a PPL.

 

[21541803]

Using Henning's technique, flicking the ignition to off and back on again, followed by pulling the mixture to starve the engine;
some advise to switch the ignition back on to only one mag, say the Right one (closest to the off position on the switch) instead of both. What will be the reason for this? Less of a shudder/"engine fit" on shut down?

 

[Skylane81E]

So every time you turn the prop you have a qualified pilot at the controls?

 

[Skylane81E]

Nope,
But I also don't have the engine primed, mixture rich, key on and throttle cracked when I pull the prop around to attach the tow bar.

Just pokin at you:wink2:

 

[PilotAlan]

Just me, but since i have to manipulate the area around the prop to push it back in the hangar, I do this:

Aggressive lean on taxi (to prevent fouling, since my hangar is at 5500 feet)
Taxi to the hangar
Advance throttle to ~1500rpm
Mixture to idle cutoff

The idea is to use engine/prop momentum to carry the engine through several rotations with the mixture shut off, making sure there's not a fuel/air charge partly compressed and ready to pop.

 

[Chip Sylverne]

Just me, but since i have to manipulate the area around the prop to push it back in the hangar, I do this:

Aggressive lean on taxi (to prevent fouling, since my hangar is at 5500 feet)
Taxi to the hangar
Advance throttle to ~1500rpm
Mixture to idle cutoff

The idea is to use engine/prop momentum to carry the engine through several rotations with the mixture shut off, making sure there's not a fuel/air charge partly compressed and ready to pop.

I do this as well, then say out loud "mags and master off" to prevent having to turn around halfway home 'cuz I can't remember if I turned off the master.

An old timer told me he pulls on the carb heat for thirty seconds or so before he pulls the mixture. Said it would prevent any "kickback". I dunno, sounds like an owt to me. I'd just as soon not introduce unfiltered air if it's not necessary.

Anyone else heard of his?

 

[Henning]

I do this as well, then say out loud "mags and master off" to prevent having to turn around halfway home 'cuz I can't remember if I turned off the master.

An old timer told me he pulls on the carb heat for thirty seconds or so before he pulls the mixture. Said it would prevent any "kickback". I dunno, sounds like an owt to me. I'd just as soon not introduce unfiltered air if it's not necessary.

Anyone else heard of his?

Don't see it working myself.

 

[Skylane81E]

Do what now?

Having a CAT gauge on my plane I can tell you that it is hooey, heat full on it doesn't get scorchingly hot, I think what he is after is to evaporate all the fuel away, but those vapors are what burn.

 

[EdFred]

I do this as well, then say out loud "mags and master off" to prevent having to turn around halfway home 'cuz I can't remember if I turned off the master.

Leave the beacon on. If you leave the master on, the light keeps flashing/rotating.

 

[Skylane81E]

Leave the beacon on. If you leave the master on, the light keeps flashing/rotating.

I do that, then as I am walking back to the plane after lunch I see the flashing and get to start my prayers a little sooner. Nearly two hours in the restaurant and it still started,

Behold the power of talking to the plane, begging it to be good to you, "oh I'm sorry baby I'll never do it again, just start, please, oh please, I'll wax you when we get home!"

 

[tonycondon]

I just pull the mixture to idle cut off and then everything with an on/off switch goes off. I think it was Dave Bahnson who figured that about 2/3 of people into prop incidents involved a plane that was just sitting still idling. So i try to avoid that.

 

[Silvaire]

Leave the beacon on. If you leave the master on, the light keeps flashing/rotating.

Right and even if you're still too dumb to notice it someone else will tell you as you're walking away "Hey, you left your master on" :wink2: