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Hand propping incident

cgoldy

Registered User
Moogerah Queensland Australia
A mate of mine was turning his prop on a rv6 with a o-320 with the maggies off and the throttle back and the mixture full lean. IT FIRED!. No chocks, inside a hangar and no one at the controls. Tuned over a few times then stopped. When he does his Maggie checks all looks fine. He repeated it for me and I was gob smacked.

How on earth could it fire if his magnetos are working as expected when the engine is running?

I don't know what type of magnetos he is running.
 
Forgot to say that the engine was cold and he stops it by pulling back the mixture.
 
How on earth could it fire if his magnetos are working as expected when the engine is running?
Know thy systems. The P leads on the mags ground out when the switch is in the off position. If a P lead has an open (break or bad connection) the mag will be hot. That is why one always does a quick mag check by turning switch to off for a quick instant before shutdown - to catch it before the condition can go on for long.

Mark J
 
I had a similar thing happen in as much as I would get a good mag check during the run-up but in fact, the P-lead was not grounding fully! I found this out because I was getting some odd readings from my newly installed EI RPM gauge. When I checked the manual for it, it clearly stated what the problem was. I made an assumption that because I was getting a good mag check, they were actually grounding out "totally" when in fact, one was not. It was the P-lead not having a good connection to the mag that caused my issue.
 
Brian,

So that sort of makes sense, but why would it not keep running when doing a mag check. ie grounding out the mags when running. ie - turning the key off! Must be something technical - mike?
 
The speed required to turn the prop on my O-320 to hand start it is alarmingly slow. Most guys who've never hand propped their Cubs probably imagine it'll be a strenuous exercise. It is not. Once you see how easily and slowly the prop can be pulled through one compression stroke and have the engine start, you'll never turn the prop casually again. It'll also reinforce that you should occasionally shut down from idle using the ignition switch(es) to assure proper P lead connection.
 
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doing a mag check during run up does check the p lead function, though maybe not the off function of the switch
 
No need to turn the engine off with mags. As Marcus said, make it a habit of doing a quick P-Lead check prior to every shutdown. With the engine at idle, momentarily switch the ignition off, then right back on. If the engine continues to run happily throughout, check your P-Leads. If the engine dies momentarily, all is well in that regard.

The mag check on run up SHOULD suggest a broken P-Lead, but frankly, the parameters we're looking for during this check might not make it stand out that well.

Or, install a Horizon digital tachometer. These tachs, in addition to being quite precise and reliable, have a warning light that shows a disabled magneto (as in one has failed) and also shows when a P-Lead has failed (ie: Hot mag). Great tachometers, and I highly recommend them.

MTV
 
If your mixture was FULL-LEAN, your carburetor is broken (if hitting the lean stops)? Happened on a 58' PA23-160 (T0-320). Fuel was still dripping into the carburetor jet some how. It was really dangerous. Carburetor was overhauled and it was safe again. You also have a broken ground on a least one magneto (the one with the impluse coupling?).

For now...Use fuel shut-off for cutting the engine (takes 3 min. at 1000RPM), and ground mags with test leads to the frame for safety.

DO NOT FLY THE with a broken carburetor AND ignition system. Both need attention. (Secure the prop with something, at least a NOTE not to turn)

(Do the p-lead check fast and below 1000 RPM [leaned out] or you may get a nasty backfire on a IO-540!)
 
Also, check the primer lines and pump if installed. I had a 0-360 not shut-down because of a leaky primer. Fuel could be getting into your induction system thru the primer?


In the tropics I in-op the primer (remove and plug at the gascolator). When it's 80F, no pre charge is needed, just a quick opening of the throttle to activate the accelerator pump.
 
The real key is never move a prop unless you are prepared for it to start. A local died recently from nudging the prop accidentally while standing in its arc. Even without impulses, these things can and will start.
 
There was a guy in Australia that destroyed 5 pipers with a flick of the prop! 1.5 milllion for that little mistake. He walked away.
 
The real key is never move a prop unless you are prepared for it to start. A local died recently from nudging the prop accidentally while standing in its arc. Even without impulses, these things can and will start.

+100 !!!!!!!!!!
 
I always pull the prop through mags off like I'm trying to start the engine, releasing the prop each time. I have always worried that there might be a load still ready to fire. Appreciate the info. Greg
 
Question?
In your first post you say...."the throttle back and the mixture full lean."
In the next post you say ...."He stops it by pulling back the mixture."
When it started, was it "full lean" or "pushed in"?
 
Question?
In your first post you say...."the throttle back and the mixture full lean."
In the next post you say ...."He stops it by pulling back the mixture."
When it started, was it "full lean" or "pushed in"?

Good catch T.J. Ahh, what really happened?
 
The real key is never move a prop unless you are prepared for it to start. A local died recently from nudging the prop accidentally while standing in its arc. Even without impulses, these things can and will start.


You are right! just a nudge or barely move a prop with the right fuel-air mixture and a hot spark and it can start. I had this happen to me. I learned the hard way. The only damage was a prop glance off my knuckle requiring one suture and me standing a few inches from a spinning propeller. I am grateful that the fellow at the controls that said "mags off" held the brakes. No one to blame but my self. Use proper technique. Or "propper technique", if you will.
 
Question?
In your first post you say...."the throttle back and the mixture full lean."
In the next post you say ...."He stops it by pulling back the mixture."
When it started, was it "full lean" or "pushed in"?

Throttle was at idle, mixture was full lean, key switch was off, engine cold. One flick of the prop and away it goes for about 3 seconds!

Then he got in and started the engine as normal. And showed me that when you turn the key to the off position ( where it was when it started unexpectidly) the engine stops as normal as you would expect.

What really happened to this experienced pilot was he had just changed the oil and wanted to pump some through before starting. But he can replicate it at will.
 
Per Lycoming -- pre-oiling is done by grounding the mags and removing the bottom sparkplugs, then cranking with the starter until 15-30 psi oil pressure. Pre-oiling is not needed or recommended during a normal oil change > 40F. If it is really cold < 32F ... preheat the oil, pour into crankcase and pre-oil, then run-up.

* It will burn out the starter if pre-oiling with full compression and/or cold oil.
* The mags will arch internal if you don't ground them with the sparkplugs disconnected.
* If you have switches (not key "off", "both", "R", "L", "Start"), just leave mags off during engine rotation.
 
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A customer of mine had his engine start in a hangar when he was pulling the prop through, it ran briefly then died. Nobody hurt, just shook up.

I was not able to duplicate the hot magneto, but I did disassemble the magneto switch and find the grease to be unusually dirty and sticky and the little silver contact points slightly discolored. It was an ACS ignition switch.

Since then when I check the magneto timing I also check the switch activation and enthusiastically wriggle the key in all positions, especially OFF to verify that it works correctly and isn't prone to accidentally being ON. I can observe the switch operation by watching the timing lights hooked to the magnetos.

Vickie
 
Also, a little tibit....

I yell clear when throwing the master switch... just in case a relay or swtich is stuck closed and/or a short to the starter.

I see many folks yelling clear only once when ready to crank after mags/mixture(s)/master in on. I think that is weak.
 
I have found several ignition switches with intermittent grounding by wriggling the key as I mentioned previously during mag timing checks. I am wondering if there is a relation between intermittent ignition switches and heavy key rings?

Vickie
 
I have found several ignition switches with intermittent grounding by wriggling the key as I mentioned previously during mag timing checks. I am wondering if there is a relation between intermittent ignition switches and heavy key rings?

Nothing beats a straight single pole toggle swtich for an item. The Cessna key thing was when they tried to make aircraft look and feel like cars (no joke).
 
There may be a few of you that know or know of Rucker Tibbs of New London, VA.

Mr. Tibbs was annualing a 180 Comanche in his hangar one winter in the late 80's (I believe). The hangar was small and the Comanche barely fit. It was up on jacks for a gear swing when Mr. Tibbs needed something from the other side of the plane. As he squeezed between the hangar door and the prop, he barely moved the prop and the engine fired once or twice. Off came Mr. Tibbs right arm at about the elbow.

Of course if you have ever met him, he will tell you it hasn't slowed him down. He's not dwelling on it, it is just "one of those things". It didn't stop his flying either. A couple years later he flew his 1939 J4 around the perimeter of the U.S. He continued maintenance work in the small hangar too.

John Scott
 
John, I met Mr. Tibbs years ago on a trip to FL. I got weathered in there. What a nice guy, he gave me his grandsons pickup to go to the motel. That place is a dragstrip on sundays, he said that pays the bills. As I remember it he made that trip around the country before he lost his arm

Tim
 
Vickie is right in checking the switch system during mag timing procedures. Toggle switches can also go bad. The last inadvertant start I had was with a toggle. The previous one was an old military style rotery switch. An AD is out on Bendix switches to check them for open grounding. The AD references the "Twist to Start" and the "Push to start" versions, however any of them can go sour. The AD references a check at idle, however I have had them backfire and mess up a muffler. Prefer to check them with a timing light. The problem with the switches are they are usually intermittent in not doing their job. I always treat the engine as "HOT". The only time I feel safe is when the plug wires are out. The rule at this shop is as soon as possible, the plug wires are pulled, and last thing back in, are the plug wires. The ACS switch also has an AD to clean the contacts every 1000 hrs. The lube in the switch can act as a carrier for the small grindings to trail across and mess up the switch. Heavy key loads on the switch does wear the workings out as Vickie is wondering.

Steve
 
Well guess I am going to stop turning the prop four of five times by hand before climbing in to start the engine. I always do a mag check before taking off but you guys got me scared now. Thanks for the story's you might of saved a few of us from some serious health problems.


Bill
 
as Vickie and Steve's Steve say, check mag switch is capable of shutting them off...

My version was a broke Plead on one of our 185's, with me between prop and hanger door when it poped over for a bit 20+ years ago.... that was scary!!! checked mag switch off, mixture lean before moving prop....
 
Also, I'm in the habit of leaving wheels chocked, even in the hangar, until ready to push out. Then if I NEED to move the prop, treat it as "loaded and ready to fire". This electricity stuff is evil, even if it's just a "theory".

Thanks. Cubscout
 
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