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How to handle a bad magneto?


VFlyer
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I won’t say the specific school, but I am flying out in the Midwest and one of our helicopters has developed a fairly bad drop (shuttering) with one of its magnetos.

 

Here is a little background:

 

If I remember correctly, the left magneto will have the typical smooth drop, while the right has a noticeable stuttering, shaking, and very audible drop (I believe below the 7% in the checklist). This, for the most part, has gone uncorrected, with people in a hurry and assuming nothing is wrong, and has developed into some uncomfortable situations while actually airborne.

 

I’m not sure of the actual cause (detonation perhaps), but I’ve heard from 3 people now, that the helicopter will start to yaw and shake violently, prompting them to want to enter an autorotation. This doesn’t sound particularly safe.

 

In my leisure reading, it seems like engines can speak to you and give you warning signals before something catastrophic happens. Needless to say, I’m unsure about flying this helicopter without anything being done, especially with critical engine happenings while in flight.

 

I’ve faced many hard drops with Cessna’s, but it is usually taken care of by increasing the RPM, leaning the mixture, and “clearing it out”. Not sure if the same theory applies to helicopters, as it's somewhat of a inconvenience in an airplane, but seems to have caused some relatively nerve racking flight conditions.

 

So my question is: what do you do about a rough running magneto? All of the CFI’s I believe are well aware of the hard drop, but yet no action has been taken.

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Write it up and get it fixed....

 

§ 91.7 Civil aircraft airworthiness.

 

No person may operate a civil aircraft unless it is in an airworthy condition.

 

The pilot in command of a civil aircraft is responsible for determining whether that aircraft is in condition for safe flight. The pilot in command shall discontinue the flight when unairworthy mechanical, electrical, or structural conditions occur.

 

§ 91.405 Maintenance required.

 

Each owner or operator of an aircraft

 

(a) .....shall between required inspections,..... have discrepancies repaired as prescribed in part 43 of this chapter....

Edited by rotormatic1
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By all means get it fixed, it will only get worse. I can't imagine a busy flight school that doesn't have a spare set of mags sitting on a shelf somewhere. A good mechanic should be able to change a mag in about an hour, depending on how many panels or cowlings he has to remove to get to it..

Even if they don't have a spare, once off the machine with the proper parts they can be overhauled

in about 3 hours. Talk to your CFI or mechanic it should be addressed.

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Leaning the mix and cleaning the plugs in airplane world pretty common however it is taboo in helicopters.

 

With that said I've done it with skids on the ground, 15 " map just like mag check setup, lean out and try again.

 

Once again though probably won't find many helicopter types that wouldn't get unnecessarily nervous over this maneuver.

 

Definitely should squawk the deficiency, that should be one of the first pre flight actions you're instructor taught you how to do.

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Thanks for the advice so far, it sounds like something that shouldn't be taken lightly.

 

Perhaps I'm overreacting, but what would everyone consider to be a bad magneto? Just going below 7%? Or are the sounds and feelings something to consider as well?

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Thanks for the advice so far, it sounds like something that shouldn't be taken lightly.

 

Perhaps I'm overreacting, but what would everyone consider to be a bad magneto? Just going below 7%? Or are the sounds and feelings something to consider as well?

You will never know when you are overreacting. Sometimes you will find out with an unpleasant surprise when you under react.

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One thing you will NEVER do is try to test the mags in flight to see which one is the dud.

 

Sudden silence when you turn off the good mag, mad scramble to get left hand back on collective to enter auto, curse yourself all the way to the ground for being an idiot. No spare hand to try a restart.

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1st I'd like to clarify that leaning to check mags on a heli is just fine if the plugs were loaded up... The no-no is doing that in flight as the helicopter doesn't have a big heavy prop on the crank to keep it spinning..

2nd. If its coughing or backfiring or dropping off excessively those are bad things (I don't know what Robinson recommends as a normal % drop) but 7% of 2560 (pretty sure the r22 is around that rpm) is @180 rpm... That is telling you something especially if it is coughing..

A lot if times it is point wear or carbon buildup on the block towers and is really saying the Mags need cleaned up or overhauled

Could be poor timing of the mags, bad lead a bad plug or a mag issue. The reality is that a drop of 180 isn't THAT bad but that's why we compare to the other mag. Also there should ABDOLUTELY not be any backfiring or coughing on one mag.. Ask the mx dept to check it and don't fly until you are satisfied or have more knowledge/understanding.

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Never said it wasn't fine ;) just said most helicopter guys about have a heart attack if you reach for the mixture knob :blink: even if sitting on the ground :o

 

OP - the big difference is in a helicopter you need to have 100% power available for takeoff, landing etc so a loss of a cylinder or a mag could be a dangerous situation for a helicopter operation. one cylinder misfiring = 1/6 of the horsepower available in a a six cylinder engine, thats a huge difference ! and the yawing and shaking you describe is not a good thing !

 

at the tour company last year we had a well seasoned pilot lose a mag with max gross at high DA he was not able to maintain altitude after the loss of magneto.

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Guest pokey

Getting to the mechanic's side, now lets see,, was it "if the drop in RPM is instant---it is usually a magneto problem,,, if it sputters and takes a little while to drop----it is usually a spark plug" or was it the other way around? Helicopters should use the Iridiam fine wire spark plugs, very expensive, but so is a wreck. Some magneto problems are minor ,, some major--don't fly if you think you have either.

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Guest pokey

The no-no is doing that in flight as the helicopter doesn't have a big heavy prop on the crank to keep it spinning..

.

 

I don't think it is the weight of the prop that keeps it spinning, it is the windmilling of the prop. Ever intentionally try to stop an airplane engine from spinning in flight?---it is not easy & that is partially the reason why some applications of propellers have a "feather" mode.

 

 

BTW apiaguy,,, i know what you meant----just tried to clarify it for ya

 

(edited to add last comment)

Edited by pokey
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From the situation described, it needs to be written up and left for maintenance to clear it. I do not know why so many pilots are hesitant to write up a maintenance issue and "ground" the aircraft. If a 7% drop is the max allowed and it went beyond that then that aircraft is not airworthy until that is corrected. A small issue can lead later to a larger one. This is not a radio giving you static, it is a magneto. Loose one and you have lost a significant amount of power for you to use. Why would a pilot take a chance on that?

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So my question is: what do you do about a rough running magneto? All of the CFI’s I believe are well aware of the hard drop, but yet no action has been taken.

 

 

Abort the flight, write "rough running magneto" on the squawk sheet, and re-schedule your lesson in another ship (provided they have more than one). The CFIs should know this!

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Thanks for the advice so far, it sounds like something that shouldn't be taken lightly.

 

Perhaps I'm overreacting, but what would everyone consider to be a bad magneto? Just going below 7%? Or are the sounds and feelings something to consider as well?

 

If 7% is the max allowable drop, then just going below that is all you need to cancell the flight and squawk it so the mechanic can take a look!

 

If those other symptoms you mentioned ocurred without the 7% drop, I would still have cancelled the flight, and written up what happened on the squawk sheet.

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The noise/shuddering and yawing is one or more dead cylinders. It's common and the fix takes 10 minutes tops and is pilot level maintenance. Step 1, pull plugs, Step 2 clean plugs, Step 3, reinstall plugs IAW maintenance manual. Your CFI's should be able to do this. If they can't they should be ashamed of themselves when they ask the mechanic to do it for them. If cleaning the plugs does not solve the problem then the aircraft should be grounded and inspected to find out what is going on as it will be a very serious problem if ignored.

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Uh, oh. A pilot has diagnosed the problem: over the internet! Your out of your mind if you think CFI's should be removing and reinstalling spark plugs in a helicopter. I don't care how simple the procedure is: when you start talking about "IAW maintenance manuals" your venturing into dangerous territory. The CFI may or may not have been properly instructed. You don't know. I also don't think a pilot should be ashamed to have a mechanic do the job they were trained for and are paid to do. The only exception would be if a mechanic came back and checked their work afterword. If I were at a flight school and saw a CFI wrenching on the helicopter, I would haul ass outta there. The most dangerous thing on the ramp is a pilot with a wrench in his hand.

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The noise/shuddering and yawing is one or more dead cylinders. It's common and the fix takes 10 minutes tops and is pilot level maintenance. Step 1, pull plugs, Step 2 clean plugs, Step 3, reinstall plugs IAW maintenance manual. Your CFI's should be able to do this. If they can't they should be ashamed of themselves when they ask the mechanic to do it for them. If cleaning the plugs does not solve the problem then the aircraft should be grounded and inspected to find out what is going on as it will be a very serious problem if ignored.

 

If you are a private owner then maybe, but we are talking about a flying school. Your CFI is likely not be allowed to do it. Most companies don't allow this, and at the very least a checkout would be required. Also I don't know many who own a calibrated torque wrench. Also, nobody should ever be ashamed to ask the mech how to do anything. I bet the mech would rather explain a 'trivial' thing like this, rather than explain to the FAA why the engine failed due to a spark plug coming loose on a machine they were supposed to maintain.

 

However, I agree that this is likely a ten minute fix -for the mech-, and there is no reason whatsoever to take off with this problem.

Edited by lelebebbel
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So just how much different is it to change out a spark plug in a chopper than in a car, because I've changed those before and never had them come loose or anything?

 

Now according to the POH, I (a pilot) am allowed to change the plugs, however, as mentioned above, my school wouldn't even let me change out a light bulb! Its probably an insurance thing?

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So just how much different is it to change out a spark plug in a chopper than in a car, because I've changed those before and never had them come loose or anything?

 

Now according to the POH, I (a pilot) am allowed to change the plugs, however, as mentioned above, my school wouldn't even let me change out a light bulb! Its probably an insurance thing?

 

Insurance, liability, "I'm holier than thou"... Who knows. It's the same way at my flight school. Students are only allowed to add oil. And truth be told, some of them I wouldn't even trust with that... Missing fairing screw? Tell the instructor who then tells the mechs. It's a bit ridiculous that even the instructors can't do anything...

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Guest pokey

So just how much different is it to change out a spark plug in a chopper than in a car, because I've changed those before and never had them come loose or anything?

 

Now according to the POH, I (a pilot) am allowed to change the plugs, however, as mentioned above, my school wouldn't even let me change out a light bulb! Its probably an insurance thing?

 

The differences are plenty between car and aircraft/helicopter spark plug replacement. Aircraft have delicate screw-on plug leads that can crack easily if over tightened, the 'cigarette' of the lead should be cleaned with MEK and then a very thin coating of dielectric grease applied during assembly. The plug itself has a copper gasket that should either be annealed B4 re-use or discarded and a new one installed. Cleaning of the plug requires de-greasing, any lead deposits 'chipped' out, and then media blasted, gap re-set and checked on a spark plug testing machine. Then upon installation a very thin coating of anti-sieze compound or spark plug lubricant applied----keeping in mind that this compound will most likely contain graphite and will short out the plug if any is allowed to get near the electrode, then there is the final installation at the correct application of torque with a recently calibrated torque wrench.

 

I would not recommend a pilot take on this task without haveing done it a few times under supervision of a mechanic, and it is not a 10 minute job,, more like 2 hours, and then there is the operational check and the logbook entry.

 

Oh, and i forgot to mention to keep track of which cylinder and position each plug came from, this is for 2 reasons, (1) any abnormality of color/oil/condition can be easily traced to the problem cylinder/lead/magneto. (2) the magneto is an AC generater and fires different polarity thru it's rotation, so to get optimum life out of the plugs, we will want to 'rotate' the plugs (reverse their polarity) every 50-100 hours or thereabouts, so that the electrodes wear evenly.

Edited by pokey
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The differences are plenty between car and aircraft/helicopter spark plug replacement. Aircraft have delicate screw-on plug leads that can crack easily if over tightened, the 'cigarette' of the lead should be cleaned with MEK and then a very thin coating of dielectric grease applied during assembly. The plug itself has a copper gasket that should either be annealed B4 re-use or discarded and a new one installed. Cleaning of the plug requires de-greasing, any lead deposits 'chipped' out, and then media blasted, gap re-set and checked on a spark plug testing machine. Then upon installation a very thin coating of anti-sieze compound or spark plug lubricant applied----keeping in mind that this compound will most likely contain graphite and will short out the plug if any is allowed to get near the electrode, then there is the final installation at the correct application of torque with a recently calibrated torque wrench.

 

I would not recommend a pilot take on this task without haveing done it a few times under supervision of a mechanic, and it is not a 10 minute job,, more like 2 hours, and then there is the operational check and the logbook entry.

 

Oh, and i forgot to mention to keep track of which cylinder and position each plug came from, this is for 2 reasons, (1) any abnormality of color/oil/condition can be easily traced to the problem cylinder/lead/magneto. (2) the magneto is an AC generater and fires different polarity thru it's rotation, so to get optimum life out of the plugs, we will want to 'rotate' the plugs (reverse their polarity) every 50-100 hours or thereabouts, so that the electrodes wear evenly.

Excellent, excellent post!

 

And, if you drop a spark plug, it is scrap, marked and disposed of!

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The differences are plenty between car and aircraft/helicopter spark plug replacement. Aircraft have delicate screw-on plug leads that can crack easily if over tightened, the 'cigarette' of the lead should be cleaned with MEK and then a very thin coating of dielectric grease applied during assembly. The plug itself has a copper gasket that should either be annealed B4 re-use or discarded and a new one installed. Cleaning of the plug requires de-greasing, any lead deposits 'chipped' out, and then media blasted, gap re-set and checked on a spark plug testing machine. Then upon installation a very thin coating of anti-sieze compound or spark plug lubricant applied----keeping in mind that this compound will most likely contain graphite and will short out the plug if any is allowed to get near the electrode, then there is the final installation at the correct application of torque with a recently calibrated torque wrench.

 

I would not recommend a pilot take on this task without haveing done it a few times under supervision of a mechanic, and it is not a 10 minute job,, more like 2 hours, and then there is the operational check and the logbook entry.

 

Oh, and i forgot to mention to keep track of which cylinder and position each plug came from, this is for 2 reasons, (1) any abnormality of color/oil/condition can be easily traced to the problem cylinder/lead/magneto. (2) the magneto is an AC generater and fires different polarity thru it's rotation, so to get optimum life out of the plugs, we will want to 'rotate' the plugs (reverse their polarity) every 50-100 hours or thereabouts, so that the electrodes wear evenly.

 

Well, see, there ya go!

 

With my car all I did was take it out of the box, gap it, and screw it in. B)

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