Hi!
I just want to know what would happen if it the engine were stopped using the magnetos? During my last few lessons the key has been getting a little bit stuck when switching the magneto's off, during the engine tests, meaning that the engine almost stops. I know that this is not good, just want to know why? One of the instructors even suggested not doing the magneto tests any more...

Thanks!
Rob.

The magnetos are the heart of the engine. When ever you have any problem with the key/switch or a drop below safe rpm during runup on either mag or the engine does not stop firing immediately when the mag is switched to "off" have it fixed like NOW. A sticking switch that does not fully ground both mags could allow the engine to come alive if anyone were to swing the prop during preflight etc. Don't fool around with a bad mag/switch nor ever fly if you cannot check both mags during runup.

Norm, Commercial, instrment, multi-engine, seaplane and gliders.

The magnetos themselves have always been fine. Its just when doing the run up check, sometimes the switch get stuck in the 'off' position for a second nearly turning off the engine. I'm trying to find out why in particular its bad for the engine to be stopped using the mags.

If you accidentally turn off the engine durng a run-up using the mags, and get the mags back on before it quits, a backfire can happen. It's definitely no reason to not be checking the mags before flight though - you have my permission to reach over and slap your instructor for making that suggestion.

And if it quits altogether?

Sounds to me like the magneto switch is "FLAT WORN OUT"... This subject is right up my alley, as I own and operate a aircraft maintenance business. First off, you should not be flying an airplane with a defective switch, (Instructors Fault) but mostly the maintenance departments fault. This should be caught during a 100 hr or Annual inspection. There are two airworthiness directives on ignition switches, depending on what brand of switch it is. There is either a Bendix switch or a ACS Gerdes switch which both have AD notes. By any chance is it possible to remove the key in any position other than OFF? I would not fly this airplane for safety reasons. As Flyfalcons noted, when you backfire and engine during a run up/ magneto check it possible to damage the exhaust system. As far as your instructor not doing magneto test,,,, find yourself a different instructor. Lastly, stopping the engine using the ignition switch is not the safest practice. There are some airplanes out there that this is the only to stop the engine, but now days the mixture is pulled to stop the engine thus starving the fuel system.
-Tom

You should turn off an airplane by fully leaning out the mixture. Yes you can turn off the engine by turning off the magneto instead of leaning out the mixture. However the carb will be ready to go, fuel will stay in the manifold, and thus if the switch is bad could start accidental. This would make the error of operating the aircraft with a bad ignition switch doubly bad. If the carb and manifold are full of fuel, the engine at the right point, and the ignition switch bad, then it could conceivably start with just a gust of wind to move the prop a few millimeters.

BTW do new aircraft still use those lousy Slick and Bendix point driven mags?

Hi, some engines still do but the really new modern ones use the FADEC system. Norm

I assume thats solid state? The old Bendix/Slick's were adapted from tractor magneto's, but in the late 80's and early 90's when I was flying it was beyond me why auto ignition systems had solid state systems but airplanes had points. I have had bad magnetos several times, once during the air, fortunately not both at one time.

The FADEC system was designed by two retired Pratt & Whitney engineers in a small shop near Hartford CT that they adapted from the NorthStar auto engine. Their design and in fact their whole company was purchased by Continental Engines and the system is now available on some of the Continetals. The Liberty two place composite trainer has one of these engines and a lot of the new aircraft also have them installed. If you want more info punch into Google and type in FADEC ignition systems. Norm

FADEC Part II, Forgot to mention that the first FADEC type system was pioneered by Porsche Mooney from a basic Porsche style flat 6 auto engine and installed in a a Mooney airframe and sold as a Porsche Mooney. A similar system by Bosche was installed on the 2000 cc VW flat 4 aircooled engines that were in the 1980 to 1982 VW Vanagons. I have a 1981 Vanagon with one of these engines and it is a gem. Norm

I guess being "old school" I am not completely sold on the electronic ignition. The good thing about magneto's is they will keep the engine running until fuel exhaustion, unlike electronic that depends on battery power. A properly maintained magneto will usually not go bad. Things break occasionally, that is where proper pilot training comes into play...
-Tom

FADEC engines are outstanding,. All is super redundant and they start immediately, no mixture control is needed and in fact the only control is a throttle all else is automatic. I have flown about five of them and they are great. I have never had a mag problem in the air and I have over 4,000 hours of flying all types of aircraft from Warbirds to ultralights. Norm

progress is great

Personally, I wish the engine technology itself would improve. Lycoming and Continental have not improved in that department in a lotta years. If the powers to be would look at the induction system, for example, fuel economy, horsepower and torque could be increased so much that I think it would benefit everyone. (Except Big Oil). A while back there was an exhaust system developed that I couldn't believe the numbers on... Increase in everything except fuel consumption, at a cost of about $2500. If you really want to see how inefficient an airplane engine is, get a JPI analyzer and download the info and have a look. Continental engines are the worse as far as efficiency is concerned, but they do make a lot of power, if you have the $$.

Hi again!
Thanks for all the answers. However I still haven't found an answer I'm looking for. My worry is that someday when cutting the manetos during the engine run up, the key will get jammed a little in the off position and the engine will stop. I want to know because I'm doing a lot of solo Nav flights now, and if it does happen accidently, I want to understand what happens to the engine, what to do and what to look out for. I've been told that it can be bad for the engine but haven't been really been told why. If its just as Sport_Pilot said, then surely its just a case of starting it straight up again?

Other than that the switch and the mags have been always been fine. The switch works fine when testing the left and right magnetos and the mags themselves have never been an issue. I was in a piper Archer that had a magneto failure straight after take off, I don't no how the pilot caught it but he did and continued to a bog standard landing.

I think I understand what you are asking, It sounds like the switch or the key is badly worn. The only time that the magneto's are checked is when you are on the ground, why be worried if the failure is on the ground? If the key does jam in the OFF position during a magneto check, simply let the engine come to a complete stop then restart after the key jamming problem is solved. (This will prevent engine and exhaust system damage) When the key is in the OFF position, the ignition switch grounds the magneto's. This prevents the magneto's from providing spark. When you check the magneto's, Left and Right on the switch grounds either the left or right magneto. This tells you that both magneto's are operational. Hopefully I am not insulting your intelligence but I do not know what you know about the ignition system. As I said before, YOU should notify the maintenance department and have them replace the switch. This only takes about an hour or less to replace and the piece of mind is priceless. As a student, you should not have to worry about this as you have enough on your plate just flying and navigating.
-Tom

I am talking about solid state electronic magnetoes as used in racing cars and some industrial engines. Not battery powered. In fact electronic magnetoes are use in almost every lawn mower. Now lawnmowers never need points rarely need plugs and are more reliable than aircraft engines. I see the aviation industry continues to make outdated unsafe products.

So you want yourself or one of your buddies to be chopped up by a runaway aircraft engine?! Buddy if you have a bad ignition switch and start turning off the engine by turning off the engine, its not a possibility that someone will get killed or lose a limb, its only a matter of time! This was a very common occurance in the past!

Do the right thing! Ground that aircraft till the ignition switch is replaced and go through the normal checklist proceedure to turn off that engine. This is a result of age old trail and error safety proceedures that was only found after much loss of life and (literally) limb.

Why? Because worn ignition switch's are known to start on the ground, then completly fail in the air, or on the ground when someone it turning the prop, thats why! Once it starts to hang up, its only a matter of time till it fails completly.

Hey Sport Pilot... Based on the last three post you made I have to comment. You stated that the aviation industry continues to make outdated and unsafe products, I beg to differ. I have been in the maintenance field in aviation for more than 30 years and somewhat agree that product technology is outdated but... is not unsafe. I do know first hand that if an airplane or related system is PROPERLY maintained failure is unlikely.
Your comment about magneto switches, which is what this thread is based on, we all agree on. I have never heard of, read about, or seen an ignition switch fail in the air. (Magneto's occasionally do, but it is rare) As I said in my post #6, there are preventative measures in place, aka, AD notes that address this issue and when performed properly at the stated interval are usually a non issue. I have replaced several bad ignition switches due to bad key/lock mechanisms, never due to an electrical anomaly. Aircraft ignition switches merely provide a ground path for the magneto's.
As a safety check I do for every inspection, whether or not it is required by an Airworthiness Directive, is with the engine idling, switch the ignition off to assure the engine quits. I have seen a number of broken grounds at the magneto that without this check makes for a dangerous situation. This is commonly referred to as a HOT MAG.
-Tom

I only had about 400 hours flying before I quit. In that time I owned a plane that had 3 magnetos defective or replaced 1 failed in the air. Half a dozen stuck valves, 1 in the air. Had to replace two cylinders one which only had a few hundred hours on it. I knew of one injured. One my flight instructor who was injured when he had an engine go out during instruction, fortunately it was just a sprained foot. Another was killed in his banner tow. A few people I knew had close calles in IFR flight. I myself had a couple minor close calls due to bad weather. Another friend damaged an airplane in a hard landing due to poor piloting and heavy crosswind.

Sometime during early instrument training I found out through Aviation Consumer that the only thing more dangerous than flying IFR was skydiving. I think mountain climbing was safer and motorcycles safer than that. I quit IFR training right away, and flying altogether a year or so after that.

Now compare this, I had nothing but touble with maintenance when I owned an airplane, but since the only major problem I have had with a car was a transmission that went out, but it continued to run. I had a Caravan that never had its plugs replaced, just cleaned and gaped, and I sold it at 130,000+ miles. I have a lawn mower which I use about an hour and a half a week for 25 years, replace the plug only twice, never an ignition problem, no points to replace, and never has been overhauled. OK so now it burns oil and the choke won't completly close, so its hard to start cold, but IMO its built one hell of a lot better than any non turbine aircraft.

Point well taken, Think of this though. I maintain roughly 45 or so airplanes through my business, out of those 45 airplanes maybe two are flown on a regular basis. The others are used primarily for recreation and hours flown are few and far between. The biggest problem (excluding fuel prices) are that most airplanes are not flown on a regular basis. If airplanes were flown as often as your Caravan was driven, maintenance problems would be drastically reduced. I have a customer that fly's around 50 hours a month and he has very few problems. Folks always ask me why I do not own an airplane, Simple I know better. These are expensive to own and operate and your average person has a hard time affording one. Maintenance, Hangar rent, Insurance and on and on and on... Sorry to hear about your woes with airplane ownership, I deal with this everyday as there are many mechanics out there out to screw folks. You should see some of the sorry stuff that comes through my shop that was either just repaired or freshly out of inspection. I could go on and on. If there were not regulations to mandate inspections and maintenance, there would be a lot more airplanes falling out of the sky everyday...
-Tom

I put well over 100 hours on my airplane, but about half of my woes were in aircraft rentals. And those friends of mine were in varied aircraft and condition. When they start making airplanes that wont burst in flames and burn all occupants inside, when the wing tip crunch's into a building while taxing, then I may get back into full scale. That problem was with fuel lines pulled apart in the cockpit and it may now be solved. That and when my kids are through college.

Man, you have some really whacked ideas about flying. Your comment on airplanes burning when hitting a building is kinda scary itself. Please don't come in here saying the things you are. Flying is only as safe as the guy working on the plane. IFR flying is only as safe as the guy flying the plane and the instrumentation he is using. I am a fairly high time ATP and I have spent a lot of time in the clouds. I take offence to a very low time student coming in with the notions you have said. Don't bring it here!



Robert, to answer your question, many have answered it but not exactly what you are looking for. Turning the engine off with the key will not hurt the engine. It will however leave fuel in it and if the switch is bad, like yours sounds, it could cause someone to get hurt if they flip the prop and it fires. Your instructor is wrong to tell you not to test them, and the maint company is hanging themselves out a long way by not replacing a cheap switch. I would have it fixed before I flew it again.

Good luck.

I agree totally with the safety aspects. An airplane is only as good as the operator and maintenance folks. IFR is absolutely safe as long as you are current. There are a lots of pilots that have the endorsement and would likely have big problems if they got into the soup. (especially at night with a little rain mixed in)
I think Post #16 says the same thing as you did...
-Tom