Alternator Check during run-up

[MichaelP]

A few years ago I went to Calgary to check out a new Diamond DA20-C1 with the Continental engine.

I was stunned when during the run up the instructor turned the alternator off and then back on again with all the avionics still switched on...

Where has this 'check' come from?
It is not specified in any aircraft POH/AFM that I have read.

Recently, we have had some students from elsewhere who have done this check!
I consider the avionics to be very valuable and I would not threaten them with the voltage spike that this procedure could produce!

The Pro checklist specifies a load check... The lights, pitot heat, and flaps can be used to load the system to see that the alternator will continue to take the load.
It does not say 'turn the alternator off'.

For most of my years flying there was no check at all other than to ensure that the ammeter showed no discharge!
You soon know if the alternator/generator is not working if you do a regular scan of the ammeter, something that should be done regularly on any flight.

I have had alternator/generator failures in the past, and no load check or switch it off and on check would have predicted the coming failure.

[200hr Wonder]

Yeah you should never subject avionics to that sort of abuse. I have in the past been asked to do a load test with Pitot Heat, Lights etc, also have done it by switching the battery off *not* the alternator.

Perhaps the instructors and students where not aware of what the check was doing. I always like to take the time to explain to my students the purpose of the check.

An alternator check is done to ensure that it is providing electricity to the aircraft systems. So we load it up to make sure it can keep up, alternatively with method a, we remove the assistance of the battery to make sure it can keep up.

Either way, I still think it is a bit silly.

[niwre]

Either way, I still think it is a bit silly.

A load check silly? Care to explain?

[Cat Driver]

I was stunned when during the run up the instructor turned the alternator off and then back on again with all the avionics still switched on...

The more I read this forum the more stunned I get with the stupidity displayed by some pilots and their ignorance of the subject they are supposed to be teaching.

[Zapp Brannigan]

Not too sure if I remember this correctly but, on a C172 isn;t the ALT switch turned off to check if the low voltage light comes on? Should this be done just after start up though, not when all the avionics are turned on. Maybe the instructor just mixed that up.

[200hr Wonder]

Either way, I still think it is a bit silly.

A load check silly? Care to explain?

Oops my bad, let me clarify, the instructor, he should have known better.

[costermonger]

Not too sure if I remember this correctly but, on a C172 isn;t the ALT switch turned off to check if the low voltage light comes on? Should this be done just after start up though, not when all the avionics are turned on. Maybe the instructor just mixed that up.

I think that's the reasoning behind that sort of check, but a quick check of a POH (172RG's all I have close at hand) states the method for checking that the alternator is functioning properly is to simply load up the electrical system during the runup and making sure the needle doesn't move more than a needle's width from it's previous indication.

Maybe the fixed gear 172's have a different procedure, but I doubt it's that different.

[Big Pratt]

I was stunned when during the run up the instructor turned the alternator off and then back on again with all the avionics still switched on...

Please tell me you're trolling.

Not too sure if I remember this correctly but, on a C172 isn;t the ALT switch turned off to check if the low voltage light comes on?

Sorry, it's been a while since I flew a cessna but wouldn't this light be on with the battery master on and before engine start? Just asking.

Also, is it me or are the puppy mills pushing 200hr wonders out the door with little to no basic system knowledge these days?

BP

[comanchepilot]

Where I was doing my training, it was common practice on the singles (DA-20's and C-172R's) to load the electrical system to ensure the alternator was working, however...

On our twins (Seminoles), the practice is to turn one alternator off and watch the other pick up the load, then restore it and do the same to the other alternator.

I had always thought this was odd for the same reasons as everyone has commented on here, but never really did get an answer on it.

Seminole POH:

"The alternator output should be approximately equal for both alternators"

This is all I see for verification of the proper operation of the alternators.

I can see in the singles, having such a minor electrical load, that one might have to "load" the system to have a charge register on the ammeter, but in the twin with all the toys we have running, there is always a bit of a draw, so this has never been necessary.

Has anyone else experienced this difference at their schools?

[Louis]

MichaelP: My impression is that someone in the "chain of instruction" pulled that procedure out of a place where the sun rarely shines upon seeing an item possibly written as "Alternator - Check" in a checklist. And it's "infected" other pilots in the vicinity.

Now, I would hope the owners/mechanics get to clarify this bit of procedure with the pilots concerned. The figures I've heard for the avionics in a Katana (or pretty much any other plane out there) should be convincing enough.

Sorry, it's been a while since I flew a cessna but wouldn't this light be on with the battery master on and before engine start? Just asking.

Yes. In addition to the ammeter that would be indicating a discharge, if only due to some lights and electrical gyros spinning up.

Goodbye,

Louis

[Single-Engine IFR]

[quote="200hr Wonder"]Yeah you should never subject avionics to that sort of abuse. I have in the past been asked to do a load test with Pitot Heat, Lights etc, also have done it by switching the battery off *not* the alternator.

Perhaps the instructors and students where not aware of what the check was doing. I always like to take the time to explain to my students the purpose of the check.

An alternator check is done to ensure that it is providing electricity to the aircraft systems. So we load it up to make sure it can keep up, alternatively with method a, we remove the assistance of the battery to make sure it can keep up.
quote]

My only reference at hand is the Cessna 172, but I don't think it's possible to turn the alternator off without turning the battery half of the switch off. You can turn the alternator off with the battery left on.

I might be wrong so I'll accept any corrections.

SEI

[ahramin]

Most Cessnas use the two part rocker switches for battery/alternator which will turn the alternator off if you turn the battery off.

For those of you in other airplanes turning the battery off with the alternator left on, consider that the battery acts like a capacitor and damps down spikes from the alternators. If you turn the battery off, any spikes from the alternators are feeding directly into your avionics.

Just follow the POH.

[Tango01]

http://www.flightdiscovery.com/download/DA20chek.pdf

Simple. Engine starts first, then the avionics master switch comes on. This is standard. You never turn on an engine with any avionics on.

At runup, you load the system with all the electrical goddies to see if it holds.

With solid state avionics these days, the avionics master is a must to have (most new airplanes com with one). Also getting a Transient Voltage Suppressor inline adds extra safety.

[Dave T]

I was taught this same technique of turning the ALT on and off. After my private at a new school the instructors made sure to put an end to anyone doing that. We just used the loading up the electrical system technique.

I honestly didn't know any better. From my first flight in a 172 that is what the instructor told me to do when I got to alternator on the checklist.

In the twin however we did do it that way. It was even said out loud. Left alternator off, right alternator has the load.

[MichaelP]

Cat Driver please give us all the proper information...

The more I read this forum the more stunned I get with the stupidity displayed by some pilots and their ignorance of the subject they are supposed to be teaching.

The reason I am stunned is that I have had to pay for two Transponder repairs due to this action, and I am concerned that people are being taught something for which there is no written requirement nor justification.
Even though I teach in school aircraft, I have owned aircraft in the past, and I treat all aircraft as if I was paying for the maintenance.

At this school the low/high voltage light is illuminated as soon as the battery master switch is turned on.
The alternator is turned on after start according to the checklist and the light is observed to go out while a charge is observed on the ammeter.
If it is working of course!

I teach the students to wait for the high initial charge to stabilise in the normal range before turning the avionics on.

My understanding is that many of the newer avionics have protection against voltage spikes in the system. But not all systems are as modern.

[C-GGGQ]

Not too sure if I remember this correctly but, on a C172 isn;t the ALT switch turned off to check if the low voltage light comes on? Should this be done just after start up though, not when all the avionics are turned on. Maybe the instructor just mixed that up.

I think that's the reasoning behind that sort of check, but a quick check of a POH (172RG's all I have close at hand) states the method for checking that the alternator is functioning properly is to simply load up the electrical system during the runup and making sure the needle doesn't move more than a needle's width from it's previous indication.

Maybe the fixed gear 172's have a different procedure, but I doubt it's that different.

With a 172 POH (circa 1979) in front of me, there is no Alternator check or load check in the POH/ Checklist. My instructor would kill me even if i did the live/dead mag check (shut off both mags and turn them back on to see if the engine actually starts to shut off) just before we shut the plane down if the avionics were on.

[Cat Driver]

MichaelP:

Where do all these stupid ideas come from?

How can these things become part of flight training without the designated test flight examiners clueing on to the fact the instructors do not know what in hell they are doing?

I would fire the instructor that turned out a student that was taught like the following:

My instructor would kill me even if i did the live/dead mag check (shut off both mags and turn them back on to see if the engine actually starts to shut off) just before we shut the plane down if the avionics were on.

There are two seperate issues here that show that a lot of instructors do not understand what they are doing.

Issue number one is turning off both mags to determine if there is a live mag.....that one drives me nuts as it is totally uncalled for and no engine likes to have its ignition turned off while running as it produces unneeded stresses on the engine when the mags are turned back on...the higher the RPM the more stress.

Issue number two is they do not understand the relationship between ignition and the charging system....what does turning the mags off and on have to do with the voltage to the radios?

So who is checking on what the DFTE's are doing?

[C-GGGQ]

I would fire the instructor that turned out a student that was taught like the following:

My instructor would kill me even if i did the live/dead mag check (shut off both mags and turn them back on to see if the engine actually starts to shut off) just before we shut the plane down if the avionics were on.

There are two seperate issues here that show that a lot of instructors do not understand what they are doing.

Issue number one is turning off both mags to determine if there is a live mag.....that one drives me nuts as it is totally uncalled for and no engine likes to have its ignition turned off while running as it produces unneeded stresses on the engine when the mags are turned back on...the higher the RPM the more stress.

well for one thing this check was always done just before you went Engine Idle cutoff so engine was at idle not high rpm, and its in the checklist for the plane. Turning off the Avionics switch before you do it is just a precaution, you have to shut it off anyway when you shut the plane down. Now to be fair, when we got the new plane (2000) it was no longer in the POH or the checklist but for the 1979 172 it was there.

[Cat Driver]

C-GGGQ:

I have watched hundreds of instructors and private pilots do the live mag check with the RPM between 1000 and 1500.

I had a Cessna 150 in my fleet when I owned a school that these idiots blew two mufflers off of doing the live mag check by turning off the mags at to high RPM and waiting for a second then " BAMB " the fu.ker goes...hell I watched the idiots do it.

Lets use some common sense here and examine the live mag issue.

In fifty five years and around thirty thousand hours of flying I do not recall any live mags showing up on the airplanes I have flown...true a lot were turbine and jet ...but the issue is really blown way out of importance because if the airplane does have a live mag it will show up on the next run up.

If you are really that paranoid about a live mag you can check it without shutting off both mags together.

TEACH YOUR STUDENTS TO NEVER EVER TURN A PROP BY HAND ON THE GROUND WITHOUT BEING AWARE THAT THERE COULD BE A LIVE MAG.

Who can say that a mag did not become live just after doing that last mag check using both mags off for the check.

God I get frustrated with the lack of airmanship in flight training and I just don't understand how there can be so many DFTE's that are so careless or ignorant that these things such as shutting off both mags to check for a live mag are still so common.

That is my rant for today.

[tiggermoth]

Let me give you an engineers perspective on this discussion.

First Cat drivers points are all correct, however I do disagree with what he says about live mag checks. When I fly my 172 or do a runup on piston aircraft at work I always do a live mag check for my own safety. I want to know when doing maintenance that when the switch is off, the mags are dead. I do NOT want the mag to fire when turning the prop during maintenance. As a further precaution I even like to turn the prop backwards whenever I can to make sure it doesn't fire. Furthermore, some airplanes (Beech Baron is one) have AD's that require a live mag check periodically do to problems with the switch. So, why not do one at the end of every flight, BUT only with the engine BELOW 1000RPM.

As far as the alternator test, the instructor who teaches to turn it on and off is going to eventually break something. This is a bad habit to get into for the day he eventually starts flying turbine aircraft, as some this test would either shear the generator shaft or even cause the engine to cook itself. (long story) The correct way to check it has already been discussed, look for ALT Fail light before start, after start, turn everything on to see if the alternator will keep up.

[Cat Driver]

Tiggermoth:

No where did I say not to do live mag checks.....my posts were to point out the logical and easiest method to do them.....if you are doing a mag check during the run up you are also checking for a live mag...if it were necessary to shut off both mags at once for the live mag check it would be taught that way in the run up mag check...

.....if when checking the mags you note a loss of power/RPM as you shut off each individual mag it has shown clearly that there was not a live mag problem present during the run up.

....if you wish to do the live mag check after the flight it can be done by checking for power loss on each individual mag..

But in the final analysis I guess it really does not matter all that much to me because I'm far, far removed from the FTU mentality....praise God, Allah, Buddah and Satan.

Like you I treat a propellor like a 357 Magnum. I never pull the trigger thinking it is not loaded.

Here is something else for all you top guns in the training industry to ponder over, some day you may be applying for a job to someone like me who looks for airmanship as one of the most important qualities in a pilot.....it does not take long for me to figure out if a pilot has airmanship or if a pilot is a robot.

Right now I am looking for pilots for a very good paying job with 1/3 of the year off....when I select pilots you better believe I look deep into their background and their knowlege of how things work.

[tiggermoth]

Sorry Cat, i guess I just read your previous post wrong. You are 100% correct with using the mag drop check to also test for live mags. I just prefer to do a live mag check at the end of my flight so that if there is a problem, (such as the mags p-lead vibrating loose during flight) I can fix it before the next time I want to fly. That way I don't have to do my runup to go flying and end up taxiing back and not getting to fly (One advantage to being an engineer, I can fix my own airplane when its broke, cheaper that way ). The other reason I do live mag checks is simply because I am an engineer and like to check everything that there is to check. Thats just my opinion though.

[Cat Driver]

That way I don't have to do my runup to go flying and end up taxiing back and not getting to fly (One advantage to being an engineer, I can fix my own airplane when its broke, cheaper that way ). The other reason I do live mag checks is simply because I am an engineer and like to check everything that there is to check. Thats just my opinion though.

Tigger...we have a lot in common as I am first a mechanic, second a pilot.....but .....if I found a live mag on my airplane I would continue with the flight as planned and get it fixed when I was finished with the flight.

Maybe we could discuss marriage problems or sexual problems that are really something worth talking about instaed of simple machines like airplanes?

The discussion is also unisex.

[MichaelP]

The whole point of this forum is for people to state their opinions.

if when checking the mags you note a loss of power/RPM as you shut off each individual mag it has shown clearly that there was not a live mag problem present during the run up.

There was a time when I would agree with this.
But it is not entirely true and depends upon the type of switch used.
The old mag switches on the Tiger Moth's Gipsy were reliable in this way... But then we stop this engine with the switches in any case... Failure of the switches meant turning the fuel off.

Then there was the rotary switch fitted to the Piper Super Cub.
You could have live mags with this switch turned off even though the RPM dropped as each mag was selected, and there was an AD or SB about this.

The Cessna 152 manual advocates turning the prop by hand while priming the engine for cold weather starts.
For this reason I teach my students how to turn a prop while treating it live.
I don't agree with the school's policy of never touching a prop... One lonely cold day, far away, our former student may have to turn the prop and I don't want it to be that student's first time.

One of our Cessna 152's would start while priming with the mags off in the cold weather. I know this because I always prime the cold engine for the first start on a cold day by hand. I don't suffer carb fires etc...
When it was warm, no problem... A live mag never showed up on this aeroplane except when I turned it for its first start in the morning.
Students who got in without turning it over by hand would never know.

I've been through another diatribe on prop swinging on another forum...

[Cat Driver]

michaelP.....yes there are as many variables as there are airplanes.

But I would suggest that the people in this training forum are all flying the same basic bug smashers..Cessna's and Pipers and these are ab-initio flight training discussions.

For this reason I teach my students how to turn a prop while treating it live.

I don't agree with the school's policy of never touching a prop... One lonely cold day, far away, our former student may have to turn the prop and I don't want it to be that student's first time

.

What school would have such a policy? How will students understand the basics if they are not taught properly?