Primarily for general aviation discussion, but other aviation topics are also welcome.
By JSAG
#1809854
During this Lockdown 2 re reading 'Be A Better Pilot' by Alan Bramson', in a section on power checks and specifically mag checks, this got my attention.
"You are not looking for an RPM drop at this stage (although many pilots mistakenly do) but if a magneto is not working there is little point in taxiing out"

He seems to be implying that you're really only checking there's no mag dead cut.

My training was no mag drop - no fly.
By Boxkite
#1809858
He's talking about the first mag check, not the power check. Like Bramson said, no point in warming the engine up or any other procedures if it fails the first check.
By JSAG
#1809864
Thanks for making this clearer.
So is he implying that if I get no mag drop at start up but no cut , proceed to power checks where still no mag drop will mean no fly?
And is likely it will recover at power checks?
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By alexbrett2
#1809865
It is useful to notice something more than just "the engine didn't stop" (i.e. that in theory both magnetos are working), as if e.g. a grounding lead has come off and so you aren't actually turning off one of them, noticing it at this stage will save you the hassle of taxiing out and finding out at the power checks. What you don't really care about is if the mag drop amounts are a bit different at this stage...

That being said, depending on the engine / aircraft, the mag drop / noise change at the power level you do the initial check at may be very hard to distinguish
By As I CFIT
#1809879
JSAG wrote:So is he implying that if I get no mag drop at start up but no cut , proceed to power checks where still no mag drop will mean no fly?


No, he's implying that there's no point in even worrying about any sort of mag drop if half of your ignition system isn't working at all. If a magneto is completely dead upon start up and you don't perform the check that he advocates, you wouldn't realise that your plane is u/s until the run-up. The point is, why wait that long to see if there's a major no-go problem when you could find this out immediately after starting the engine by doing a two-second check?

Bathman wrote:I can't see any requirement for such a check in my PA28-161 POH


It's a point of using your time wisely and being pro-active. POHs aren't there to cover items of good sense.
By Bathman
#1809880
FlarePath wrote:Section 4.4 "Ground Check"?


Which I think is what we would call power checks.

But I can see no requirement in the POH to do a mag check straight after engine start.

And looking at the C150 POH that I have to hand there’s no requirement to do a mag check straight after start there either. Only as part of the power checks.
By As I CFIT
#1809883
Bathman wrote:But I can see no requirement in the POH to do a mag check straight after engine start.

And looking at the C150 POH that I have to hand there’s no requirement to do a mag check straight after start there either. Only as part of the power checks.


With respect, I think that you're missing the point. It's not in the POH because you can't sue Cessna for wasting your time, which is all that you'd be doing by not performing the check if you do indeed have a dead mag upon start-up.

It's such a quick and easy thing to do and it could save you fifteen minutes straight off the bat. Why there's any resistance to doing it, I have no idea.
By UV
#1809885
Bathman wrote:
FlarePath wrote:Section 4.4 "Ground Check"?


But I can see no requirement in the POH to do a mag check straight after engine start.


There are other irregularities in that check list. For example it doesn’t mention getting strapped in until “Before Takeoff” checks. So do you taxi without being strapped in?

It also doesn't mention a vacuum check until what you call “Power Checks” or an instrument check until Before Take off. As you know in this country we do all that as we taxi.

It’s called Airmanship.
By Boxkite
#1809890
JSAG wrote:Thanks for making this clearer.
So is he implying that if I get no mag drop at start up but no cut , proceed to power checks where still no mag drop will mean no fly?
And is likely it will recover at power checks?

With respect, you seem to be guessing at why you are fl icking those switches. (ha ha, fl icking without the space gets donked!)
You need to remind yourself what is going on behind those switches; what the mags are doing, and what the switches are doing when you switch off the mags.
Run through in your mind the logic of what the situation could be after you have started the engine:
1. The engine may have started happily on one mag and you haven't noticed yet (let's ignore the fact for now that one or more of the plugs could be playing up), for one of these reasons (there could be others):
a) One mag is not functioning.
b) A 'P' lead has shorted to the airframe.
c) A switch has failed permanently to the 'Off' condition (irrespective of whether you can move it or not).
2. The engine has started on two mags, but one mag (or both) is permanently on (and probably was before you started the engine, making it dangerous to have moved the propeller):
a) A 'P' lead has broken.
b) A mag switch is permanently open circuit (irrespective of whether you can move it or not).

Now run through in your head what you would expect (and why) to happen when you operate each switch in ALL the scenarios above. An early mag check should identify the existence of a problem (but not necessary the cause) before continuing with everything else.
Last edited by Boxkite on Fri Nov 20, 2020 2:03 pm, edited 5 times in total.
By Nick
#1809891
It's also a good check to do at idle, prior to shutting down. If you notice a problem you can then rectify it at your leisure prior to you next outing.

Nick
By A4 Pacific
#1809893
I can't see any requirement for such a check in my PA28-161 POH


My Piper PA28 Check List says:

AFTER START

6. Magnetos........... Check for dead cut.
By Boxkite
#1809894
Nick wrote:It's also a good check to do at idle, prior to shutting down. If you notice a problem you can then rectify it at your leisure prior to you next outing.

Nick

Not to mention you could be walking away from, or handling, an aircraft with a live propeller.
Nick, T6Harvard liked this