Ignition switch settings

Right magneto is "hot" (ungrounded). The "OFF" position grounds both
mags.

That was my understanding too, but after arguing the
point with two very experienced pilots yesterday, I
wondered how prevalent the contrary view might be.

Most pilots don't understand much about aircraft systems,
and many who have automobile maintenance experience don't understand
magnetos. They make a lot of assumptions and sometimes harbour many
misconceptions. A magneto's primary winding is grounded to kill it, so
when the key is in the R position, the L magneto is grounded, and vice
versa. Even the terminals on back of the switch are labelled R and L
and when the appropriate positions are selected, the other terminal is
grounded. Can confuse someone trying to test the switch itself unless
they know what the principles are.
Another misconception: that the magneto is somehow connected
to the aircraft's electrical system. They're afraid to turn off the
master switch in flight lest it kill the engine.

I know from personal experience that a lot of pilots continue to have
serious misconceptions about such things, but it still bothers me. This is
the sort of thing that is part of every run-up, and therefore should have
been part of the aircraft systems knowledge requirement to get the
license--not necessarily the grounding issue, but which magneto actually
fires its set of plugs.

"Peter Dohm" wrote in message
...
Right magneto is "hot" (ungrounded). The "OFF" position grounds both
mags.


I know from personal experience that a lot of pilots continue to have
serious misconceptions about such things, but it still bothers me. This
is
the sort of thing that is part of every run-up, and therefore should have
been part of the aircraft systems knowledge requirement to get the
license--not necessarily the grounding issue, but which magneto actually
fires its set of plugs.



I don't get the connection. Why would the licenced pilot need to know which
mag and which set of plugs is firing on Left or Right key position? Know why
the mag check is important and what to watch for during the mag check, yes.

On Mar 3, 5:11 pm, "Travis Marlatte"
wrote:

I don't get the connection. Why would the licenced pilot need to know which
mag and which set of plugs is firing on Left or Right key position? Know why
the mag check is important and what to watch for during the mag check, yes.

Here's one reason (and this scenario initiated the post
in the first place). My 182 failed the run-up yesterday
on the "left" mag. I knew which cylinder it was through
my JPI. But which plug? The upper plug is easy to check, but
the lower requires removal of the lower cowling, which is
a 2-person job to replace.

Right magneto is "hot" (ungrounded). The "OFF" position grounds
both
mags.


I know from personal experience that a lot of pilots continue to have
serious misconceptions about such things, but it still bothers me. This
is
the sort of thing that is part of every run-up, and therefore should
have
been part of the aircraft systems knowledge requirement to get the
license--not necessarily the grounding issue, but which magneto actually
fires its set of plugs.



I don't get the connection. Why would the licenced pilot need to know
which
mag and which set of plugs is firing on Left or Right key position? Know
why
the mag check is important and what to watch for during the mag check,
yes.


No, but he should know that that the Right mag is hot (firing plugs) and the
Left mag is cold (not firing) when the switch is in the "R" position, and
that the Right mag is cold (not firing) and the Left mag is hot (firing
plugs) when the switch is in the "L" position. That much systems knowledge
would seem usefull for a safe and reasonable Go/NoGo decision prior to
take-off, and also to explain a problem to an efficient manner.

Knowledge of the specifics of how the ignition system works could be very
usefull in the case of "stealing your oun airplane" because you lost the key
at a remote hunting/fishing spot; but I can not imagine that being part of
an accredited licensing test.

Peter

"Peter Dohm" wrote in message ...
:
: No, but he should know that that the Right mag is hot (firing plugs) and the
: Left mag is cold (not firing) when the switch is in the "R" position, and
: that the Right mag is cold (not firing) and the Left mag is hot (firing
: plugs) when the switch is in the "L" position. That much systems knowledge
: would seem usefull for a safe and reasonable Go/NoGo decision prior to
: take-off, and also to explain a problem to an efficient manner.
:
: Knowledge of the specifics of how the ignition system works could be very
: usefull in the case of "stealing your oun airplane" because you lost the key
: at a remote hunting/fishing spot; but I can not imagine that being part of
: an accredited licensing test.
:
: Peter
:
:

But they sure as heck should know that turning off the master switch will not turn off their engine.

There are some old engines that did use battery power for
the ignition and in those, the battery master must be on.
But, in general aircraft built in the post WWII period have
two independent magnetos and the battery is used for lights,
starting and radios, etc. Some aircraft had one magneto and
one coil/distributor [like a car], so the AFM/POH should be
read. Also ignition operation should be checked on the
ground as part of the pre or post-flight checklists.



"Blueskies" wrote in message
t...
|
| "Peter Dohm" wrote in message
...
| :
| : No, but he should know that that the Right mag is hot
(firing plugs) and the
| : Left mag is cold (not firing) when the switch is in the
"R" position, and
| : that the Right mag is cold (not firing) and the Left mag
is hot (firing
| : plugs) when the switch is in the "L" position. That
much systems knowledge
| : would seem usefull for a safe and reasonable Go/NoGo
decision prior to
| : take-off, and also to explain a problem to an efficient
manner.
| :
| : Knowledge of the specifics of how the ignition system
works could be very
| : usefull in the case of "stealing your oun airplane"
because you lost the key
| : at a remote hunting/fishing spot; but I can not imagine
that being part of
| : an accredited licensing test.
| :
| : Peter
| :
| :
|
| But they sure as heck should know that turning off the
master switch will not turn off their engine.
|
|

"Jim Macklin" wrote in message ...
: There are some old engines that did use battery power for
: the ignition and in those, the battery master must be on.
: But, in general aircraft built in the post WWII period have
: two independent magnetos and the battery is used for lights,
: starting and radios, etc. Some aircraft had one magneto and
: one coil/distributor [like a car], so the AFM/POH should be
: read. Also ignition operation should be checked on the
: ground as part of the pre or post-flight checklists.
:
:
:

How old are you talking, Jim? Any specifics? Engine, airframe?

On Sat, 3 Mar 2007 19:11:50 -0600, "Travis Marlatte"
wrote:

"Peter Dohm" wrote in message
.. .
Right magneto is "hot" (ungrounded). The "OFF" position grounds both
mags.


I know from personal experience that a lot of pilots continue to have
serious misconceptions about such things, but it still bothers me. This
is
the sort of thing that is part of every run-up, and therefore should have
been part of the aircraft systems knowledge requirement to get the
license--not necessarily the grounding issue, but which magneto actually
fires its set of plugs.



I don't get the connection. Why would the licenced pilot need to know which
mag and which set of plugs is firing on Left or Right key position? Know why
the mag check is important and what to watch for during the mag check, yes.

On the right (or left) looking toward the propeller, or t'other way
round? (And tractor or pusher? And are the mag designations different
on the two engines in a Cessna 337?) Maybe it's time to label mag
switches Port and Starboard, mateys!

Don

In article ,
"Travis Marlatte" wrote:

"Peter Dohm" wrote in message
...
Right magneto is "hot" (ungrounded). The "OFF" position grounds both
mags.


I know from personal experience that a lot of pilots continue to have
serious misconceptions about such things, but it still bothers me. This
is
the sort of thing that is part of every run-up, and therefore should have
been part of the aircraft systems knowledge requirement to get the
license--not necessarily the grounding issue, but which magneto actually
fires its set of plugs.



I don't get the connection. Why would the licenced pilot need to know which
mag and which set of plugs is firing on Left or Right key position? Know why
the mag check is important and what to watch for during the mag check, yes.

So you can tell which mag has the problem -- ehether it is plugs,
harness or the magneto itself. Sometimes it is just a fouled plug; other
times it is a dirty cigarette; other times it is a loose harness
connection. Learn it and use it!

"Orval Fairbairn" wrote in message
news
In article ,
"Travis Marlatte" wrote:

"Peter Dohm" wrote in message
...
Right magneto is "hot" (ungrounded). The "OFF" position grounds
both
mags.


I know from personal experience that a lot of pilots continue to have
serious misconceptions about such things, but it still bothers me.
This
is
the sort of thing that is part of every run-up, and therefore should
have
been part of the aircraft systems knowledge requirement to get the
license--not necessarily the grounding issue, but which magneto
actually
fires its set of plugs.



I don't get the connection. Why would the licenced pilot need to know
which
mag and which set of plugs is firing on Left or Right key position? Know
why
the mag check is important and what to watch for during the mag check,
yes.

So you can tell which mag has the problem -- ehether it is plugs,
harness or the magneto itself. Sometimes it is just a fouled plug; other
times it is a dirty cigarette; other times it is a loose harness
connection. Learn it and use it!


You and Peter seem pretty set on this and I don't quite understand why.
Here's two scenarios I'm thinking about:

1) I do a mag check and notice that I don't get an RPM drop on the Left (or
Right) position. So I taxi over to the garage and I say to the guy, I says,
"Say! I think I may have a broken P-lead. Do you have time to fix it while I
go get some lunch?"

2) I do a mag check and notice that the engine runs rough on the Left (or
Right) position. So I taxi over to the garage and I say to the guy, I says,
"Say! I think I may have a fouled plug that I couldn't clear with leaning.
Do you have time to fix it while I go get some lunch?"

Now, if I happened to be out on a lake somewhere and had a fouled plug that
wouldn't clear, I'd walk over to my tackle box, see, and pull out the green,
spotted jitter bug. 'Cause when I'm desperate for dinner, that's what I
always use. In the morning, I'd pull all four of the lower plugs because by
the time I translated left or right for top or bottom on the left or right
side, I'd... well, I'd rather be fishing and, chances are, it's one of the
lower plugs.

-------------------------------
Travis
Lake N3094P
PWK