ICO versus Mag Switch
Joined: Jan 2001
Posts: 418
Likes: 1
From: In "BIG SKY".
Hi Guys,
A lot of inexperience has been taught here, none if which is really wrong, but also obviously not understood by some.
The Gipsy, Cirrus engines were all stopped by switching off the mag' switches and advancing the throttle. The opening of the throttle was to lean the mixture beyond the running stage. The Tiger Moth/Magister etc. did have a mixture control when built, 'studefather', but a lot have had the lever removed. The lever only selected Rich or Weak mixture, never a cut off position. The Chipmunk did, in later years, get a cut off toggle that cut the fuel.
When stopping one of these engines should either of the mags' be "hot' the engine will continue to run and you switch off the fuel and wait 3-4 minutes for the carburetor bowl to drain. Then call the engineer to fix the problem as the engine is still capable of firing.
One thing that has been missed here is the long standing Airworthiness Directive for the Bendix magneto switch that the majority of GA aircraft have fitted. The AD calls for the engineer/mechanic to do a "Dead Mag check" at inspection time, by switching the magnetos to OFF briefly, with the throttle at idle to make sure that the switch does indeed ground the magnetos. This is what you are checking at each "Dead Mag" check.
There are plenty of manuals and information out there that call for the mag' switch to be set to off momentarity, with the throttle at idle at every shut down. This is nothing new. The Left Right routine is OK as far as it goes but it does not check the actual switch, which is why it is called for.
On my own aircraft, which has a dead mag' check at every shut down before the mixture is pulled to cut-off, I had it start 2 days later when the starter was activated for a check. It only fired three times, but the guy standing nearby changed his shorts!!
They are always live!! Remember that, and you will retire with most of your essential components intact.
Speedbird48
A lot of inexperience has been taught here, none if which is really wrong, but also obviously not understood by some.
The Gipsy, Cirrus engines were all stopped by switching off the mag' switches and advancing the throttle. The opening of the throttle was to lean the mixture beyond the running stage. The Tiger Moth/Magister etc. did have a mixture control when built, 'studefather', but a lot have had the lever removed. The lever only selected Rich or Weak mixture, never a cut off position. The Chipmunk did, in later years, get a cut off toggle that cut the fuel.
When stopping one of these engines should either of the mags' be "hot' the engine will continue to run and you switch off the fuel and wait 3-4 minutes for the carburetor bowl to drain. Then call the engineer to fix the problem as the engine is still capable of firing.
One thing that has been missed here is the long standing Airworthiness Directive for the Bendix magneto switch that the majority of GA aircraft have fitted. The AD calls for the engineer/mechanic to do a "Dead Mag check" at inspection time, by switching the magnetos to OFF briefly, with the throttle at idle to make sure that the switch does indeed ground the magnetos. This is what you are checking at each "Dead Mag" check.
There are plenty of manuals and information out there that call for the mag' switch to be set to off momentarity, with the throttle at idle at every shut down. This is nothing new. The Left Right routine is OK as far as it goes but it does not check the actual switch, which is why it is called for.
On my own aircraft, which has a dead mag' check at every shut down before the mixture is pulled to cut-off, I had it start 2 days later when the starter was activated for a check. It only fired three times, but the guy standing nearby changed his shorts!!
They are always live!! Remember that, and you will retire with most of your essential components intact.
Speedbird48
