PA28-181 Archer III Magnetos Question....

[karl neumann]

Hi...

Well i´m a CFII in an Academy here in Colombia, and the academy just to buy some almost new Archer III, with the Aspen EFD 1000 pro and another amazing stuff.

We use the Archer II for more than 20 years for training, and we are in the transition to the Archer III, and found some "deep" differences: for example, we don't understand why the Engine Start technic guide to start with just one Magneto (Left Magneto)????... and another one is about the caution in the Warm Up about the time: "Warm-Up the engine at 800-1200 RPM's for not more than 2 minutes in warm weather...."?????

Thanks!

[NuName]

I think that you might get more information on the Private flying or Instructors forums than here.

[Mark 1]

I don't know about that specific model, but key switches will normally ground the right magneto and only use the left mag when starting. The reason is that the impulse coupling is usually only on the left mag, so there is a small risk of a weak advanced spark from the non-impulse mag causing a backfire.

[slatch]

Only one mag (left) has an impulse coupler, which retards the spark for starting. If you activate both mags during starting, the non-coupled mag will fire ahead of the coupled mag, and you have a good chance of a kickback which can trash the gear teeth on the starter and the ring gear. Planes with a unified start/mag switch (key) have internal circuitry which grounds out the non-coupled mag when you turn the key to START. Planes with separate mag and start switches should be started with only the coupled mag activated; the other mag is activated after the engine starts. However, there are some aircraft with separate starter switches and Mag switches that do have circuits that ground the right mag while the starter switch is engaged. When in doubt starting on the left Mag only will help your starter live longer.

[Miles Magister]

Slatch has posted a good answer.

I would like to add a little. If you ever get rough running in flight with this magneto set up it is most commonly, but not always, a faulty left impulse magneto.

So when doing routine magneto checks always check the right one first by selecting from both - right - both - left - both. If this is ingrained to the thought process on routine checks if a pilot ever has to do it in flight then the right is normally most likely to be the good one and it will assist in the rough running drills should they ever be needed.

MM