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Full power run ups?


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When we are doing pre taxi run ups wouldn't it make sense to go to full power instead of just 4000 rpm and checking mags.


It just seems like we should check full power before we takeoff to insure no engine issues?



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I've vented before about the lacking FD documentation, especially for my CTSW POH.


Placard (2007 CTSW): 3000 rpm

CTSW POH: 3200

CTSW Flight Training Supplement: 4000

CTLS POH: 4000

Rotax Operator's Manual: 4000


FWIW, I've been using 4000; I figure Rotax should get the tiebreaker, and a higher RPM will more easily show rpm differences.

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Okay now for the tiebreaker with reason.


Rotax picked 4K because before digital instruments the analog gauges weren't sensitive enough and showed small enough increments on the gauge. Plus many places around the world still use analog gauges. The only thing checking a mag drop at 4K vs 3K is the size of the drop. The more rpm the higher the mag drop number.

So 4K showed up on analog gauges well and the number was easy to discern. Then comes along digital instruments that can read in the tens and can show much smaller mag drop numbers and changes. 


Now 4K really is't needed. Can you get away with a 3K mag check with digital gauges? Sure, but I would recommend something higher like 3500 to give the engine and instrument a chance to show how much the difference really is. Using a low 3K mag check may not show how much differences between the two modules as you need to see for good diagnostic check before flight. I don't see a reason any longer to use 4K because it just adds more stress to things when it's not needed. I would consider a 3K mag drop check bottom line.


So what ever rpm you choose between 3K - 4K will work. Just pay attention to the drop. The numbers for the drop vary some between instruments and engines to. A normal mag drop can be between 50-100 rpm. The difference between modules tend to be 10-30 rpm.

I have seen some mag drops up around 150, but fairly equal between sides.


If you have a 150-200 rpm difference between sides that usually indicates one spark plug,cap or wire issue and not a module.


Why does FD have different numbers in different publications. Someone wasn't paying attention.

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Here's why you don't need a full power run up to check the engine: you are going to do one a minute later on the takeoff roll. I always check to verify full engine rpm and smoothness on the takeoff roll; if that looks off at all...throttle back and investigate.


I use 3000rpm. You just need to verify the ignition modules, no need to sling stuff around with higher rpm run ups.

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I've been using 3200 as my POH says, and I don't feel I've ever had any issue picking out the magnitude of the ignition drops; I feel I can see my analog gauge within about 25 RPM, so unless something is hairline I don't see the impact (and if I'm seeing something abnormal and am pushing the limit, I need to taxi back anyway).  I do use 4000 in the Remos I teach in because that's what the POH calls for; it's a much more dynamic affair.  I prefer the lower 3200 RPM not only because of the debris issue mentioned but because I'm much less likely to wind up messing with the parking brake not being effective enough, which is a bigger problem in the Remos than in the CT.

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