Engine run ups and magneto checks
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I have often wondered it we have to do our engine run ups and magneto checks right before takeoff Most ga aircraft checklist call for this check just before take off. What is the reason. If there is plenty of space, why not do the check in the chocks before taxi to find out you have a problem before getting all the way to the runway. 
8 Replies
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Ronald,
Please remain on these treads! Your feedback is always excellent!!
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Your information was really helpful. Thanks
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1147 Posts
James Holdeman:
Cold weather can take 10-15 minutes of 1,000 rpm running to see 100 degrees. 

You can speed up the warm-up by using a higher RPM than 1000 within the Lycoming/Continental-recommended warm-up range of 1000-1200 RPM.

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You want to do your runup when you have proper oil temps, and a relatively overall uniform heat soak of the engine allowing for all the dissimilar metal engine parts to come to their designed operating specifications including size. Air-cooled engines are designed with very loose tolerances to take account of dimensional changes as various metals expand and contract. As others have shared, designated runup area help mitigate debris-blasting other airplanes and buildings while performing mag and prop checks. One must have oil warm enough for a constant speed prop to activate the governor properly, too. I don't perform my runup unless I have at least 100 degree oil temps. Other than the hottest days, it takes a few minutes to get to 100....about the time it takes to reach our local runup areas. Cold weather can take 10-15 minutes of 1,000 rpm running to see 100 degrees. So, when I apply take off power, generally I have 120-130 degrees of oil temp.  
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I understand that no one should do runups in areas other than ones safe for the run up. My question is not about the area for performing but the check itself. 
Does it require and engine to be warmed up? This is a magneto check right? The questions is does the check just need to be done just before take off or can it be done sometime after start?
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1147 Posts
Richard Lafford:
You can also detect a fouled plug during the initial part of the takeoff roll by watching your engine monitor for all EGTs to rise together on initial throttle application. You do have an engine monitor don't you. ;-). For those who don't believe in such things, a $3k engine monitor just might save you a $30k engine or maybe your life someday, quite a positive cost benefit.

While I'm a strong proponent of engine monitors, I don't like the idea of trying to check EGT's after brake release -- it could be a distraction from maintaining directional control.  You can get around this by lining up, holding the brakes, and running up to your run-up RPM and checking the EGT's (along with MP, RPM, fuel flow/pressure, temps, etc.) before releasing brakes.  That only takes a few seconds -- not long enough to bother tower.  The downside of delaying your check is that if you DO find a fouled plug, you have to taxi clear, do the de-fouling run, and then rejoin the queue for takeoff.