One of the best things about attending the 3-day engine managment course run by the GAMI folks is that you get on a list where they answer questions sent in by participants and also talk about the latest things they have discovered. What is great about these folks, is that they work on measured data, nut supposition or "old pilot tales."  They were the guys who discovered with data that running an engine 50 degrees ROP, for example, is usually about the worste place you can set it.  There have been discussions about "turbo cool-down" on this board and although I don't fly a turbo, I thought you who do might find this interesting. The author flies a turbo-normalized Bonanza.

Grads,
We have a "White Paper" on the concept of post-flight turbo cooldown by a former Mooney test pilot in the back of the later versions of the  APS Manual.  I've also covered the subject previously in #133.Here's another data point for you, quoted with permission.  We love data!
We instrumented a pair of thermocouples on the front turbo of our P Skymaster last night. (Isn't it a shame when you have too much time on your hands) On takeoff we saw the exhaust side of the turbo case go up to 1100 degrees F, cooled down to around 750 in cruise, on approach with 15" manifold it dropped to about 700. On taxi back to the hangar it had reached 845, during a 5 minute "cool down" we were back to almost 1000. We did not calibrate the thermocouples, so there could be a large error in the actual temperatures recorded, but the relative relationship holds. Based on Walter's comments and this rather simplistic test, I'm changing the shutdown procedure.  Jack Wybenga <wybenga@excite.com>
So c'mon, quit abusing that turbo!  If you're really worried, chop the mixture in the flare, roll to a stop, and call for a tow.  The tower and other traffic will get really excited, but your turbo will love you!
(I'm joking, gang, I'm joking!)
Best...
John Deakin

What they said in the course was that for the great, great majority of turbos, the rea; cooling is done of final approach.  The temps increase during taxi, and the temps really increase during idle.  Perhaps Commanders are different?  Seems unlikely, but possible.  Interested in what Robin,Sven and others say.

Scott Sedam
N4843W, '77 114
Willow Run (YIP)
SE Michigan