Everyone seems to be scared stiff of what they perceive is "shock cooling". There are all sorts of fancy power settings that various pilots are taught (perpetuation of aviation myths) for the descent including the one inch MP per 1000 ft of descent and variations thereof. People are even apprehensive of reducing power in the circuit beyond a certain figure.
It is sometimes difficult to sort out fact from myth when it comes to engine handling on aircraft such as the Chieftain/Navajo genre.
There is some interesting reading in
www.avweb.com by some pretty experienced engineers. Navigate your way to Pelican's Perch which are articles by a well respected pilot called John Deakin. He has recently written a damning article on the ATSB accident report on the Whyalla accident.
These are a few selected extracts from Avweb articles on shock cooling.
From Kas Thomas - aeronautical engineer who wrote in March 1966 issue of TBO Advisor: "Shock cooling - Myth or Reality". His article examined the physics and metallurgy of shock cooling and concluded that, contrary to the conventional wisdom, it is not a major contributor to cylinder head cracking"
He added that there is no scientic proof that cooling plays a significant role in cylinder damage in aviation. He says that to his knowledge that Bob Hoover has not experienced any problem with cylinder-head cracking on his Shrike, despite his rather odd predisposition to feather bothengines while in a redline dive.
Kas Thomas continues: Every pilot flies through rain occasionally and rain should make a very effective coolant) more so than mere air, certainly) - yet no one ascribes cylinder damage to flying through too much rain. If shock cooling were a definate hazard your engine should fall apart when you bring the mixture into idle ciut-off at the end of a flight. CHT's fall off at a rate of 100 degrees F per minute or more in the first few seconds of shutdown - triple the rate that starts the typical "shock cooling" annunciator blinking. The why are we worried about pulling the throttle back?
There are many opinions on engine handling for Chieftains and Navajos. Everyone from LAME's to pilots have favourite set- in- stone theories which they swear will save engine wear and tear. Most of them are just that - theories and not established measured facts.
I suggest that you research the engine manufacturer's websites and trawl through the various first class articles on engine handling in Avweb and the Lycoming Flyer magazine.