Page 22 - May24

ASK THE EXPERT
Why Feather at Shutdown?
by Tom Clements
It’s going to do it anyway, right? Since the feathering springs and blade counterweights are always trying to move the propeller blades to high pitch – and the extreme of high pitch is the feathered position – and propeller oil pressure is what prevents the springs and counterweights from succeeding in their job, then as the (PT6) engine stops turning and hence oil pressure is lost the blades must feather. Right? So why does the checklist tell us to feather them ourselves?
There is a one-word answer to this question: Safety. Let me explain.
The engine’s oil system serves four functions. First, as in all engines, it provides vital lubrication and cooling for all of the engine’s moving parts. Second, it is used
20 • KING AIR MAGAZINE
in measuring the torque being supplied to the output (propeller) shaft so that the amount of torque may be displayed in the cockpit. Third, it is used to heat the fuel, to decrease the likelihood of liquid water that may be suspended in the fuel from turning into ice crystals
MAY 2024