Page 22 - October 2022

ASK THE EXPERT
Feathering’s Effect on ITT
by Tom Clements
When conducting the run-up propeller feathering check, have you noticed what happens to ITT? Of course, most of our attention is directed to the propeller tachometers, as it should be, making sure they decrease rapidly and significantly. Some pilots conduct the check just as they were taught in the Seneca or Travel Air or Duchess they used for their multiengine training: Making sure they observe the rapid onset of RPM decrease but then pushing the propeller levers fully forward before the speed drops so far as to labor the engine. Others, realizing that the propeller is not mechanically connected to the compressor in the “free turbine” PT6, go ahead and allow the speed to stabilize as the propellers go to their largest blade angle. This speed will almost always be below 500 RPM, even if the condition levers were set for High Idle.
A clever and common procedure is to conduct the PT6 feathering check while taxiing down a long taxiway on your way to the run-up pad or takeoff runway. With the propellers in feather, forward thrust is eliminated and it is very quiet for the passengers. Remember that it’s a no-no to have the power levers over the Idle gate into Beta while the propellers are feathered, so make certain they are at Idle first, then pull both prop levers fully back
20 • KING AIR MAGAZINE
into feather. You will feel an initial acceleration surge as the blades take a more positive bite of air followed by no thrust at all as they become feathered. It’s quiet, taxi speed is nicely controlled, and the brakes can be spared any usage.
Although the propellers feather rapidly, the reverse is not true. They typically require 20 seconds or more
OCTOBER 2022