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into the world is the measurement of the resistance needed to bring the temperature reading into line. That measurement, stated in degrees of temperature drop (they call it “ITT trim”), is stamped on the engine’s data plate and the corresponding temp stick is installed.
In the future, if the temp stick fails on that engine, the correct replacement can be ascertained by checking the engine data plate.
Temp stick 101
For the PT6 engines in most King Airs, the temp stick is located over the engine inlet (T1) and hitched up to the T5 harness. It can go by many names (trim stick, T1 probe, T5 stick) but there is only one temp stick and it is sensing the ambient inlet temperature of the engine. It takes that reading, reduces it proportionately and transfers it to the engine gauges.
Other aircraft engines have a similar feature. They call them “pilot pleasers” because somewhere along the line an engine designer thought pilots would be nervous if they knew the real temperature reading inside their engines. My understanding is various methods were developed to make the engine gauges read lower than the actual temperature while still preserving accuracy. In
simplistic terms: Your PT6 temp stick is a resistor and the electrical signal going from the engine to the cockpit goes through this stick, which has been adjusted specifically for that engine. The stick reduces the electrical signal on the way to your temp gauge. In reality it is a pretty sophisticated resistor, considering the change in OAT as you go from ground level to altitude. (FYI – if you’re a “sparky” reading this, the stick is wired in parallel, not in series.)
The most important thing for you to know is this: The required resistance of the temp stick for that engine was determined “at birth” and stamped on the data plate. The temp stick takes the engine’s real running temperature and recalculates it into what you see on your engine gauges.
Adjustable or fixed
Way back in the day, temp sticks were adjustable. There was only one type of stick. When installing a new stick on an engine, the mechanic consulted the engine data plate and adjusted the new temp stick accordingly. The stick was then sealed and installed.
Although straightforward and handy, these adjustable temp sticks were tempting to a few unscrupulous
DECEMBER 2024
KING AIR MAGAZINE • 21