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Why are King Air 350 PT6 operating temps the way they are? I’ve been taught to cruse at 785 as per Beech/Textron maintenance recommendations. My non typed not really qualified FO claims I am ruining Engine life by running these temps. He likes to cruse in the 750 range. I don’t really care so long as he doesn’t kill me.

But to say I’m destroying the engines by running at 785 is a little bit annoying.

Am I actually damaging the aircraft by operating at 785?

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    $\begingroup$ First off, why isn’t your F/O qualified or typed? Secondly, why are you listening to him if he’s not qualified in the aircraft? $\endgroup$
    – MD88Fan
    Commented Jan 10, 2022 at 0:57
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    $\begingroup$ "Ruining" is a bit of a stretch if you are following Beech/Textron recommendations. Show him that and end the conversations. However, running cooler will ALWAY result in longer life, so his argument is not without some merit... $\endgroup$ Commented Jan 10, 2022 at 2:53
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    $\begingroup$ Extraordinary claims require extraordinary evidence. Can this guy cite information, either from Beechcraft or Pratt & Whitney Aircraft of Canada confirming this? If he's not typed in the thing, I'm not buying it otherwise. $\endgroup$ Commented Jan 11, 2022 at 3:57

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Actually, you are both wrong. If you look at the BE300 cruise power tables you will see that you are supposed to set torque for power (based on P.Alt., temp. and weight) and not ITT. When you purchase a new King Air 300/350 it comes with a Pratt and Whitney 'how to care for your engine' booklet which explains why this is so. Using ITT to set power can result in premature replacement of the power turbine blades (perhaps even before the mid time hot section check is due) and/or the engine not developing its full rated power towards the end its life (which renders the performance section of the handbook useless). The engine is designed to use constant torque settings throughout its life. The resulting ITT's will slowly increase as the engine ages, but will still remain within operating limits. This will result in the engine always producing its full rated power output (which is what the performance section of the handbook is based upon). Setting ITT for power is simply a guessing game. If you set them low, then the engine is probably just fine, but you have no clue as to whether you are meeting the power requirements necessary to make the performance tables valid... which is not fine. One day (with perhaps 3,000 hours on the engines) you calculate your single engine climb out of Eagle in IMC as 500 fpm, an engine quits, you begin the single engine alternate departure procedure (which may require 400 fpm) and you only manage 300 fpm! and then it's "hello granite".

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