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I am just in the process of doing a bit of study in the hope of doing my Basic Gas Turbine Endorsement in the next few months, and just wanted some feedback/comments/discussion on the major hazards associated with starting, managing and shutting down a PT6 Turbine Engine (PT6 as it is the most common used Turbine Engine on an aircraft I will touch for this endorsement).

Mainly, what I am looking at is during the start - If the EGT raises above the evil 700* mark, what is the best course of action to prevent "melting the turbine"?

During Climb/Cruise Operation - What are the most common failures, and their indications?

Maintenance/Shutdown - What are the most common methods of recording Cycles? By landing or by Start/Shutdowns?

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    $\begingroup$ This is kind of a broad question with a lot of sub-questions. Is it possible to focus it a little more? $\endgroup$
    – Tyler Durden
    Commented Jan 22, 2015 at 17:46
  • $\begingroup$ Or split to three separate questions? Also the first part is probably best answered by looking up appropriate procedure in your pilot operating handbook, flight crew operating manual or quick reference handbook you should have for the aircraft you are going to use (and we can't look it up for you because you mentioned the engine, but not the aircraft). $\endgroup$
    – Jan Hudec
    Commented Jan 22, 2015 at 22:06

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  1. You MUST NOT allow the EGT or ITT (whichever is applicable) temperature limit to be exceeded in any turbine engine. If it gets close to occurring during start on a PT-6, you need to abort the start by stopping fuel flow into the engine, then conduct the appropriate checklist for an aborted start. Unlike the Honeywell / Garrett TPE single-shaft engines, the PT-6 normally won't get close to the temperature limit on start. The Garretts I used to fly in Metroliners had to get right next to redline and stay there on every start. One reason that PT-6 engines are so much more relaxing to fly.

  2. On takeoff / climb, just don't exceed the maximum temp limit; regulate the power lever(s) to keep below it. I've never had a failure of a Pratt except for bleed air leaks.

  3. Airlines count cycles as a start, flight, and shutdown. If one of these did not occur, you did not have a cycle.

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The evil mark you are talking about varies. There ara all kinds of PT6, ranging from around 500SHP to 1700SHP, each of them with different limits, including ITT limits. Which PT6 are you talking about? Overtemperature during start means that something is wrong with the engine. Either the starter did not crank the engine fast enough, the engine hot section is worn out or something is wrong with bleed valves/FCU.

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  • $\begingroup$ "Starter did not crank the engine fast enough" might be an issue with the air source for the starter, not the engine. $\endgroup$
    – SomeoneSomewhereSupportsMonica
    Commented Apr 17, 2016 at 9:30
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Do not mix EGT and ITT. EGT is exhaust gas temperature and ITT is Inter stage temperature.

Normally when starting a PT6 you should watch ITT and depending which PT6 model you use maximum ITT may vary but it`s around 1600 degrees Fahrenheit.

I work for Pratt & Whitney and PT6 is probably the best engine ever made in it`s class as someone mentioned. When starting a PT6 the engine will not get close to the maximum allowable ITT unless you have a problem. Good engine choice hope you will have good time flying with this engine.

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  • $\begingroup$ Hello JoBlow and welcome to Aviation.SE. Would you mind to add some interpunction into your answer to make it better readable? $\endgroup$
    – DeltaLima ♦
    Commented Jun 17, 2015 at 21:23

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