Originally Posted by PT6driver (Post 2147102)

Pilatus provides a maximum TQ chart in cruise and have heard this is only a CYA move by Pilatus for liability reasons.

Originally Posted by JamesNoBrakes (Post 2147130)

So are you saying you run it above the maximum in this chart, or you want to?

Originally Posted by Yoda2 (Post 2147136)

I don't really have the time to answer your questions properly, though the airframe manufacturers info generally takes precedence. An engine manufacturer might state certain capabilities and limitations of an engine, though all might not be prudent to utilize regarding a particular application. Also keep in mind "that" airplane, especially an NG, pretty much records everything...

Originally Posted by PT6driver (Post 2147102)

It's my understanding that this engine was derated from 1,600SHP to 1,200SHP (5 minute limitation) and then to 1,000SHP continuous.

How was this derating achieved? ITT limit? TQ limit? Both?

I ask because some of my coworkers run the engine well below it's maximum continuous ITT limit for climbs and cruise and I just don't understand the justification behind it other than, "we only have one so we'll take it easy" and, "this is the way "everyone" else runs it."

In the Series 9, Max. Continuous ITT is 760*C. We run it at 720*C.
In the NG, Max. Continuous is 820*C. We run it at 780*C.

It's also my understanding that Pratt & Whitney says you don't need to observe any specific TQ values in cruise so long as you stay under the Max. Continuous ITT. Pilatus provides a maximum TQ chart in cruise and have heard this is only a CYA move by Pilatus for liability reasons. I run the engine exactly as I've been taught but I just don't understand the "why" aspect of it all.

Why are we being taught to be easy on an engine that is already derated? I don't do well with "just run it this way." I need to understand the reasoning behind it.

Originally Posted by PT6driver (Post 2147177)

Neither.

Is there going to be unnecessary damage incurred if the engine is run up just below its max continuous ITT?

Originally Posted by PT6driver (Post 2147177)

Where did this lower ITT setting stem from? If you're a PC12 driver, do you just use the max continuous charts provided to set cruise power?

Originally Posted by bozobigtop (Post 2147224)

I was always taught to use a cruise power setting on the PT-6 engines, that would be somewhere at the top of the green range for your engine. The only time I ever used Max Continuous is in a simulator while training usually during emergencies such as windshear, icing, and falling out of the sky. I have well over 9000 hours flying airframes with PT-6 engines. As a A&P/IA Max Continuous means you have an emergency and it means just what it says and is not necessarily limited if you need the power.

Originally Posted by JohnBurke (Post 2147256)

All damage is unnecessary. You are not going to incur damage by operating within limitations. You will not achieve the maximum life from the engine, however, and in turbine engines, a small reduction in ITT/EGT can provide a substantial increase in service life and or a significant reduction in wear. Heat in the turbine is the enemy.

When I run a PT6A-67, I run it at the max continuous EGT as long as I need it there, which is during the extended climb, because that's what the engine is rated to do for that period of time. Derating is irrelevant.

Derating the engine allows the engine to be operated at it's maximum rated shaft horsepower to higher altitudes, rather than running into limitations early on and having a torque or temp curve to respect.

I don't operate a PC-12, but I do operate the -67 quite a bit. The max continuous ITT for our operation is 800, which I'll use until in cruise, and reduce to whatever value is needed to run at the top of the green/bottom of the yellow. It's typically in the 750 range, torque in the 3000 ft/lb range. I'll generally leave the prop at max 1700 if I'm heavy, and wont' retard it until I'm empty in cruise, then back to 1,500. We're derated substantially. I run up against torque limits at lower elevations, temp limits at higher elevations, as one does with a turboprop.

I don't have limitations other than max for the aircraft I'm flying, but in any aircraft, I observe the most restrictive of the engine or airframe manufacturer limitations.

Originally Posted by PT6driver (Post 2147534)

I'm assuming you're in a multi.

Originally Posted by JohnBurke (Post 2147751)

Don't assume. You'd be wrong.

Again, if you have limitations prescribed by your particular airframe, follow them.

The PT6 has a variety of limitations that are applicable, and they vary not only with the dash number of the engine, but also with the propeller and airframe installation.