Pt6a-67 Series Engine – Correct Start Procedure

[3 green's]

HI ALL

Calling all PT6A boffins !

When starting a “cold” PT6A-67 series engine does one simply wait for NG to rise above 13% or do you wait for NG to stabilize at number above 13%.

Thanks

Cheers

[Elliot Moose]

That depends on what sort of a power source you are using. It is always best to get the highest N1 possible before throwing the fuel to any PT6 to make for a cooler start. If it's really cold (like -20 to -40) and you are using battery start you will likely put the fuel on as soon as you get min N1 since your battery is taking an awful pounding and you won't likely get much more anyways.

Using a good warm battery, let it get to the point where the acceleration of the N1 is slowing a bit then give her-- especially if you are going to have to cross start the other engine. This is of course not applicable to the PC12!

With a GPU let it more or less stabilize every time (but not for long as you are burning the starter motor) before adding fuel.

I've done the "extreme cold" thing with a few of the PT6 series (including the 67) and always been told to go with the highest N1 possible respecting power available. Never had any problem getting the -67 to go with a good battery. The coldest I ever did was a -113a (Caravan) with oil temp down around -40. We did make min Ng but only just!:D

['%MAC']

As Elliot Moose told you the correct way to do it, here is a way to do it if you have a weak battery; no GPU. Get N1 spinning as fast as she’ll go, 10% maybe, with one paw on the condition lever bring it up to the detent but don’t allow it to set in. The RPM will rise, but so will the ITT, just as the needle is about to bust the red line cut the fuel, the ITT will drop faster then the RPM, when the ITT is down again introduce some more fuel and repeat the process as necessary. It kinda sounds like the engine is stuttering, vroom, vroooom, vroooooom, voooshhhh. You may momentarily exceed starter duty cycle, but if you’re out in the boonies at least you’ll be able to leave. Oh, just prior to shutdown close the inertial separators, they add to the ITT problem, and closing them without gen power zaps too much juice. You may want to practice this alternate start when your boss isn’t around, but it’s of a nice to know nature when you’re stuck out in the nature. I'm assuming you're on an ought two.

[Elliot Moose]

%MAC
Aaaahh yes the old "milking" start. I've had to do that one a couple of times. Not generally recommended, but a good way out of a tight pickle. I only ever had to do that one on a BE200 because of the battery freezing on a cold day after a long inbound with little electric draw. With the battery out in the wing, and well cooled it just didn't seem happy. Strange thing was, that it was always a HOT engine that I had to do that on!:D