Turboprop engine procedure question

[VA AV8R]

I'm looking for a more technical explanation of why it's a bad idea to move the conditions levers on a turboprop (PT-6 powered) from cutoff back to idle IMMEDIATELY after placing them in cutoff (in other words, for those times when you really didn't mean to shutdown the engines). Thanks!

 

[banned username 2]

I'm looking for a more technical explanation of why it's a bad idea to move the conditions levers on a turboprop (PT-6 powered) from cutoff back to idle IMMEDIATELY after placing them in cutoff (in other words, for those times when you really didn't mean to shutdown the engines). Thanks!

I would say because you would be re-introducing fuel into the combustion chamber with less airflow (due to the dereasing RPM of the compressor/turbines) and without a steady flame propagation... In other words, the fire is out already and now you load it up with fuel and if/when it re-lights you get quite the pyrotechnic display out the exhaust...

 

[wingnutt]

In other words, the fire is out already and now you load it up with fuel and if/when it re-lights you get quite the pyrotechnic display out the exhaust...

...or at the very least a hot start

 

[JetBlast2000]

It would be a bad idea if you were below the min Ng value in the AFM (usually around 12%). In that case you could have a hot start if you continued. Other than that it should not be a problem it you inadvertently killed the fuel flow for any reason. In our training, if you have an engine die we use the acronym FBI, for Fuel, Boost, and Ignition. This is done to try and keep the engine going if it’s possible.

 

[joelo88]

let's just say i've seen it happen in a cheyenne (pt6-135). lots of smoke but no fire. no hot start either on restart. just run the engine clearing proceedure checklist.

 

[VA AV8R]

Well I have a friend who has seen a Twin Otter operator cycle the conditions lever between cutoff and idle as a method to avoid a hot start. In other words if you see the ITT going hot, just fuel chop it and then bring the condition levers back to idle again. Sounded insane to me.

 

[Canucit]

I thought that with the garret engines, on starting them when it got hot they just shut the fuel off with the condition levers for a second and then reintroduce fuel for the start

 

[Dan CFI/CFII]

"I thought that with the garret engines, on starting them when it got hot they just shut the fuel off with the condition levers for a second and then reintroduce fuel for the start"

On the Garretts I fly, there is no "condition lever" like that. There is a power lever, and there is a speed lever.

I have, however, seen someone who meant to turn on a generator grab the fuel switch to close, and then realize it in the same instant--it acted a lot like a mag check in a piston. (I think this is pretty close to the question you were asking)

When I worked at a Raytheon (King Air/1900 facility) Service Station, we often babied the condition levers of the 1900s that hadn't run for a few months to get them going--it was easier than hooking up the GPU (boy were we lazy).

Dan

 

[NuGuy]

I'm assuming you are on the ground when this happens.

It would probably still be a bad idea if you were below the normal starter cut-off value. If your starter cuts out during a start before you get to normal cut-off, you really risk a hot-start. Throwing fuel into an engine turning below %50 with no starter or airflow (from say an in flight start) is doing the same thing, and a sure way to BBQ the engine.

I certanly wouldn't engage the starter unless the engine is at 0% unless you want to grind some metal. At our shop, any inadvertant starter disengagements or start aborts you have to wait until the N2 has been at zero for at least 20 seconds before re-enagement for clearing.

Nu

 

[Axel]

As I recall (but it's been a while) the airstart procedure in a BE-200 tells you to moderate the ITT by placing the condition lever in cutoff momentarily it the ITT approaches the limit.

 

[FN FAL]

I'm looking for a more technical explanation of why it's a bad idea to move the conditions levers on a turboprop (PT-6 powered) from cutoff back to idle IMMEDIATELY after placing them in cutoff (in other words, for those times when you really didn't mean to shutdown the engines). Thanks!

I drive a PT-6 powered airplane and we have a new mod on the quadrant...it is a spring loaded lock out lever that prevents you from placing the condition lever "accidently" in the cutoff postion. It's a pain in the butt and I think it will lead to more problems with inadvertant placement of the lever. My chief pilot was doing my checkride today and it appeared that this was the first of the fleet modifications he had physcally seen.

There is beveled lever lock, that lets you place the fuel control lever in the low idle position without doing anything, but in order to go back to the cut off position you have to slide a small lever with your thumb. We both agreed this was probably going to cause a problem during a hot start or other engine proceedure where you need to cut fuel in a hurry.

I would think they would have had the locking mechanism so that if you did the accidental shut off of the fuel condition lever thing, it would prevent you from reacting by placing it back in the low idle postion inadvertantly.

If you accidently shut the PT-6 down when you didn't mean to, you should not place the fuel condition lever back up to the low idle position...like the one poster said, you'll get a big flame out of the stack and tower will call your boss...it happened to one of our ex-pilots.

 

[falconpilot]

WHAT?!?!?! How many times do you acidentally shut down the engines???? I mean to you land and pull up to the ramp and go to shut down and then change your mind or something???? Sounds to me like you need to plan ahead a little better... I really don't mean to sound rude or anything, but this sounds really fishy.

 

[328dude]

Well I saw it in a Dornier once. Crew forgot they needed a GPU and shut down the right engine without a hookup (thus no power) and brought the CL back to feather.

Was a pretty nice show after that.

 

[wingnutt]

WHAT?!?!?! How many times do you acidentally shut down the engines???? I mean to you land and pull up to the ramp and go to shut down and then change your mind or something???? Sounds to me like you need to plan ahead a little better... I really don't mean to sound rude or anything, but this sounds really fishy.

...sounds to me like youve never flown a caravan for any length of time

the condition levers have a "gate" which is similar to a King Air gate, but made of thin sheetmetal. when enough yahoos slap the condition lever around after many moons, the gate wears down to a nice rounded corner, rather than having a nice sharp stop. then, upon landing and exiting the runway while moving the condition lever from high to low idle, it is quite easy to slip right on thru to cutoff.

...and at least fish is better than shellfish since most are actually underwater insects, related more closely to land based models than one would think

 

[FN FAL]

WHAT?!?!?! How many times do you acidentally shut down the engines???? I mean to you land and pull up to the ramp and go to shut down and then change your mind or something???? Sounds to me like you need to plan ahead a little better... I really don't mean to sound rude or anything, but this sounds really fishy.

No...it happens. The procedure is to make the turn off, clear the runway, come to a stop and perform your after landing items. Which is how I did it on my check ride today.

However, it is rumored, somewhere, somebody, somehow, does the after landing items while on the roll out. I don't do that...nobody we know does that.

But anywhoo...there you are rushing the after landing items and you go from high idle, right past the low idle detent, into the cut off position. That's embarrasing enough...it happened to me once, a long time ago. But, the part you don't want to do, is realize the mistake and shove the condition lever back up into low idle.

I know you're perfect and make every move like a ballerina ...but evidently it's happened enough with the Caravan for them to have made a fleetwide modification to the control quadrants. I don't like the idea of this lock out device, I think it is a case of using environmental design to overcome an issue that is a human behavior problem.

A better design would have been to place a small gate lever on the fuel condition lever, similar to what you find on thrust levers of jets. If you move the fuel condition lever to cut off...you would have to conciously move the gate lever up, to move the condition lever back into a position that would schedule fuel.

 

[Swede]

At AA, there was a check airman of obvious genius who wanted to see if the fire handles of an MD-80 actually worked as advertised.

Taxiing back in after a leg, the C.A. pulled the fire handle on #2. "Yup it works" as the engine rolls back. The fatal error was in deciding he needed the engine, and restoring the fuel handle to normal after the engine had spooled down significantly.

The fuel controller thus spewed plenty of raw kero into a hot combustion chamber with no airflow. The engine was totaled as the fuel torched.

Our concensus was, "Only a check airman would be this stupid."

 

[Vortilon]

I guess he maybe shoulda tried that at the gate.....pretty funny!

I remember when I was on the ERJ, one of our chief pilots was flying with a new FO and they had no APU. We used to have to cycle the run/stop switch before starting an engine....so they went to start #2 while taxiing to the runway and the new FO mistakenly grabbed the run/stop switch on the OPERATING engine. Well, sure enough once he hit the STOP part of the switch the engine quit and they were dead in the water....no engines, no apu to start, and a Chief Pilot at the helm...glad it didn't happen to me!

 

[FN FAL]

At AA, there was a check airman of obvious genius who wanted to see if the fire handles of an MD-80 actually worked as advertised.

Taxiing back in after a leg, the C.A. pulled the fire handle on #2. "Yup it works" as the engine rolls back. The fatal error was in deciding he needed the engine, and restoring the fuel handle to normal after the engine had spooled down significantly.

The fuel controller thus spewed plenty of raw kero into a hot combustion chamber with no airflow. The engine was totaled as the fuel torched.

Our concensus was, "Only a check airman would be this stupid."

Jeeze! Did this check airman get a chance to see if pulling the fire handle past the detent and turning it, actually made the fire bottle discharge?

I know when I was younger, I was subject to inquisitive impulses like that, but you'd think a real live "grown up" would know better. It's one thing to smoke check your mom's stereo trying to make a robot at age 13, but them airplane engines are little pricey for that kind of experimentation!

I think most people who possess a curious nature about mechanical things, which would probably include pilots as whole, probably have a side to their brain that thrives on trying to stain stainless steel. The trick is to get past that phase in life on things that wont kill you, wont get you fired, or cost more money than than an intercontinental widebody captain grosses over three years to fix.

 

[skiddriver]

As I recall (but it's been a while) the airstart procedure in a BE-200 tells you to moderate the ITT by placing the condition lever in cutoff momentarily it the ITT approaches the limit.

I've done that in a BE200, and also in several helos that used PT-6 engines. I wouldn't try it during an inadvertant shutdown however, as the igniters wouldn't be firing.

I did learn not to scold my copilot to harshly one day however, when he shut down the second engine in our AH-1W on board ship without asking the tower's permission (he was in the back seat). When I pointed out that he had screwed up, he promptly rolled the throttle back to idle. The fireball hit the vertical fin of the aircraft and we had to scope the engine for damage. Luckily I got the throttle back down quickly and had him motor the engine to cool it off, so it didn't really get too hot. Not that I could tell from the guage because the ITT sensors don't read accurately the airflow is disturbed in the engine.