PT6's, King Air's and flameouts.

[scubabri]

Ok, I think I understand the engines on the King Air pretty well, but I had a friend tell me of something that I thought I would ask here.. since you guys know everything.

He was mentioning that he was flying a C90 through a rain cloud, and the engine was flaming out and re-igniting. His ITT and torque would momentaraly drop and the engine sounded like it was shut down for about 3 seconds.

He is afraid that the engine will completely flame out and require a restart.

My argument is that it couldn't (shouldn't) happen as long as the igniters are on, otherwise, who would buy a plane that everytime you flew through heavy rain, the engine flamed out.

Am I understanding this correctly? Anyone experienced this?

B.

 

[Brother Francis]

Flameout due to water ingestion in rain is not unprecedented. It is rare, and it must be some seriously heavy rain, but it has happened. Never heard of such with a PT-6, though.

PT-6's have inertial separators for engine anti-ice. If water ingestion was truly the problem, selecting engine AI might have resolved it.

 

[scubabri]

the ice vane thing is pretty cool, but for water ingestion, I would think that the AI's would take care of it, I'm just wondering, how bad is so bad that they don't take care of it and you get a flameout.

but unfortunatly, I only have what I belive based on what I know about turbines, which is not much, but growing.

b

 

[B190Captain]

I have encountered some heavy rain and have never had that problem, even with the Engine AI off. (PT6A-67D)

 

[Torqued]

The auto ignition on the PT-6's that I'm familiar with all use a torque pressure switch to turn on the igniters. When engine torque falls below a predetermined value (about 500 Lb.) the igniters are energized. That would explain the engine loss of ITT and torque and then the relight. The cockpit auto ignition switch only arms this system and does not turn the igniters on continuously. Sounds like the system was working as advertised. I would have thought the ice vanes would have prevented the massive water injestion that could cause a flameout, IF they were deployed?

 

[canadflyau]

You are correct the auto ignition comes on when torque falls somewhere in the range of 700-750ft/lbs... Unlike the PW-118 (like what are on the Brasilia) when auto ignition is selected on, the ignitors are on continuously.

So what happened to your friend is feasible... Selecting AI ON should prevent the problem.

 

[stillaboo]

the auto ignition comes on when torque falls somewhere in the range of 700-750ft/lbs

To be specific: on the PT6A-67D, when the auto-ignition is armed, the igniters come on when torque falls below 700-750 ft/lbs, and will continue down to 350 ft/lbs, at which point the engine will autofeather if the auto-feather is armed. On whatever PT6 powers the 1900 &1900C (I think the PT6A-65B), the igniters will come on below 500-550 ft/lbs. Probably the same idea for a King Air.

"The auto-ignition system should be armed in turbulence, precipitation, and icing conditions." -Flight Safety International 1900 POH/AFM

As far as the inertial separators (the ice vanes):

"The ice vanes should be extended for all ground operations and during flight operations when visible moisture is present and the temperature is +5 degrees Celsius or below."-Flight Safety International 1900 POH/AFM

I assume all water vapor that makes it through the prop, past the 180 degree turn into the engine inlet, though 4 axial flow compressors and a centrifugal flow compressor and to the burner can (it's not easy to do, as you can see) is taken care of by the heat of compression. The air is 600-800 degrees Celsius at the 'entrance' to the burner can, a relatively warm environment for water, wouldn't you say? And, after that, it has to go extinguish the flame in the burner can with 2 igniters which are firing constantly when the tourque drops.

I've never heard of a flameout due to water ingestion, despite not having the vanes open, and now I'm pretty sure why. If Beech doesn't think the vanes need to be open to shed water, I'd think that, while opening the vanes would be helpful, it hasn't ever been necessary.

-Boo!

 

[dogg]

Remember as well from basic turbine engine theory-Ingestion of water or ice will cause a significant pressure spike in the engine and it is the pressure spike that causes the flame to go out not actually the water or the ice. Bottom line turn the ignitors to continuous and dont worry about it.........

 

[CorpJetPilot]

I agree with everyone. When I fly through rain or ice, I turn the ignitors on, deploy the ice vanes, and bump the torque a little to compensate. I've never had a problem.

 

[400A]

flameout

I had an identical problem on a PT6-28. It finally quit on its own. Was not rain though,,, it was a boost pump making metal that finally trashed the fuel controler.

Trash would pile up at the high pressure screen, then cause flame out,, when pressure reduced it would get a little more fuel and spool back up,, then flame out.

 

[FalconPilot69]

PT6-42A

The B200 that I fly, the auto ignition comes on when the torques are approximately 400#. As far as the auto ignition goes, stimuflite checklist state that the auto ignition switches are a runway item for being armed and do not get turned off until the shut down checks.

Also, whenever flight from visible moisture cannot be prevented, and temps are below +15C, your ice vanes are to be extended. Don't know if this helps or hurts the topic. By the way, the B200 that I fly is a 1982 series, and I don't know if that will matter or not either.

 

[C-12Bubba]

PT6A-41 (C-12/King Air 200)

Falcon;

Agree 100%, same numbers with the -41 in our early '80s vintage Navy King Airs...

Our procedure is sort of automatic, if you deploy the ice vanes, get the torque drop, and recover the lost torque by bumping power up to compensate (non-ITT limited), you are doing everything you can to not get a flameout.

Autoignition comes on for lineup checks, and is shut off on after landing checks. We fly around 170 for turbulent air pen. speed, same for y'all?

Good info, thanks!!!

 

[Brother Francis]

http://aviation-safety.net/database/1988/880524-0.htm

 

[stillaboo]

My understanding is this is the only time ever that a 73 or larger aircraft was dead-sticked onto anything besides a runway with no injuries or damage (the engine was damaged before the landing). Putting a 73 down on a levee, man, that is skill!

-Boo!

 

[KingAir74]

C-12Bubba and FalconPilot69,

Our SOPs and checklists are the same as yours...auto ignites are to be turned on during the before takeoff checks and not turned off until the after landing checks. Auto ignition is great insurance against flameout. The system doesn't arm anyway until the torques are below 400 ft/lbs.