PC-12 Deice Boots

Michael95U

Michael95U

Well-Known Member
One of the PC-12's I manage is having some major deice boot issues. The cycle fails on the tail (1 and 3 min cycles). But it only seems to fail when we enter icing conditions. We flew it 2 hours after the last 100 hour in sunny skies and ran the boots on both cycles the entire time and had no issues. Any ideas from PC-12 drivers/mechanics? We replaced one of the horizontal stab boots at the 100 hour due to the patches leaking. The boots are all in good condition.

Thanks!

Michael
 
Had this issue in a Conquest. Came from there being water somewhere in the air lines or in the valve that would freeze and restrict airflow to the boots.

Alex.
 
Not a mechanic nor an A&P, but I would think that it is due to low airpressure for some reason to the boot itself. Once you build a layer of ice it becomes harder to inflate and the lower pressure isn't enought to blow them. Could be a restriction, loose fitting, etc...

Again, no A&P but I did stay at a Holiday Inn last night!
 
I had problems with the wing boots in an NG once. Apparently it was a bad/frozen valve in the ECS. But in my case we also lost the environmetals for the cockpit and the pressurization.
 
Michael95U said:
It inflates when in severe clear. Does not seem to work when actually in icing and only at the tail.
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I'm not familiar with the PC-12. Do the boots rely on engine bleed air or do they have a separate vaccum pump on an accessory drive?
 
Could it be that when flying in icing conditions, that the engine is operating with the inertial separator in bypass and it's "stealing" some of the bleed from the boots? Like I said, I don't know anything about the the PT-6 installation in the PC-12, but it was just a though I had. I'm probably wrong.
 
CK said:
Had this issue in a Conquest. Came from there being water somewhere in the air lines or in the valve that would freeze and restrict airflow to the boots.

Alex.
Click to expand...

I have seen the same thing several times in the Brasilia. If I recall correctly, there are sequence valves that direct the bleed air into the various boots. (The boots inflate at different times. Outboard, mid wing, inboard then tail. ) For whatever reason, on occasion, moisture can get in there and while up in the cold air and ice it can cause the valve(s) to stick and fail. I don't think the fix was huge, once the water is out of the system things work ok again.

Maybe it is something similar. . .or not. Good luck.
 
Definitely requires some more knowledge of how the system works. The various moisture/temperature theories all sound plausible, especially since you did have a leaky boot that could have let a bunch of water into the system. What indication do you have of boot inflation on the PC-12? Is there a pressure gauge, or just a light? If you take it up in cold weather (but sunny) or wet weather (but not freezing), does it fail? Or only during the combination of cold AND wet conditions? Where are the deice valves located? On the Chieftan they are under the floor so water and corrosion can be a problem (they're at the low point of the boot system so anything that leaks in through holes in the boots collects there) but it's also fairly warm if the cabin heater is running so I don't think freezing valves are much of an issue. That may well not be the case for the Pilatus.
 
Roger said:
Definitely requires some more knowledge of how the system works. The various moisture/temperature theories all sound plausible, especially since you did have a leaky boot that could have let a bunch of water into the system. What indication do you have of boot inflation on the PC-12? Is there a pressure gauge, or just a light? If you take it up in cold weather (but sunny) or wet weather (but not freezing), does it fail? Or only during the combination of cold AND wet conditions? Where are the deice valves located? On the Chieftan they are under the floor so water and corrosion can be a problem (they're at the low point of the boot system so anything that leaks in through holes in the boots collects there) but it's also fairly warm if the cabin heater is running so I don't think freezing valves are much of an issue. That may well not be the case for the Pilatus.
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From the SIMCOM manual:

"Air pressure for inflation and vacuum for deflation is supplied to the boots via five ejector flow-control valves installed in the right wing root. Each control valve features an air inlet, air outlet, dump outlet, and a solenoid which controls the direction of engine bleed air flow through it as determined by the timer. An in-line pressure regulator reduces bleed air pressure to that which is suitable for system operation (14 PSI nominal). The pressure regulator features an integral 18 PSI relief valve which prevents system overpressurization. An in-line water separator functions to remove moisture from the bleed air supply before passing through the control valves."

Indication that the system is working involves looking out the window. If there is a failure a CAWS panel annunciator illuminates to let you know the system's failed.

2BEER said:
Could it be that when flying in icing conditions, that the engine is operating with the inertial separator in bypass and it's "stealing" some of the bleed from the boots? Like I said, I don't know anything about the the PT-6 installation in the PC-12, but it was just a though I had. I'm probably wrong.
Click to expand...

No, that isn't how it works. Opening the separator would cause I slight loss in power but would have little to no effect on the bleed air supply.
 
We are getting the failure on the ground and in the air intermittently. I stood outside the plane the other day ands watched all of the boots inflate properly....and we still got a fail light 40% of the time. So it might be a light or low pressure. Much easier to diagnose when one of the boots fails to inflate!
 
I talked to a guy today that manages two PC12s (one /45 the other a /47) and he said that he's never had this problem on either aircraft. He did recommend to call Skytech in UZA and ask for the mechanic that use to work for Pilatus in Switzerland. I guess the guy was a director at Pilatus and knows the aircraft inside and out very well.
 
I'm not familiar with the PC-12 but some systems i've worked on apply a vacuum to the boots when they're not inflated, if the boots inflate and the fail indication comes on right after they deflate it can indicate a leak somewhere. Also if the PC-12 has a movable horizontal stab it may also have flexible hoses for the boots, i've seen these deteriorate over time as well. knot4u
 
It happens all the time on the 3 that I fly. 99% of the time it's a false alarm and the boots still inflate even though you get the failed message. It's a PITA, and there is no "fix" from Pilatus. We are told to just leave them running before we think it could be icing conditions and let it run to get the moisture out of the system, but I'm not so convinced it's moisture. There have been plenty of times when I've had the boots on way before freezing and cruized in -20 with the boots running for 30 minutes and then get a fail light, but the boots still are inflated. My best edumacated guess is a pressure switch problem for whatever of the 5 cycles it's on.
 
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