Frozen flight controls

[Posthumane]

I recently went on a late evening flight in my 172A. It was one of the few days of late with clear weather, the rest of the week we'd had flurries and quite cold temps. This evening the temp was -15C on the ground. It took almost 3 hours to get the airplane going from when I left the house, including digging it out of the snow (the plow clears the taxiway to the parking area, but leaves a big ridge of plowed snow in front of all the airplanes), preheating the engine with a forced air propane heater, unsticking a frozen wheel, etc.

After we eventually got flying I found that just 2000 ft up the temperature was +3C. I expected stable air and a possible inversion due to the forecast and because of the plumes of steam rising from local factories that just stopped and went horizontal a little ways up, but didn't think it would be that much of a change. Anyway, everything worked fine for most of the flight but as I approached to land, descending to circuit altitude, I found that my trim had froze. The wheel moved fine, but I could feel that it was just stretching the cable a bit as I moved it rather than moving the control surface. When I went to put the flaps down I found that they too had frozen and no amount of pulling on the handle would get them to budge.

Neither of these things were emergencies by themselves, but I became a little worried about the primary flight controls freezing on the way down. I kept them moving a little bit to try to prevent that and landed uneventfully. Is there any way to prevent this kind of thing from happening? There was no icing forecast, and no visible accumulation anywhere on the airframe.

[Hedley]

Park it in a heated hangar and let the ice melt and the water drain out of it.

I had to land a Pitts once with a jammed elevator, but that was in Alabama in the summer and it sure wasn't ice causing the problem.

[Beefitarian]

I had to land a Pitts once with a jammed elevator, but that was in Alabama in the summer and it sure wasn't ice causing the problem.

Bird's nest?

[Posthumane]

Thanks Hedley, that is certainly the best solution and what I would like to do (would make sooo many things easier), but it's not always a viable option at small airports. So, further to that, is there any other way to prevent that besides parking it indoors?

On a related note, I've determined in recent months that being a private pilot and aircraft owner sometimes requires a lot more dedication and enthusiasm towards aviation than being a commercial pilot. It's one thing to freeze your ass when you're getting paid for it and have aspirations to move up to bigger and better, but it's quite another to do it just to fly around for the hell of it and have to pay to do it. I think after all that effort it was still worth it though.

EDIT: Also, is there anything you can do while in flight once this has started to happen? Obviously one can land with limited control, but it's far from the ideal scenario.

[Beefitarian]

I'd be cautious about this but, you might be able to set up one of those tent garages on a mild day and get it warm enough with your "forced air propane heater." Might have to do it in parts ie. one wing at a time.

[Hedley]

Not a bird's nest - I would have just mashed it to pieces.

It was a BNC T connector in the tail. Not sure why it was there in the first place, but the tail of an aerobatic airplane seems to fill up with junk. This is ok if you only fly positive G, but if you push a little negative G, the junk floats up and can lock up the push/pull tube bellcrank.

A friend of mine almost died a while back at an airshow when a 10-32 machine screw did exactly that. It perfectly fit into the elevator bellcrank, and during a low altitude vertical downline, he had no elevator. Oops. Second time it happened to him, actually. First time was a set of keys. He did a really nice double outside snap on a 45 up after takeoff, and that's probably what shook the 10-32 screw up into the mechanism.

After he landed, I took the tail apart and we found the 10-32 screw.

Flight control failure certainly is interesting. Ask any B737 pilot about rudder reversal from shock cooling the hydraulic actuator.

[Hedley]

is there any other way to prevent that besides parking it indoors?

Good question. You could try spraying the aircraft down with a really hot 50/50 mix of water and radiator fluid, even though the surfaces are clean, to try to lower the freezing point of the trapped/hidden ice/water. I dunno, though. Pretty sketchy.

Loss of flight control authority is pretty serious. Ask the DHL guys who lost their hydraulics in an A300 after being hit by a shoulder-fired SAM over Iraq.

[172PIC]

What about when you put a plane in the hanger and there's still water inside. You can move controls around to let most of it pour out, wipe it down etc. but is there a risk of water on the control cables etc. freezing them in place?

[photofly]

When I went to put the flaps down I found that they too had frozen and no amount of pulling on the handle would get them to budge.

Doesn't the 172A have electric flaps?

I had the flaps "freeze" up on a 182 about a month ago. There was no visible moisture around, and the ground temp was well below freezing, before take off, when the flaps operated fine. After landing - still nada, until about 30 minutes later when they were again ok.

My AME suggested that perhaps they'd be lubricated with the wrong kind of grease which had gone hard at altitude. Other than that, a mystery.

[Blakey]

When I went to put the flaps down I found that they too had frozen and no amount of pulling on the handle would get them to budge.

Doesn't the 172A have electric flaps?

Nope. They had proper (Manual) flap actuators until 1964! They work a lot better on floats.

[burhead1]

Had the same problem with mine the beginning of February, the plane is tied down out side and it too is out in the elements. I think its time to find a hanger, I would recommend the same to you. I lost almost all my aileron and when i attempted to crank the trim, the handle came off in my hand LOL. Seems i broke the sheer pin. I was a little bothered when that happened because i figured i could have flown with the trim.
I still had elevator and could move the rudder 3-4" left and right.

Not sure if using something like wd40 on say the hinge pins would help as it will displace the water. I would talk to a AME see if you can use it and where.

[Hedley]

using something like wd40 on say the hinge pins

Please don't use WD40 on any moving parts of an airplane, unless it is an emergency, or rented from someone you really don't like very much. WD40 is an abrasive dessicant.

[trey kule]

the heated hangar is really your best option, other than putting a herman nelson (not a construction heater) on it...the heli guys use a surplus parachute to make a tent. but you would have to spend literally hours doing that to get everything to properly dry out.

Now as to WD -40..It got me thinking about the grease the AMO is using on your cables and flap hinges. Just a thought but maybe to much or to heavy a grease..and that is purely a guess. I have seen AMES put grease on with the theory that if a little is good , a huge amount has to be better. It does gum up.Now I always thought the WD in WD 40 stood for water displacement and it was originally formulated to do just that. Perhaps I am wrong. In any event there are other lubricants Lp types that are used on aircraft if you prefer, and after all should be properly lubricated, because wd40 and other, generally are not lubricants
My personal favorite is mouse milk. Good penetration and lubrication, but surfaces have to be dry before putting it on.

The WD 40 caution got my attention.....so

The long-term active ingredient is a non-volatile, viscous oil which remains on the surface, providing lubrication and protection from moisture. This is diluted with a volatile hydrocarbon to give a low viscosity fluid which can be sprayed and thus penetrate crevices. The volatile hydrocarbon then evaporates, leaving the oil behind. A propellant (originally a low-molecular weight hydrocarbon, now carbon dioxide) provides gas pressure in the can to force the liquid through the spray nozzle, then itself diffuses away.

These properties make the product useful in both home and commercial fields; lubricating and loosening joints and hinges, removing dirt and residue, extricating stuck screws and bolts, and preventing rust are common usages. The product also may be useful in displacing moisture

I have seen this used for years without any problems in drying out hinges etc.
The problem that usually results is after cleaning and spraying no one regreases a part and it is not a good long term lubricant. The only people I ever heard previously dissuading its use where those interested in selling a similar prodcut...but each to their own.

[Hedley]

Grease does indeed dry up and gum up over time. However, a squirt of Corrosion-X will soften it up nicely again.

[trey kule]

I love corrossion X...never used it for that. Will it work in the cold on his plane?
Is this a s topgap measure rather than cleaning and regreasing, or a regular way to replace cleaning and regreasing?

[Hedley]

Will it work in the cold on his plane?

Probably not terribly well.

Is this a stopgap measure rather than cleaning and regreasing, or a regular way to replace cleaning and regreasing?

A squirt of Corrosion-X is NOT a substitute for cleaning & re-greasing, merely a simple way to soften clean grease which has dried out and hardened up over time.

[x-wind]

Its a case specific resolution but if you'd deployed a bit of flaps coming back down into the cold air maybe they wouldn't have froze to the wing.

Doesn't solve the trim problem or your flight control concerns though.

[KK7]

Be cautious when de-icing using a heated hangar, or if you use the tent idea with a propane heater to heat the plane as whole. You have to make sure to keep the plane in the hangar until not only the ice and snow has melted, but the melted water has evaporated. Otherwise you run a higher risk of jammed controls due to freezing from water running into the cracks around the controls, then refreezing when you take it outside. I suggest as the airplane is heating up in the hangar, you are continuously removing every bit of ice and snow you can find so that it melts on the floor, and not on your plane, and this reduces the amount of time you need to thaw everything out.

What I used to do in the absence of a hangar is put the flaps down and have someone move the controls and trims full deflection to try to get any bits of ice and snow between them, but this only solves whatever is on the exterior of the aircraft. There are many places ice can hide inside an airplane.

[Hedley]

the melted water has evaporated

In my experience that isn't too hard. Let's say the winter OAT is -15C with dewpoint of -20C (eg a normal 5 degree dewpoint spread). That's pretty dry air - it can't hold any moisture in suspension.

If you heat the hangar up to +20C you now have a FORTY degree dewpoint spread which is enormous. That air can hold a lot of evaporating moisture. A little bit of air circulation from outside the hangar to inside will assure that the air is quite dry and warm.

If you have a hermetically sealed R2000 hangar - never seen or heard of such at thing in 35 years of flying, but I suppose it's theoretically possible - you will have to ensure some air cycling, or turn on the de-humidifier which you must have for summer anyways.

[Posthumane]

In this case I don't think it was the flaps themselves freezing to the wings, but rather something in the cable/bellcrank/pushrod mechanism. The reason I say that is that I could wiggle the flaps slightly on the ground - there was a little bit of play in the tracks. However, they wouldn't come down and reefing on the handle was just stretching the cable. The plane is due for an annual within a week so it is going into a warm hangar, and I'll be sure to call some extra attention to regreasing the control cables.

I don't think it would take too long to evaporate the water from the aircraft in a heated hangar; they typically don't have humidifiers on the furnaces like a house would. I suppose if I had flown for a few hours in the +3C air it might have helped as well, but I went from a -15C surface temp up to the warmer air for a short period, then back down.

[Expat]

The front of the flaps rub against the upper wing skin, and some left over ice or snow probably just melted enough, then froze on descent to create a shear bond. Nothing that unusual.