What Ice Really Looks Like

[Ted]

The other night I was flying back to Williamsport in the Aztec. There was a thin cloud layer for about the last 75 miles or so that I was in the very tops of at 6000 ft. In the winter I like to fly in these layers a bit to keep myself aware of ice and also give my equipment a good real-world test with lots of outs to make sure that it all works properly. Prop heat and windshield heat did their jobs. Every now and then a small chunk of ice would come off the props and hit the nose. The first time this happened to me (around a year ago or so) it was surprising, since it sounds like you got hit by a rock. The hot plate on the windshield mostly did its job, but those things aren't as powerful as I'd really like them to be.

Then I went to go hit the boots, and nothing happened. Hmm. The little light went on that indicated that the boots should be working, but they didn't expand. Well, that's not what's supposed to happen. Good thing I test this stuff out in appropriate situations. I got out of the icing layer by climbing. As Williamsport was close by this point, it didn't make sense to divert, so I kept going. Losing about 10 kts or so, I opted to increase the power to regain the speed. Flap and gear extensions were done at altitude in VMC to allow recovery in case of any problems due to the ice disrupting the airfoil (especially with flaps and/or gear down), and I went faster than normal on final until I was close over the ground so that if the wings stalled that they would do so and only result in a hard landing.

This was a non-event in the Aztec, as its aerodynamics resembling a brick are difficult to make any worse. The 310 would probably not have dealt with this as well due to its hotter wing, but still would have been able to deal with it, especially with the extra power. Williamsport's runways are long enough that coming in fast doesn't present a problem, I was able to be stopped well in time to make my turnoff to the FBO. Even though this was a non-event, it's a good example of why if you have de-ice equipment it's important to test (much better to find this problem out now than in a bad situation), and if you don't, to stay out of potential icing conditions.

I thought I'd share this story and the pictures. When I was first learning about icing I had no idea what it looked like when it built on a plane, and would have appreciated having some pictures and descriptions of how it works, so hopefully some people on here will learn from it. This ice built up from probably about a 15 minute exposure, including initial build-up, diagnosis of why things weren't working, and then going back thorugh the layer as I shot the ILS back into home. This is pretty typical of what I have seen at night at these temperatures, understanding that all icing situations are different depending on weather conditions. The total buildup was a bit under 1" on the wings. The little circles on the spinners are also common in my experience. It was convenient that the ice also covered up the worn out spot on the nose!

We diagnosed the system over the weekend and found that one of my boots, which was degrading but still functioning, finally gave out with too many leaks to maintain pressure in the system and is in need of replacement. It will get done at the next 100-hour, which is (fortunately), coming up soon.

Pictures below:

I hope that you all find this educational. Be careful up there this time of year!

 

[dmccormack]

Interesting write up and informative pictures!!

Question -- why did you extend flaps at all?

 

[Ted]

Interesting write up and informative pictures!!

Thanks!

Question -- why did you extend flaps at all?

Leaving them up was an option and I considered it. For one, I wanted to see what it would do in a controlled situation (answer: nothing different from normal). For two, I definitely wanted to have the gear down before descending in case that created any problems. Lastly, without flaps the Aztec will actually tend to gain a good sum of speed in a descent, and I didn't want that combination with the gear down. While exceeding gear speed is fine by me if the wings are trying to stall (priorities here), I'll try to avoid it if at all possible.

 

[dmccormack]

Leaving them up was an option and I considered it. For one, I wanted to see what it would do in a controlled situation (answer: nothing different from normal). For two, I definitely wanted to have the gear down before descending in case that created any problems. Lastly, without flaps the Aztec will actually tend to gain a good sum of speed in a descent, and I didn't want that combination with the gear down. While exceeding gear speed is fine by me if the wings are trying to stall (priorities here), I'll try to avoid it if at all possible.

OK -- I was taught by a fairly conservative 2000+ hour P210 guy that flaps are off the menu once icing is suspected or confirmed. I'm sure it's different for each airframe.

I haven't been doing much IMC lately so it's all academic right now.

 

[TMetzinger]

Very nice write-up, Ted, and a very good job of handling the situation! That sort of thinking (get out of the ice, test the effect of the existing ice on the airplane in VMC at a safe altitude) is what needs to be instilled in more pilots.

BZ!

 

[Ted]

OK -- I was taught by a fairly conservative 2000+ hour P210 guy that flaps are off the menu once icing is suspected or confirmed. I'm sure it's different for each airframe.

I would agree that no flaps is the conservative route, and that is a good option in many cases. But as with anything, it depends. The airframe will have a significant factor, as all airfoils and flap designs will respond differently. The P210 and the Aztec are also pretty draggy aircraft.

For me, coming up with any hard and fast rules for flying is pretty difficult to do. Each situation is different and could warrant a different approach to ensure a safe landing. Let's say that I had gotten the same situation in the 310. Well, it is a hotter aircraft than the Aztec by a good margin. To that extent, it will really gain speed in a descent without flaps, which it then doesn't want to scrub off. I don't want to add flaps or try a slip low to the ground, and I don't want to come in too hot and go off the end of the runway if I can avoid it. Obviously running off the end of the runway is preferable to getting into a stall/spin and crashing, but I think we all can agree the best option is a controlled, non-event landing if it's possible. So if I were in the 310, I would have run the same course of action. Altitude is your friend. In this case, I was about 5500 AGL, plenty of time to recover from a problem.

It should be noted that in all previous icing situations I've been in, the only ice I've landed with has been on the parts of the plane that don't have boots, and that has always been a definitive non-event. Typically, though, it almost entirely comes off by the time I'm on final. If it's about +3C on the approach, that by itself can be enough to melt it all off. Even if it's below freezing, the right situations can get most of it to come off.

I haven't been doing much IMC lately so it's all academic right now.

Well, given that you don't fly any de-iced aircraft (to my knowledge - I may be wrong) that seems like a smart move. But if you want to hop on over to Williamsport on a good learning day...

Very nice write-up, Ted, and a very good job of handling the situation! That sort of thinking (get out of the ice, test the effect of the existing ice on the airplane in VMC at a safe altitude) is what needs to be instilled in more pilots.

BZ!

Thanks, Tim. Just handling the situation as made sense. Like I said, it's the kind of write-up that would've been useful for me when I was first learning. Hopefully someone else will find this information useful.

 

[dmccormack]

Well, given that you don't fly any de-iced aircraft (to my knowledge - I may be wrong) that seems like a smart move. But if you want to hop on over to Williamsport on a good learning day...

No FIKI birds for me, though I may have flown IMC in icing conditions in non-FIKI.

B)

Anyway, boots on the Chief will put me way over MGW.

 

[Ted]

Anyway, boots on the Chief will put me way over MGW.

Not to mention the fact that the Chief barely climbs as-is, much less with a load of ice on it.

 

[dmccormack]

Not to mention the fact that the Chief barely climbs as-is, much less with a load of ice on it.

Climb? When?

I think of it more as a gradual upslope powered glide.

 

[ScottM]

Neat write up Ted.

I saw a 172 with that amount of ice on it at the ramp where I used to fly out of. I think he may have had a higher pucker factor than what you seemingly had.

So why did the other boots not work? It seems with a few one way valves and mechanical pressure regulators having one boot fail would not lead to all boots failing. Also how many AMUs to repair?

 

[ntbjounin]

sweet pics ted! i guess i wont post my pics of measly light rime on a TN182RG at 12000.

I wanted to say in it for the same reasons you did b/c I knew the cloud bases were 1000ft below me. Plenty of vmc to work with any problems.

I wanted to see what it was like, and then take a pic... but I saw some ice building on the fuel vent, and thought it was probably time to descend.

BTW when you said you put the flaps and gear down in VMC i was thinking AT VMC and like, uhhh Ted you're goin a little slow there! you must have ALOT OF ICE! hahaha

 

[CJones]

I like the idea of getting real-world education of icing in a controlled environment. The idea that "I just won't fly if there is ANY possibility of ice" 1.) Limits your flying abilities in IMC and 2.) Gives a false sense of security because ice can rear its ugly head when you least expect it. Going through the practice of dealing with ice in a controlled environment with plenty of 'outs' is a good idea in my book.

I have had 'controlled' encounters with ice a few times. That knowledge came in handy last year while flying to New York. We were buzzing along in the clouds with no problems then BOOM windscreen when hazy, I looked out back and could see ice building on the vertical stab. There were no forecasts for ice. Temp had been safe throughout our flight. We simply hit a pocket of ice that wasn't expected. And it was building fast. Due to my previous experience with ice, I had an idea of what the RV would safely tolerate (although I have never 'tested to failure'). I knew I was reaching my limit quickly, so I informed ATC that I was descending due to ice. I'm pretty sure that if I hadn't had any 'controlled' experience with ice, I would have freaked out pretty hard because of the surprise encounter.

Thanks for the pics and write-up.

 

[Ted]

Neat write up Ted.

I saw a 172 with that amount of ice on it at the ramp where I used to fly out of. I think he may have had a higher pucker factor than what you seemingly had.

I can't imagine being too thrilled with the situation if I had been in a 172, either. Although one thing that's happened to me over the past 1000 hours is that it's gotten to the point where nothing gets my blood pressure up. I just look at the situation, go "Hmm. Well, that's not good," act accordingly, and that's it. Although then again I try to fix the problem before it gets to the point of trying to kill me.

So why did the other boots not work? It seems with a few one way valves and mechanical pressure regulators having one boot fail would not lead to all boots failing. Also how many AMUs to repair?

My understanding of the system is that basically one leaky boot will cause the whole system pressure to drop. Remember that the boots are powered by the engine-driven vacuum pumps. Each leak will reduce the pressure in the system, and at a certain point, the pressure will be too low to allow the boots to expand. I would also suspect a gradual degredation overall where lower pressure would only blow off certain ice.

The boot that needs to be replaced is about $1500, and then labor to put it on. Fortunately, the other boots are in good shape. Hope it stays that way.

 

[CJones]

So why did the other boots not work? It seems with a few one way valves and mechanical pressure regulators having one boot fail would not lead to all boots failing. Also how many AMUs to repair?

How would the plane handle with one wing being de-iced and the other not? Obviously at some point you just want to get any weight off you can, but what happens to handling characteristics by having one wing iced and one free under non-emergency icing conditions?

Not a rhetorical question. Honestly asking.

 

[Ted]

How would the plane handle with one wing being de-iced and the other not? Obviously at some point you just want to get any weight off you can, but what happens to handling characteristics by having one wing iced and one free under non-emergency icing conditions?

Not a rhetorical question. Honestly asking.

Like anything else, "It depends." At that point, you'll have two different airfoil designs that will likely behave differently. I've heard different schools of thought on whether or not to continue blowing boots if one of them isn't working.

My instructor said one time he landed with about 1.5" of ice on one wing and no ice on the other (boot failure). On his Aztec, it made no difference. That said, he still landed fast to make sure of it.

 

[tonycondon]

i think i'd rather have symmetry

 

[steingar]

What is the readout for boot inflation? Is it that you see the boots inflate, or that you see ice coming off the wing? I ask only because it would seem more prudent to test the boots in cruise when ice isn't expected, but don't know if that can be reasonably accomplished.

 

[dmccormack]

I like the idea of getting real-world education of icing in a controlled environment. The idea that "I just won't fly if there is ANY possibility of ice" 1.) Limits your flying abilities in IMC and 2.) Gives a false sense of security because ice can rear its ugly head when you least expect it. Going through the practice of dealing with ice in a controlled environment with plenty of 'outs' is a good idea in my book.

Unfortunately I don't think there's a good formula that can distinguish between "controlled" and "uncontrolled" icing encounter in a non-FIKI airplane.

 

[ScottM]

How would the plane handle with one wing being de-iced and the other not? Obviously at some point you just want to get any weight off you can, but what happens to handling characteristics by having one wing iced and one free under non-emergency icing conditions?

Not a rhetorical question. Honestly asking.

That is a good point and I am not sure what that would do. I would think it would need to be tested on a variety of airfoil designs. I would think that it asymmetry would not be an issue if say the lest elevator boot failed but you still wanted the main wings and rudder boots to continue to operate.

 

[tonycondon]

What is the readout for boot inflation? Is it that you see the boots inflate, or that you see ice coming off the wing? I ask only because it would seem more prudent to test the boots in cruise when ice isn't expected, but don't know if that can be reasonably accomplished.

you can see the boots inflate, at least on the 421 I flew you could. we would usually test them a few times a month just to make sure everything was still working.

 

[Ted]

What is the readout for boot inflation? Is it that you see the boots inflate, or that you see ice coming off the wing? I ask only because it would seem more prudent to test the boots in cruise when ice isn't expected, but don't know if that can be reasonably accomplished.

you can see the boots inflate, at least on the 421 I flew you could. we would usually test them a few times a month just to make sure everything was still working.

Tony is correct. You see the boots visually inflate, and I do this test at least monthly (more often in icing season). However, the last time I tested it under normal conditions, it worked fine. That tells me the leaks on the boot were just enough to be on the edge of functioning. It takes less pressure to inflate a boot without ice on it than with ice on it.

As is often the case, laboratory experiments and practice may have different results.

 

[steingar]

Thanks guys. Sorry to be dumb.

 

[Arbiter419]

Wow, that's pretty amazing in a very humbling way. Thanks for the post!

 

[gismo]

Good story and good of you to share it and the pix.

WRT flaps, IMO lowering them early accomplishes nothing unless you also slow to near touchdown speed since that's when the tail is most likely to stall. Personally in your case I'd probably have put in 10 degrees on short final (being ready to retract at the first sign of trouble) or left them up. You do need to carry more speed on approach/landing just for the ice and more on top of that if your flaps are up but if the runway is at least twice what you'd normally need the extra speed won't be a problem. Dropping 10 flaps helps a lot with the speed and isn't likely to cause a tail stall unless you're really iced up (you weren't).

On the asymmetric deice issue I'd cycle them if they were doing any good at all. For one thing getting rid of any ice will reduce drag, drag that could prevent you from maintaining enough airspeed to keep the unprotected surface flying. In ice speed is almost always beneficial so I'd hate to give any up. Also, boots in every system I've seen are plumbed so that asymmetrical deployment is nearly impossible. Typically on small planes like mine and yours all boots are connected together and inflate simultaneously. On larger airplanes the boots are split into two or more sections that cycle sequentially but the sections are always balanced AFaIK (e.g. both wings then all tail surfaces or inboard wings, outboard wings, tail). A leak on one side of one section might make that side slightly less effective but as long as the leak is small compared to the ID of the tubing connecting the sides the difference in pressure from one side to the other will be minimal. And if the leak is large, neither side will do much (as I think you found out). Either way the ice accumulation shouldn't be all that different from one side to the other.

Another point to consider both when cycling the boots to test is that boot operation is stressful for the pumps. Therefore I wouldn't test them real often (once per flight should be enough). Also when there's a leak, the cycle will last longer if termination is based on reaching a certain pressure (mine work that way) and that meas a lot of extra stress on the pumps. Same for inflating the boots when the engines aren't spinning at cruise RPM so it's better to test them in flight than on the ground if safety permits and if you do test on the ground, do it at your runnup RPM not idle.

Finally, there should be a way to detect leaks before they become critical. Many systems have a pressure gauge which should reach a POH specified pressure during the cycle. The rate of pressure rise should also give a clue if you're familiar with the airplane's normal behavior. My airplane has no pressure gauge but the time it takes for the pressure to build enough to trigger the end of the cycle gets noticeably longer when there's a small leak.

 

[Everskyward]

i think i'd rather have symmetry

Me too. The checklist for the CE-680 would indicate that as well. If you only have a bleed air source on one side and the crossflow valve fails shut you're supposed to turn off all the wing anti-ice.

I also remember reading an accident report where a Challenger took off with frost on the wings but what made it worse was that the frost on one side was partially defrosted because the APU exhaust was on that side.

http://www.caa.co.uk/docs/33/factor200439.pdf

 

[GMascelli]

Ted,

Thanks for sharing the info.....good stuff for this new instrument pilot.

 

[AdamZ]

Next time try to make better use of the ice by bringing a shaker, some olives, vodka and vermouth.

 

[Ted]

Next time try to make better use of the ice by bringing a shaker, some olives, vodka and vermouth.

My preference is tequila and lime.

 

[vontresc]

Next time try to make better use of the ice by bringing a shaker, some olives, gin and vermouth.

FTFY

Vodka Martinis are the work of the devil...

 

[Aztec Driver]

Ted, I'd much rather have your "controlled encounter" in ice than my first "real" encounter. I had had trace amounts prior to this that were non events, just climbed or descended to get out. But this one encounter scared the crap out of me. I was pilot flying, but not PIC. I would have delayed coming down, as there was no forecast of ice at the altitude we were at, but the PIC wanted to make sure we could descend safely. My thought on that was if we had waited to descend, we could have found out close to our destination and not had to divert. Anyway, an Aztec handles ice very well. I allowed a little extra speed and did not deploy flaps, and, thankfully, we were able to stop on the ice covered runway.

I had some ice in the Aerostar yesterday. They don't handle ice nearly as well. The windshield deice is juat a deice solution sprayed onto the windshield. The airstream throws it off to the left so you have to tilt your head to see anything in front of you. Luckily the windshield cleared before I landed. The boots didn't, but there was not a lot on them. That was the first time I ever heard the ice smacking the fuselage from the props.

 

[Ted]

I'd suspect the Aerostar is worse than the 310 in ice, which doesn't speak well for it. Unfortunately the 310 I fly has nothing for the windshield. It's strictly incidental icing.

Like most things in flying, you end up learning a lot of icing on your own. I'd tried to get more time with my instructor in icing first, but ended up never getting anything more than a little frosting. A little preparation and common sense goes a long way.

 

[Let'sgoflying!]

on my cj type ride the dpe asked that question; its not in our book but staying symmetrical was the correct answer.

I wonder if any of the sims provide realistic feel for when a light a/c is in icing? (are there any decent sims for light a/c at all?)

 

[Capt.Crash'n'Burn]

For ****s and giggles, I decided to look up your N number..

Owner: Aztruck Air LLC.

 

[Ted]

For ****s and giggles, I decided to look up your N number..

Owner: Aztruck Air LLC.

Yep. That was intentional.

 

[AdamZ]

One thing I have been told about Ice, think it may have been Dr. Bruce its that Ice is rarely the same. Some times it will be trace and stay trace and sometimes it will build slowly and sometimes it will go from trace to really bad in no time flat.

 

[ajstoner21]

OK -- I was taught by a fairly conservative 2000+ hour P210 guy that flaps are off the menu once icing is suspected or confirmed. I'm sure it's different for each airframe.

I haven't been doing much IMC lately so it's all academic right now.

The reason to avoid flaps during an icing encounter is because, if the airplane is still flying, don't "mess" with it.

When you deploy flaps, it'll create a nose down pitching moment due to increased lift on the wings (CG infront of Center of Pressure), requiring additional download on the tail. Ice typically builds up on the tail first due to thinner leading edges, and if you demand more download/lift out of the tail, you could stall the tail due to diminished aerodynamic ability/shape resulting in a unrecoverable dive (unless you get lucky, and the ice falls off).

 

[ajstoner21]

I agree that is a very nice write up. Great pictures!

 

[Ted]

One thing I have been told about Ice, think it may have been Dr. Bruce its that Ice is rarely the same. Some times it will be trace and stay trace and sometimes it will build slowly and sometimes it will go from trace to really bad in no time flat.

I'd agree with that statement. It all depends on what's going on with the weather. If you're flying through rain you might not notice it. When it's forming as ice, well, you notice it more.

When you deploy flaps, it'll create a nose down pitching moment due to increased lift on the wings (CG infront of Center of Pressure), requiring additional download on the tail. Ice typically builds up on the tail first due to thinner leading edges, and if you demand more download/lift out of the tail, you could stall the tail due to diminished aerodynamic ability/shape resulting in a unrecoverable dive (unless you get lucky, and the ice falls off).

Depending on the plane, flaps can produce a pitch up or pitch down moment. The Aztec and 310 both produce pitch up moments with the addition of flaps. The Mooney and Lancair 360 produce pitch down moments with the addition of flaps.

 

[DutchessFlier]

Ted: Great writeup and an excellent lesson for me, and the responses were informative as well...thanks. Ice scares the crap outta me, and I have a serious respect for it. Unfortunately, in the Northeast, it's a fact of life all the time this part of the year. My CFII takes me into it when we can, just a frosting, and the first time the windscreen frosted over I asked if we could log it as actual? He laughed his ass off in the plane. I was not amused...

 

[Ted]

Ice is a fact of life, but that doesn't mean to just go fly in it with whatever airplane you have. In your 172? Bad idea. I think you know this already, just want to emphasize it. Frosting on the windshield can happen in VMC under certain conditions. By itself, that can still be problematic, but typically for me has gone away by the time I'm on or near the ground.