icing?

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savashinsky
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icing?

Post by savashinsky »

Hello, DiamondAviators!

My name is Oleg Savashinsky. I'm a pilot from Belarus and I fly Diamond DA40. I have a question.

It was on FL100 in clouds. Temperature - around 0C. 3h20m after take-off I noticed small oscillations of IAS. I supposed that turbulence was the reason. However, there was something unusual for me in these oscillation and I kept shooting a glance from time to time on the airspeed indicator. Also I looked on the root of the wing: there was a small trace of icing. I coudn't definitely see the entire surface of the wing - it was blurred a little in clouds. No noticable vibration or changes in engine sound. I thought this ammount of ice was not very important, sometimes I had more ice and nothing strange happened, TAS dropped down around 20 kts and that's all, so I continued my flight on FL100.

Finally speed dropped to 66 knots very quickly (you could see that moment in the attached picture). I immediately disengage the autopilot, went down and descended to 8 000 feet. When I leveled the aircraft IAS was around its typical value. Later I successfully landed at EDLP. If it was ice, I thought, how could it melt so quickly?

I'd be very appreciate it if you share with me your ideas about possible reasons.

Thanks and regards
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AndrewM
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Re: icing?

Post by AndrewM »

Did you have your pitot heat engaged?
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savashinsky
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Re: icing?

Post by savashinsky »

No, and it was my mistake. I spent a lot of time checking IAS and forgot about pitot heating. But later I checked 2 min distances in the low speed region and before. That confirmed low speed. Apart from that I checked CHT, and they were slowly going up.
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Re: icing?

Post by Lou »

If you were at 0 degrees C at 10,000, you would typically pickup 4 degrees in the descent and be at +4 at 8000. In my experience ice melts very quickly at 4 degrees and so a small amount of pitot icing would dissipate quickly too.

I was taught that there is never a reason not to fly without pitot heat. Maybe others have a different perspective? I use it even when there is practically no risk at all.
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Re: icing?

Post by Colin »

46, pitot heat on if there is visible moisture. 36, turn it on anyway, in case I forget.
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Re: icing?

Post by Antoine »

Oleg thank you for being so open about it.

Looking at your data I believe that you had a frozen pitot/static system AND airframe icing.
The curves show that both speed and altitude data are not smooth. Either you had heavy turbulence (which you said is not the case) or your pitot static system was clogged by ice.

I strongly recommend that you make it a rule to switch pitot heat on as soon as you approach -3 C.
This costs nothing and will at least ensure that you have no pitot icing.
Then if you inadvertently enter icing, you should follow the icing checklist. I do not remember exactly because I no longer fly a DA40. Certainly this includes switching to alternate air for both the engine and the instruments.

You seem to be very relaxed about being in icing. Forgive the pun, but this is Russian roulette.
A DA40 has laminar flow wings and a very streamlined fuselage.
The aircraft is not designed to deal with icing. Anything can happen from frozen controls to a stalled engine etc... So you are now a test pilot.
Therefore my other recommendation: do not take off, never, ever, if you expect icing. As the old saying goes "would I rather be down here regretting that I am not flying or up there regretting that I did fly."

We want you around for a long time. Ice is not for your aircraft and even if you got away with a few encounters, you could very well hit one that will kill you before you even understand what is happening.

Sorry of this sounds dramatic. The internet is full of sad stories, and you can see for yourself why I am being so direct. DA40 = stay well clear of icing.
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Re: icing?

Post by Rich »

There's no point in discerning which airplane type(s) can carry ice better than others. Everything has its limits. Nevertheless, one of the very few DA40 fatal accidents in the US was an icing encounter:

https://app.ntsb.gov/pdfgenerator/Repor ... L&IType=FA

You might read this as the plane was able to carry quite a bit of ice before the untimely termination. Don't.
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Lou
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Re: icing?

Post by Lou »

A little bit of ice in northern climates is unavoidable. On the weekend we went through a low layer (no published risk of icing) and came out on top with visible LE frost. It sublimated off in the morning sun.

I learned last week that many aircraft have published minimum icing speeds. Who knew? I don't think that our Diamonds are worth testing in that environment. The best policy is to minimize exposure.
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Lou
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Re: icing?

Post by Lou »

I have been thinking about this and I want to venture to say a little more. Northern Canada and Belarus are similar in climate. When I meet high time pilots here the first thing they ask me about the airplane is "how does it handle ice?" because you are going to face it. I think an absolute rule to avoid all risk of ice is not helpful.

Ice is a dangerous thing, but you can learn about the danger and manage it. Learn the types. Light rime is one thing, SLD is another. I have flown through a cloud top in July and picked up SLD. It is a sudden and dramatic encounter. On the other hand, light rime is a gradual thing.

Brief the weather always to assess icing risk: freezing level, humidity, vertical cloud formation are all risk factors that have to be accounted. A thin stratus layer at the freezing level may give light rime, but you will pass through it quickly. Autumn TCU's, rising humid air at the freezing level will be a total mess. If you perceive a risk, do you have an exit? Can you descend, or turn around? As a rule, I would say the DA40 should not be flown in hard ifr around the freezing level. Plan an altitude that is either very cold (-10 or colder) , or more than 2 degrees C.

If you encounter icing, the procedure is prop full speed, defrost, pitot heat, fly to safety. Alt air is used when impact icing blocks the engine - a very rare occurance. Alt static is used for a blocked static port.

Hope this helps.
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savashinsky
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Re: icing?

Post by savashinsky »

Hello again, guys!

Thanks for your comments.

When I was placing my post I also had an idea to show how important the word IMMEDIATELY, when POH describes pilot action in icing condition. To be honest, I didn't suspect that things could be aggravated so quickly. Sorry if what I'm saying is trivial for the most.

I supposed I had some practical knowledge in icing. I got most of them from my flights in regions more northern than Belarus. (About one of my trip:http://flugblogg.is/2017/11/22/against- ... own-plane/). I read a lot about weather and aviation. I could remember all these pictures from articles and books with a lot of huge amount of ice on wings and other parts. "Not so much", I thought, when I saw some ice on my wings. "If it keeps going, I'll go down, let's wait a little, hope I will be out of clouds in a minute". TAS was going down slowly, sometimes from 135 kts to 105 kts. Then it depends: more ice - go down, no more visible ice, no more loss of speed - waiting the sun. Sure, pitot is on, alternate static is on.

That time everything started as before. Temperature - around zero. Looked at my left wing - small traces of ice. Negligible... Then erratic speed oscillation... Sometimes IAS was on its way to the normal region. Look at the wing again - a little bit more, but still insignificant (according to my opinion). Then - unexpected 66 knots, I switched autopilot off and went down. At this moment I switched pitot heat on also. I know, a little bit later, but I was really over concentrated on this strange behaviour of the air speed indicator and on the engine sound.

My short summary:

1. I investigate all Garmin data thoroughly and I agree that most probably it was icing and pitot blockage.

2. Why I suspect that the speed was going down? Because I measured 2 min distances and the distance when IAS was supposedly low is 25% less than normal. Apart from that, CHT was rising in that period. It looks like pitch was also higher than normal.

3. Even if it would be only pitot blockage, it's also dangerous because of possible overspeed.

4. Sometimes you couldn't even estimate definitely how much of wing surface was covered with ice - dark clouds, white wing, and the picture is blurry.

5. You never know what is insignificant.
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