Flying in snow

[LateFinals]

As I look out of the window I wonder if anyone has advice about actually flying in snow. Assuming your plane has FKI capability, the winds are ok, no CB's about, and the runway is clear is there any specific advice about flying in snowy stuff more experienced pilots wish to share.

(and no I'm not planning on rushing to the airfield !)

LF

[Squawk 2650]

Roads, rivers and railways all look the same!!

Its quite cool being in cloud while its snowing!!

S
:cool:

[Genghis the Engineer]

Snow has a tendency to build up on windscreens and leading edges, restricting visibility and changing aerofoil shape. The result can be a wing with a strong disinclination to generate lift. A colleague of mine once nearly ended up a hole in a mountain in Norway in an HS780 as a result of this fascinating phenomenon - and that was supposed to be de-iced! (Anti-icing, maybe, would have worked better.)

Also, even very light snow effectively puts you into IMC (imagine flying through the old windows "stars" screensaver) and you have the idea. If it starts sticking to the windscreen, you won't see a thing (happened to me once in unforecast snow, scared the heck out of me - flew out of it on instruments and thankfully it cleared quickly).

Of course there are fully anti-iced aeroplanes which can handle this, but for the stuff most of us fly, it's likely to end in tears.

Flying *over* snow once it's stopped falling is just pretty. Things look slightly different so a little more care in navigation is needed, low level turbulence tends to be minimal and so long as the runway you use is de-iced (or you've taken appropriate care and applied necessary safety factors) it's really very safe and enjoyable.

G

[stickandrudderman]

dreaming of being in Switzerland right now!
http://www.pprune.org/private-flying/315871-fate-luck.html

[gasax]

Even the lightest amount of snow makes things VFR difficult. The transitiion from rain to snow can be pretty quick. As stated above, it builds up in some interesting places. On my Auster the wing roots, struts and over 50% of the windscreen. And that occurred in little longer than it took for me to notice the rain wasn't anymore!

Flying after a light dusting of snow can be pretty excellent. Cool, stable air, bright light and on our strip the capability to fly a couple of circuits and check the consistency of touchdown points.

Flying after a heavy dump - impossible for us. Couldn't get out of the hangar without loads of digging and the rolling resistance meant taxiing needed loads of power. And then when it thawed even more rolling resistance!

[drambuster]

Snow has a tendency to build up on windscreens and leading edges, restricting visibility and changing aerofoil shape.

Gen the Eng . . . . . . I think you're referring to ice ! According to the latest copy the the US 'Flying' magazine which happens to have an article on this very subject, they say that there is no problem flying in snow (providing it's not the wet/sleety variety that could turn to ice).

So, according to them, light to medium dry powdery snow just blows straight across the airframe without any problem.

If it gets very heavy then it can clog air intakes . . . . . . . . but at least you will have a soft landing :}

[strake]

So far, I've only really frightened myself twice in flying. One was a near miss and the other was many years ago (having just qualified), inadvertently flying into a snow shower in the circuit at Cranfield in a 172.
It was a long 10 seconds of zero viz.

[IO540]

I don't think snow brings the same risks as structural icing i.e. flight through supercooled water with the TAT being below 0C.

Snow is frozen to start with.

Snow can certainly accumulate and is thus dangerous, but would it accumulate without limit, the way ice can do? I don't know. On the rare occassions I have flown through falling snow it did not seem to be sticking at all.

My guess is that the really dangerous thing is higher up; snow is often (always?) formed when freezing rain falls into colder air, and you definitely do not want to be flying in freezing rain. One meteorologist told me that snow is always formed from freezing rain but I am no sure about this.

[Parsnip]

"According to the latest copy the the US 'Flying' magazine which happens to have an article on this very subject, they say that there is no problem flying in snow (providing it's not the wet/sleety variety that could turn to ice)."
Right so that I understand before I nip down and hire meself a Warrior
Its OK in dry snow ,but not in wet snow.
So how do these guys know when the dry snow is going to suddenly (and maybe catastrophically) turn into wet snow which on contact with the freezing cold wing will immediately turn into a sheet of nasty clear ice and bring the whole flipping lot down into a big smokey mess?
Yanks....................................................... ........

[mm_flynn]

I thought snow was just formed in clouds below zero. Certainly when skiing you can be clear on top, ski into cloud that is snowing, descend down the bottom where it is raining.

Freezing rain, I believe, needs an above 0 layer above the 0C Iso Therm so that the precipitation can be liquid and then super cool.

I don't have much snow experience, but for me, looking out the window in snow is one of the few occassions where it really looks like I am going fast!!

[wsmempson]

I flew through a light snow shower over Lyon last year, whilst transiting at FL65. The general effect was rather like those Pearl & Dean ad's which they used to show at the cinema, which is mildly disorientating; better to keep focused on the instruments and the OAT gauge...

[M609]

IO540 on the correct track here IMHO

Having flown quite a bit in snow (VFR/SVFR only), and I've never had it stick on the aircraft in any way. Now, the way the weather works up here, when the visibility in snow conditions are good enough for VFR/SVFR the temperature is not going to be close to zero, and there is not much risk of severe inversion. That way the snow in the showers (or sustained snow) is going to be dry, and will never stick to the aircraft.

When we get temperatures close to zero, naturally the snow gets "thicker" and wetter. That will stick to the airframe, but the flight visibility will be cr@ap, and you should not be flying anyway. (SVFR)
And....the met office tend to start sending out ICE Messages with MOD to SEV ice when it's like that anyway!


Now, holding time prior to departure have caught a few pilots with their pants down up here even with dry snow, cold temp. Dry snow accumulating on a warm wing during taxi does not necessarily blow off during take off, even in a C172. It can make the wing do weird things (not necessarily dangerous/critical) if you get asymmetrical coverage on top.

[Captain Smithy]

Just over a week ago, I encountered a moderate snow shower which appeared very rapidly in otherwise fine conditions. Visibility closed in very quick all around and cloudbase lowered rapidly to about 1500' but thankfully no build-up of ice at all, and we were through the shower in about 20 seconds at the most.

Wouldn't recommend it however; we had a close call with what looked like a Robin and then very quickly afterwards a microlight which both suddenly appeared straight-ahead out of the murk without any warning; obviously, like us, trying to get through the suddenly deteriorating Wx back into good conditions on the other side; nothing on frequency, just appeared dead ahead less than a mile away. All three of us squeezed in under this shower, with a lowering cloudbase and jammed between two hills. Perfect recipe for a disaster; gave me a bit of a fright.

[No_Speed_Restriction]

its like the old windows screensaver.

[Pace]

I have flown in snow many times in IMC and never had a build up from it. It is already frozen and apart from sleet or a situation where there is visible moisture and snow together would have no binding ability. But that would be more in the realms of icing conditions rather than snow itself.

At night especially with strobe lights or when you take the landing lights the effect can be very dissorientating. The flakes especially the larger they are can cause a very disturbing streaming effect. The solution is NOT to look outside but keep your eyes firmly on the instrumentation.

I can remember flying back from Scotland at night years ago in a snow storm with the added complication of severe turbulence.
The leg from inverness to Glasgow was hell on earth in a Baron and the sense of relief breaking the front with all the city lights of Glasgow was immense.

Another trip back from Ireland again at night was no problem at all although there was intense snow. The worst problem I had was driving home on the motorway where I seriously got stuck :)

One plus with flying in snow is that it will polish your paintwork like nothing you have seen and the aircraft will gleam.

Negative is visibility which as one poster said will drop badly and still give odd sensations when trying to visually land.

Ideally use an ILS and fly that to minima. Then keep your eyes fixed firmly on the landing point runway lights. Dont look sideways as that will mess up your ability to judge the glideslope. You will find yourself flying lower on the glideslope than you should be. Why I dont know.

Daytime while still a problem is not as bad as the flakes will blend more with the cloud and not have such a pronounced effect.

Pace

[Pilot DAR]

Referring to "snow" is kinda like referring to "trees". we think we know what we mean, but there are really all kings if differences one to the next. Some kinds of snow I would not even want to drive my car in, other kinds are a visual delight, and totally harmless. Then there's all the type in between.

So, when someone tells you it's snowing, all you really know for sure is that the temperature is near or below freezing, and there is precipitation. More information is required to determine if flying whatever aircraft type you have, is suitably safe.

If the temperature is well below freezing (-5 or lower), and will remain so, and you have the visibility to be safe and legal VFR, flying in snow in most aircraft would be quite safe (known icing equipment not required). Snow will not accumulate on a moving aircraft. In the last week, 4 of my 5 hours of flying have been in snow, both in the mighty Cessna 150 and the Jet Ranger. With visibilities as low as 1.5 miles in the plane, I kept my testing very close to the airport, and there was no problem. It the Jet Ranger yesterday, we landed when the visibility got to be less than a mile.

When it gets very cold (-40) you really don't get much snow. You sometimes get ice crystals suspended in the air, and the beauty can be incredible. If you're IFR in heavy snow at temperatures of -15 to -25, a static charge can build up on the airframe. I have had cases flying the Aztec, where you can put your outstretched hand up to the windshield, and "sparks" (like you see in those round glass domes) will flow from your finger tips to the windshield. It will light up the cockpit just enough to make the passenger in the back scream!

Around here we get "Snow streamers", which are very local and dense snowstorms which flow downwind off the lakes. If you have internet radar, they are easily anticipated. Before that service was available, you took your chances, because there was no way of forecasting, other than direct observations. For a well planned flight, there would be a bunch of phone calls to buddies along the route, and chatter on the radio (if you had one) along the way. A poorly planned flight, could turn out like this:

While in Sudbury, awaiting the fuelling of the Cessna 206 I was to ferry home, we were upstairs in Flight Service checking the weather. The Flight Service specialist looked out the window toward the 206, and casually asked me if it was mine. I answered “yes”. He said “well, you might want to go down and check on it, because the fuel truck which is fuelling it is on fire.” Huh!? Sure enough, I looked out, and the driver had the hood up, and flames were belching out of the engine room. We sure moved fast getting downstairs and out to the plane.

The driver had already emptied his fire extinguisher, and the fire still raged. We pushed the 206 well away from the action, and it was thankfully unaffected. The airport fire department soon arrived, and foamed the fuel truck, and that was that. No fuel.

After several hours another fuel truck arrived, and fuelled us. We were ready to go, and it was dusk…. Never mind, it was a beautifully clear evening, and I knew the route well. I was though, now regretting lending my portable nav/comm., as it would be rather handy for night flying in my otherwise Nordo Cessna 206. Oh well, hindsight will be 20/20 later!

So we launch off. I’m flying alone in the 206, following RN and JD in the IFR equipped Cessna 182. After three quarters of an hour, it was completely dark. I was following off and behind the 182, keeping the best distance I could judge from only the two nav lights and beacon. The plane itself was invisible in the dark. During one of the routine instrument checks, with the flashlight in my teeth, because I’d found that the instrument lights did not work, I noticed that my right fuel was below half. This would seem normal, except that I had taken off, and run up until now on the left only, and they do not cross feed! Fuel leak! I now selected the right tank to use what remained there, before it was lost overboard. This was not a serious problem though, as I had lots of fuel anyway. After a while, I felt the sensation of turning circles. This sensation is known to affect perception while flying instruments only. I paid more attention to my control inputs. Sure enough, if I held the controls straight, I went straight, but the 182 went away, and following it was one of my objectives! I now paid more attention to my own navigation rather than just blindly following them. The first thing I noticed was that we were at 750 feet altitude, which was alarming, because nearby Georgian Bay is at 581! Why are we less than 200 feet AGL? I turned on the landing light – snow! And lots of it. Obviously they were trying to remain VFR, though who knows why, ‘cause it was too dark to see the ground anyway! The next thing was that we were going north, instead of the south, which was our route. I surmised that they had decided to return to Sudbury, as there were no other useable airports in the area. Then we were turning east, then south, then east again…. Turning “S” turns for no good reason. All I could do was follow, I had no ability to navigate.

After what seemed an eternity, the dim lights of a town became visible through the snow. We obviously both saw them at the same time, because we both headed straight for them. Bracebridge. We’d (really they’d – I was just following) found Muskoka airport. Once in the circuit, we were clear of snow, and could see south forever. I though about keeping going, but then reminded myself of my uncertain fuel situation, and decided to land for fuel.

Once we both fuelled, and checked the weather (which was reported as just fine to the south) we elected to keep going. So we took off again. As I could follow the highway now, and was much faster, I elected to head home on my own. By the time I got to Orillia, I was back into the snow, as thick as ever! I followed the highway with great precision a few hundred feet up. They don’t put towers right in the middle of highways!

I got through, and continued south, with the city of Toronto now in sight, Pottageville was assured!

Now the runway lights at Pottageville were still powered by the reliable little Honda generator, which RN’s wife had left running for us. Sure enough, there were the lights! Excellent! I slipped in for a perfect landing, and was very relieved to be safely on the ground at home. On short final, I saw their nights 10 miles back, so I knew that they’d made it through the Orillia snow as well. I parked, and sat back to relax.

After a few minutes, I saw them come overhead, and felt the final relief. They circled for a while, then some more, and more. I could not figure out why they were not landing. I went over to my parked C150, to call them on the radio. At the same moment I heard a stream of profanity come over the radio, I clued in; the generator had quit, and there were no runway lights! There was a break in the tirade just long enough for me to report that I would get the generator going again. Problem… It needed gas. The gas truck was there, but RN had the keys in his pocket, so it would not be offering any gas for the generator ‘till he was down!

I ended up sump draining enough gas from my plane to get the generator running long enough for them to make it in safely. That night was the point at which we decided that permanent runway light power, and ARCAL was needed. The final connections began the following week!

[gasax]

Squeaky dry snow probably does n't stick. Wet mushy stuff definitely does. That is, in the UK and probably at low altitude the sort of stuff VFR fliers are most likely to run into.

Will it accumulate like ice? From my limited experience probably not, as it still seemed to be a bit mushy.

Will it freeze? Don't know but the loss of visibility is enough to mean you don't want to find out.

[Pace]

Squeaky dry snow probably does n't stick. Wet mushy stuff definitely does.

Gasax not true

Squeaky dry stuff will not stick wet mushy stuff is still wet and mushy and still will not stick any more than other visible moisture unless the temperature drops enough to freeze it on contact. At wihich point it will no longer be wet mushy stuff :)

Pace

[drambuster]

Thanks PilotDAR - that was very informative followed by a good yarn on 'how not to do it' !

You and Pace have confirmed that the image of piles of fluffy snow building up on a leading edge at 150 kts is not entirely realistic !


Drambuster


NB - Parsnip . . . . were you a member of the drama club at school by any chance? :)

[Final 3 Greens]

If you do go flying after snowfall, there is one potential gotcha.

When you do the power check (run up) the snow (or ice) can reduce the friction between the wheels and the ground and you can move quite nicely with parking and foot brakes fully applied :=

So be careful where you choose to run up.

[gasax]

Wrong Pace.

Wet mushy stuff did stick. Now it may start to freeze, but it certainly did not seem like it. It did not look like ice and it did fall off during the landing (was n't that violent really!).

But a couple of inches of accumulation on the leading edges of the struts and around the wing roots certainly got my attention.

You may want to call it something else but on at least two occasions the Auster collected wet snow and it stayed on the airframe to the ground.

[RatherBeFlying]

All come into the situation:
All >0C -- no problem
All < 0C -- no problem
Airframe > 0C ; Air < 0C -- Snow can stick to airframe; as previously noted easy to happen during taxi after leaving warm hanger
Air & airframe > 0C -- snow and ice should melt off
Air & airframe < 0C; snow >0C -- nasty
As previously noted snow showers limit forward visibility, but often there is quite good visibility down and you can use terrain for orientation. Snow showers tend to run in bands downwind; so, a crosswind course and picking thin spots will minimise time in snow showers. I really want to be able to see the ground on the other side of the band before deciding to go through. You do want to know your terrain and remember that uniform terrain without features can put you into whiteout which is a whole other topic.

[Genghis the Engineer]

There is, 'tis true, a sort of long sliding scale between dry powdery snow, via wet sticky snow, via supercooled water droplets which cause icing, to good old fashioned rain.

Some of it (around the wet sticky snow/supercooled water bit of the line) that will build up on leading edges and (particularly with wet snow windshields). Some of it is no more than an irritant and obstruction to visibility (dry snow, rain). A sub-zero airframe on the other hand will collect rain and wet snow quite effectively.

Accurate prediction of what you are going to hit, and whether it'll stick is not very easy so, personally, I would (particularly in the UK which tends to hover around freezing so wet snow is reasonably likely) not assume that snow won't build up.

G

[Granite City Flyer]

Snow building up in/on the induction intakes/filters can have you reaching for hot/alternate air. The Partenavia and Apache are 2 types I've had this issue with.

[mikegolfpapa]

IMHO the most important thing is to be totally comfortable flying in IMC; the real thing not under the hood or with screens.
You will then use only a small proportion of your brain power to actually fly the aircraft leaving loads of spare capacity to worry about, and if needs be resolve all the other problems that may or may not trouble you!

[jamestkirk]

Final 3 G's is right. I was at on a snow covered runway recently. Held the brakes with about 15% power and off we slid.

The other thing to bear in mind is landing. If the R/W is frequently cleared then fair enough. If not and there is a crosswind, you may want to lower your personal limits.

[Pace]

Wrong Pace.

Wet mushy stuff did stick.

Gasax sorry I am not wrong you explain to me scientifically how wet mushy stuff can stick unless the temp is at such a level to create icing.

You are missing the point completely. You will get ice build ups in visible moisture when the temperature hits freezing. At that point the visible moisture changes to ice and attaches it to the airframe.

Your wet mushy stuff is no different to visible moisture. You may have had what you percieved as wet mushy stuff sticking to the airframe but it WILL BE because the temp has hit a level conducive to icing so no different to flying in visible moisture.

Pace

[Pace]

Snow building up in/on the induction intakes/filters can have you reaching for hot/alternate air. The Partenavia and Apache are 2 types I've had this issue with.

Granite City Flyer

I almost posted this exception but decided not too. Yes if the snow has nowhere to go ie it hits a flat surface like a grille and doesnt pass through there is a danger that it will block the inlet.

Most aircraft dont have that sort of setup but ones which have a grill over something like an engine intake could block with snow if its unheated. The Partenavia did come to mind but that aircraft doesnt have a good reputation in any icing not just snow.

Pace

[Blues&twos]

Does snow affect the ADF?

Everything else in the world seems to, I assume snow is no different!

[Genghis the Engineer]

Probably. Snow tends to be associated with CBs, thunderstorms tend to be associated with CBs, an ADF tends to point at a TS. So, some risk of snow and ADF deflection being coincident.

G

[belowradar]

Flew through snow showers late Sunday PM and it was really cool to see the snowdrops whizzing past and straight at the windshield.

Snow showers were intense but widely spaced so plenty of options to "escape"

Temp was -5 and no icing encountered, clouds were white instead of grey

[Codger]

Snow...
Pitot Heat ON!
No, I won't go in to how I know this.

Light flurries can be a whiteout at a hundred knots. Tread carefully.

[pigboat]

The most dangerous thing about flying in snow is whiteout. It's a condition that can occur when flying over featureless terrain - a large open space or a lake, say - where the visibility is reduced by snow, the discernable horizon disappears and you are left without visual clues. The trick to is to follow the shoreline of the lake, or trees along the edge of the field. The only other option is to transition to IMC, pronto.

As for flying in snow, I used to get paid to do things like this: :D
http://i100.photobucket.com/albums/m8/Siddley-Hawker/PUPonskis.jpg

[Pilot DAR]

Yeah, okay, that stuff I saw on the news, which fell on England today... I would not be flying in that! Clue, If Heathrow is shut down, you should be too!

Seriously, every type of flying has it's own pleasures and challenges. It's up to all of us to enjoy the pleasure without being overcome by the challenge. Things like whiteout/loss of visual reference (which can happen even without the snowfall), brakes frozen solid (wheel won't turn at all) because you let them get warm, by using them, them taxiied through loose snow just before takeoff, and skis frozen to the surface, are their own hazards, and must be planned out of your flight with wisdom.

The airport I was flying from today has had twice the average seasonal snowfall this year, (presently 4.4 meters), and it's piled so high along the taxiway, that today it was hard to get the Cessna (highwing) wings between the snow banks, 'cause they won't go over any more. Now I know how the Cherokee pilots feel!

Pilot DAR

[gasax]

Pace is convinced snow does not stick to airframes. Well it might, but by then it has subtly changed to ice.

I and most other pilots have no idea at what that point is.

It is however interesting that many helicopters have limitations on flying in snow. (there is a bunch of stuff about the engines as you might expect) but the rotor systems have exposure limits to snow. So presumably the manufacturers are worried about the effect on the aerofoils. Of course I'm sure that is probably ice - but if it looks white and flurry and there is an exposure limit - it can stick.

[usedtofly]

Flying in snow (especially at night) is like watching a sci fi movie in the dark and sitting too close to the screen...........hyperspace?............warp factor 9 anyone?

:E

[Pace]

Pace is convinced snow does not stick to airframes. Well it might, but by then it has subtly changed to ice.

Gasax

With all due respect what is snow? how do snow flakes change to ice? only a liquid can change to Ice. examine a snow flake and then work out what its composure is?

On a slippery airframe snow flakes will not accumulate only as I stated in one post if there is nowhere for them to go. Ie they impact onto a thin mesh unheated grill unusual on most aircraft.

You really are digging yourself a bigger hole with each post

Pace

[Parsnip]

Drambuster NB - Parsnip . . . . were you a member of the drama club at school by any chance? http://static.pprune.org/images/smilies/smile.gif
Nah mate.... fight club... yes:E
The purpose of my post was to elicit the sort of response from the sort of more experienced here which we have sort of half reached. When does dry snow, which I understand isn't sticking to the flying surfaces, become wet enough to be a cold slurry which then freezes onto cold wings and ailerons and becomes a serious hazard. Thats all really ...on the basis that I'm highly unlikely ever to fly in the stuff I'm not sure that I need to know much more than that which "rather be flying" and "Ghengis" have posted

[Pace]

Parsnip

You have to be aware of icing potential in any flying situation where the temperatures are conducive to icing and there is visible moisture in the form of cloud or precipitation.

That is a sensible approach regardless of whether there is snow or not.
To take an aircraft with no deice/anti ice capability into such a situation is risky.

Pace

[Pilot DAR]

It is however interesting that many helicopters have limitations on flying in snow. (there is a bunch of stuff about the engines as you might expect) but the rotor systems have exposure limits to snow. So presumably the manufacturers are worried about the effect on the aerofoils. Of course I'm sure that is probably ice - but if it looks white and flurry and there is an exposure limit - it can stick.

For the four types of helicopters I fly, the only concerns about flight in snow (water which is already frozen), as opposed to icing condions (the water is acting more like a liquid, around freezing temperatures) are associated with the huge amounts of air which the turbine engines gulp, and the ease with which they can be flamed out with too much snow, under certain circumstances. And, operation close to the ground (hovering) where you can very suddenly blow up so much snow in front of you that you instantly loose all visual reference. There are no stated limitations.

Perhaps there are other types of helicopters which are not so tolerant of snow in flight, timid tropical types... We don't get them in Canada!

So we're having all of this emotional discussion about snow now, because the UK finally got some, and everyone is looking at it, talking about it, and wondering what to do with it?

Pilot DAR

[M609]

METAR 031220Z VRB01KT 2000 SHSN VV008 00/M01 Q1007

Pace: Do you mean, that with conditions as stated above, all moisture in a snowshower is frozen so solid that it will slide off everything but grilles etc on an airframe?

:ugh:

[BackPacker]

I don't know about Pace, but I would not assume that. Not without knowing the upper air temperatures, particularly the bottom 3000' or so. If there's an inversion the snow might be very, very wet and sticky, particularly if the airframe is still < 0C.

[Pace]

Pace is convinced snow does not stick to airframes. Well it might, but by then it has subtly changed to ice.


Snow does not in itself stick to airframes. Maybe I am being pedantic but it is important to understand what is actually going on.
If you examine a snow flake it is already frozen. We have all seen the pretty line drawings on postcards at Christmas of the ice crystals which form a snowflake.

Unfreeze it and it would return to a liquid.

Where the confusion lies is in the fact that only a liquid can turn to ice if frozen. You cannot change a frozen snowflake into solid ice without turning it into a liquid first.

If you have a situation where there is visible moisture and the temperatures are correct to turn that moisture to ice then that ice will stick to the airframe.

For that snowflake to stick to something which is already frozen would require a portion of that flake to be in liquid form first.

Pace

[M609]

For that snowflake to stick to something which is already frozen would require a portion of that flake to be in liquid form first.


......which it is some of the time.......

One day the airport snowblower can move trough a string of loose snow at 60kph, the next day it can only make 20kph trough a loose string of the same size.

Difference in fluid content? :ok:

[cockney steve]

Difference in fluid content?

NO!.....more probably a difference in the DENSITY of the layer of snow.

As is oft reported by our snowbound services, "it's the wrong type of snow"

by and large, the crystalline tructure of snow is dependent on the speed with which it 's constituent drops are frozen and the size of those drops......so you get extremes from big, soft fluffy flakes , to small granules almost akin to sand.

I would suggest that these factors have a massive effect on snow-blower performance.

Moving partially thawed (WET) snow -AKA SLUSH is a different kettle of fish entirely.

As eni fule kno, if you chuck a snowball at a vertical surface, it will normally stick where it impacts (the rest falls off 'cos the snow is not strong -enough to support the whole lump.)

whether the "sticking" is due to the boundary layer melting with the impact-compression, then refreezing "instantaneously" is for higher minds than mine.......

take a block of butter from the fridge, slap it repeatedly down onto a flat surface......it absorbs the energy and rapidly softens :)


edited for typos and butter experiment.

[scooter boy]

Sleet (freezing rain) is by far the stickiest.

Rain can also cause icing in the right conditions .

Snow tends not to stick.


This whole discussion re how wet the snow is really reflects the difference between sleet and snowflake.

Problem is, you fly through a frontal system with all kinds of convective effects going on and before you know it you have a little frost on the leading edge.
Fly through a shower that is a little sleetier and you will have centimetres of ice accretion on the wing in seconds.

So if it's a small cell and you can see through the other side you're probably safe going through VFR.
If you're crossing a front (i:e the conditions experienced in SE England Sun/Mon) then, you'd better be ready to have some options if the icing gets nasty, and it can get very nasty very fast.

SB

[Pace]

Difference in fluid content?

For those who want to read up on snow :) and I repeat SNOW will not attach to your aircraft as it is already in a frozen state. What do you think happens? is there some sort of glue or honey on the wing leading edges where the snow sticks too?

A Snowflake Primer
... The basic facts about snowflakes and snow crystals ...

Snowflakes and snow crystals
Snowflakes and snow crystals are made of ice, and pretty much nothing more. A snow crystal, as the name implies, is a single crystal of ice. A snowflake is a more general term; it can mean an individual snow crystal, or a few snow crystals stuck together, or large agglomerations of snow crystals that form "puff-balls" that float down from the clouds.

The structure of crystalline ice
The water molecules in an ice crystal form a hexagonal lattice, as shown at right (the two structures show different views of the same crystal). Each red ball represents an oxygen atom, while the grey sticks represent hydrogen atoms. There are two hydrogens for each oxygen, so the chemical formula is H2O. The six-fold symmetry of snow crystals ultimately derives from the six-fold symmetry of the ice crystal lattice.

Snowflakes grow from water vapor
Snowflakes are not frozen raindrops. Sometimes raindrops do freeze as they fall, but this is called sleet. Sleet particles don't have any of the elaborate and symmetrical patterning found in snow crystals. Snow crystals form when water vapor condenses directly into ice, which happens in the clouds. The patterns emerge as the crystals grow.
The simplest snowflakes
The most basic form of a snow crystal is a hexagonal prism, shown in several examples at right. This structure occurs because certain surfaces of the crystal, the facet surfaces, accumulate material very slowly (see Crystal Faceting for more details).
A hexagonal prism includes two hexagonal "basal" faces and six rectangular "prism" faces, as shown in the figure. Note that a hexagonal prism can be plate-like or columnar, depending on which facet surfaces grow most quickly.
When snow crystals are very small, they are mostly in the form of simple hexagonal prisms. But as they grow, branches sprout from the corners to make more complex shapes. Snowflake Branching describes how this happens.

The Morphology Diagram
By growing snow crystals in the laboratory under controlled conditions, one finds that their shapes depend on the temperature and humidity. This behavior is summarized in the "morphology diagram," shown at left, which gives the crystal shape under different conditions. Click on the picture for a closer view.

The morphology diagram tells us a great deal about what kinds of snow crystals form under what conditions. For example, we see that thin plates and stars grow around -2 C (28 F), while columns and slender needles appear near -5 C (23 F). Plates and stars again form near -15 C (5 F), and a combination of plates and columns are made around -30 C (-22 F).
Furthermore, we see from the diagram that snow crystals tend to form simpler shapes when the humidity (supersaturation) is low, while more complex shapes at higher humidities. The most extreme shapes -- long needles around -5C and large, thin plates around -15C -- form when the humidity is especially high.
Why snow crystal shapes change so much with temperature remains something of a scientific mystery. The growth depends on exactly how water vapor molecules are incorporated into the growing ice crystal, and the physics behind this is complex and not well understood. It is the subject of current research in my lab and elsewhere.

The life of a snowflake
The story of a snowflake begins with water vapor in the air. Evaporation from oceans, lakes, and rivers puts water vapor into the air, as does transpiration from plants. Even you, every time you exhale, put water vapor into the air.
When you take a parcel of air and cool it down, at some point the water vapor it holds will begin to condense out. When this happens near the ground, the water may condense as dew on the grass. High above the ground, water vapor condenses onto dust particles in the air. It condenses into countless minute droplets, where each droplet contains at least one dust particle. A cloud is nothing more than a huge collection of these water droplets suspended in the air.
In the winter, snow-forming clouds are still mostly made of liquid water droplets, even when the temperature is below freezing. The water is said to be supercooled, meaning simply that it is cooled below the freezing point. As the clouds gets colder, however, the droplets do start to freeze. This begins happening around -10 C (14 F), but it's a gradual process and the droplets don't all freeze at once.
If a particular droplet freezes, it becomes a small particle of ice surrounded by the remaining liquid water droplets in the cloud. The ice grows as water vapor condenses onto its surface, forming a snowflake in the process. As the ice grows larger, the remaining water droplets slowly evaporate and put more water vapor into the air.
Note what happens to the water -- it evaporates from the water droplets and goes into the air, and it comes out of the air as it condenses on the growing snow crystals. As the snow falls there is a net flow of water from the liquid state (cloud droplets) to the solid state (snowflakes). This rather complicated chain of events is how a cloud freezes.

[Pace]

Scooter Boy :ok:

pace

[Piper.Classique]

Aerotowing a glider off a runway covered in dry snow is fun (for the tug pilot) :E

[Pilot DAR]

It's not quite a flying question, but this sounds like the place to ask about operations in snow, so here's my question:

The news said that the London public transit system was completely shut down because of the snow fall. This was said to include the underground. Does the transit authority not have snowploughs for the underground rails in the tunnels? Or is it that the snow falling in the tunnels is sticking to the trains, and ruining their lift? Oh, I know, the snow is clogging the grilles, so the train engines cannot get enough induction air, and are running too rich!

Pilot DAR

[Mark1234]

Actually there are significant portions of the underground that run -er- overground... not to mention that the uk falls appart with 3 flakes of snow, and the poor drivers probably couldn't get into work...

[Pilot DAR]

not to mention that the uk falls appart with 3 flakes of snow

Yes, I see the problem!

London needs some of those intrepid PPRuNers to go flying, and have the snow stick to their wings, rotors and grilles, instead of falling on London. Such a selfless application of aviation could then result in the Prime Minister announcing to the nation; "Never in history of winter meteorology was so much owed by so many to so few"

[RatherBeFlying]

That's quite a fine description of snowflake formation put up by Pace.

The only thing I would add is that significant heat is given off as water freezes either from liquid or vapor.

Snow showers tend to come out of cumulus clouds as the released heat stirs things up.

Latent Heat of evaporation, fusion, and freezing (http://apollo.lsc.vsc.edu/classes/met130/notes/chapter2/lat_heat2.html)

[Pace]

Pilot Dar

We in the UK have not seen snow before. Millions woke up pulled the curtains and thought they had gone colour blind seeing everything in black and white so many called in sick.

London scientists examined this strange stuff which was lying in the streets.
The London tubes failed to run as the drivers refused to come out of the underground portions of the tube. They had seen people who had changed into snowmen and were scared stiff of coming into contact with the material.

Worse still was the horrors that these people turned to snow now sprouted carrots where their proud noses once lay.

Buses and cars lay abandoned on the streets of London as their drivers realised that the yellow no parking lines were no longer visible and they could get free on street parking.

Traffic wardens were being rounded up by these ecstatic drivers who were seen herding them into groups and stoning them to death with snow balls.

Do not believe the reason the airports closed. The real reason was the UK pilots believed the stuff may stick to their aircraft turning their planes into giant snowballs streaking through the skies never to be seen again. The runways were set aside exclusively for Father Christmas to practice his touch and goes ready for next Christmas.

The UK PrimeMinister was seen pacing up and down the streets of London. he was heard mumbling that the state of the economy was not his doing. It was an act of God as was the snow As he added another 3 billion to our debts :)

Hope that explains everything for you :)

Pace

[Mark1234]

<grin>

I should add I'm an expat londoner, so feel reasonably justified in having a dig..

[Pilot DAR]

Ah, I can thus see the need for a rallying cry to the people....

Let me think.....

"We shall get sand from the beaches, we shall plough the landing grounds, we shall ignore the fields, and spread the sand on the streets, we shall summon more help from the hills; we shall never surrender..."

With that, the indefatigable English sprit will forge on, trudging and driving with purpose through the foreign material on the ground, and forging a new spiritual bond with the colonials to the west....

[bookworm]

My guess is that the really dangerous thing is higher up; snow is often (always?) formed when freezing rain falls into colder air, and you definitely do not want to be flying in freezing rain. One meteorologist told me that snow is always formed from freezing rain but I am no sure about this.

Wrong way round.

Most precipitation starts in the ice phase via the Bergeron process. I don't know enough cloud physics to say that this is always "snow" in a technical sense, but you may as well think of it as snow. (Precipitation can also occur through coalescence of water droplets in clouds whose tops are above freezing temperature, but it's not as common as a base mechanism.)

Usually, the ice phase falls into positive temperatures at lower altitude, and produces rain. If the temperature remains below freezing to (or almost to) the surface, it falls as snow.

Only if an inversion exists is there the possibility of freezing rain (though bear in mind that if you take a cold airframe into rain, you may get clear ice that's just like freezing rain). So the precipitation starts as snow at sub-freezing, melts to rain in the above-freezing layer, and then becomes supercooled droplets in the lower sub-freezing lower down. If the lower sub-freezing layer is deep enough, the droplets might freeze from the outside producing ice pellets.

[BackPacker]

Have you also considered that, statistically speaking, at least one molecule of the precip that fell on London in the last few days has at some point been inhaled by either Aristoteles, Darwin, Vincent van Gogh, Martin Luther King, John F Kennedy, Hitler, Bush, Blair, Brown, Bin Laden or yours truly? Most likely even all of them.

So pick your choice on who to blame.

[bookworm]

has at some point been inhaled by either Aristoteles, Darwin, Vincent van Gogh, Martin Luther King, John F Kennedy, Hitler, Bush, Blair, Brown, Bin Laden ...

but presumably not by Clinton :)

[ShyTorque]

Pace,

You seem convinced that snow cannot stick to an airframe. Ever heard of pack snow?

[Pace]

Pace,

You seem convinced that snow cannot stick to an airframe. Ever heard of pack snow?

ShyTorque YES but what has that got to do with an aircraft in flight? It maybe a problem with an aircraft parked up but ??? explain? :)

Pace

[ShyTorque]

??? explain?

Read for yourself???

Here's one place it's discussed: Aircraft icing (http://www.auf.asn.au/meteorology/section10.html)

And another:
HELICOPTER OPERATIONS IN WINTER (http://www.centralflyingschool.org.uk/Winter/HeloOper.htm)

[Pace]

ShyTorque

The prerequisites for airframe icing are:

The aircraft must be flying through visible supercooled liquid, i.e. cloud, rain or drizzle
The airframe temperature, at the point where the liquid strikes the surface, must be sub-zero.

This is pasted from your example article. I repeat Snow in its pure form will NOT cause icing on an aircraft. Please read the section I posted on the composition and creation of SNOW.

A snow flake is composed of DRY ice and as such cannot cause icing unless it is melted back ino liquid at which point it is no longer snow.

Again read the snippet I highlighted concerning sleet.

Supercooled water droplets or water droplets containing ice particles will cause icing if the temperature is correct for icing but that is NOT SNOW.
It will be the water droplets not the ice paricles contained that will freeze and stick not the ice particles on their own. Without visible moisture NO icing.

For airframe icing to occur there has to be visible moisture and freezing or sub freezing temperatures its as simple as that.
While I agree with the principals of your example article I do not agree with some of their terminology.

I have flown in Snow many times and never once had an icing problem with SNOW in its true sense.

I hope this makes sense ! God this is hard work :ugh:

Pace

[bookworm]

I don't think I believe the assertion that:

"wet mushy snow, which is a mixture of snow crystals and supercooled raindrops, will form pack snow on the aircraft"

Surely "wet mushy snow" occurs when snow partially melts. Doesn't the fact that the snow is melting indicate above-freezing temperatures, in which case the airframe is probably above freezing too?

[ShyTorque]

Pace, why make extra hard work of it by posting twice for emphasis?

I'm not talking about dry white snowflakes building up on the wings, which I think you seem to assume. Flying in wet, sticky snow can result in a build up on any stagnation point. It can block an air intake filter housing or in the case of turbine helicopters, cause a slug of wetness to drop into an intake, causing a sudden flameout. It can also build on the stagnation point of the leading edge of a wing or other aerofoil.

The helicopter type I used to operate / instruct had a twenty minute limit on operations in snow with an in-flight visibility of 400 metres or less. We had external mirrors aimed at the engine intakes for this very reason.

Snow builds on cars whilst they are being driven, too - I'm sure you've noticed. Why should aircraft be different?

[Pace]

ShyTorque rectified the double posting sorry about that.

Snow will block any aperture on the airframe if it cannot pass through or has no where to go. A fine grille could cause that an open engine inlet no because the flakes blow through and melt.

On most clean airframes there will not be any areas which will block their passage.

The problem with a car is that its speed envelope will vary from zero to maybe 100 mph.

In snow it speed will probably vary from zero to 30 mph and be varying between that range.

ie not enough airflow at times to blow the flakes away.

As with any snow accumualtion there is a difference between the surface temperature and sub temperatures of the accumulated snow so accumulated snow will vary.

You can walk on snow where the sub layers have melted refrozen and had fresh accumulations on top.

The car is not a good comparison. If you taxied an aircraft on the ground in heavy snow at varying speeds from zero to 30 mph in heavy snow yes you would get the snow settling on the airframe but not at a constant 120 kts +

Pace

[Bertie Thruster]

But what about an airframe flying at 40 to 60 kts?

[M609]

I have removed blocks of wet snow from both wingroot cabin air intakes on a C172 once, so I know that it builds up there at least.

Now, I was in a big hurry to land just prior, the showers turned to be a bit more intense than i anticipated. (Was just in doing TGL in the circuit)

[Pace]

But what about an airframe flying at 40 to 60 kts?

Bertie

I cannot give you an exact speed where there is enough air passing over an object to stop a snowflake from settling. In a car you may come to a stop at a road junction in which case the flakes will settle. They land on the car. There maybe heat coming from the engine at a standstill allowing the snow to melt and then the liquid to freeze on accelerating.

There is no such thing as sticky snow. That implies some sort of glue or stickyness which allows it to attach to objects.

True snow is dry and frozen so cannot attach to a frozen surface. Only visible moisture combined with freezing temperatures can attach.

Pace

[Pace]

M609
I have removed blocks of wet snow from both wingroot cabin air intakes on a C172 once, so I know that it builds up there at least.

I dont have a problem with that. If the flakes cannot blow through or the inlet is not heating then yes they will block that aperture.

You should not have a problem with engine cooling inlets unless there was some fine mesh grille over the opening.

Pace

[ShyTorque]

Bookworm, supercooled water droplets can exist alongside snowflakes. Does that help your understanding? If not, believe what you will, I wish you luck and hope you safely enjoy your cold weather flying in the future. I'm not going to argue the academics or semantics about whether it's academic still snow now or is it academic ice stuck to my aircraft because I know from other discussions here that written debate often can't change a long time fixed belief derived from reading.

A while ago I took part in similar discussion, about carb icing and the possible effects of the use of partial carb heating, other "experienced" pilots couldn't understand the concept that it might be counterproductive not to use FULL heat. One person in particular hadn't realised that fuel evaporation could cause a temperature drop of 20 Celsius in the venturi and believed it was all down to the Bernoulli effect. He's probably still unconvinced.

During another more recent discussion, at least one "experienced" poster said it wasn't possible for helicopters to suddenly cause a highly localised visibility reduction to the point where IMC conditions existed. Until the moderator posted a video showing exactly what I was talking about. He hadn't experienced those weather conditions himself and posted that it therefore couldn't happen...

My own practical experience tells me that some over-generalisations have been stated, especially where operations close to freezing temperatures are concerned. Colder arctic (drier) temperatures can be less dangerous than than those just above or just below freezing, such as in UK of late.

I joined in this debate because I felt concerned that an inexperienced pilot might read what has been posted and assume that falling snow is of little consequence to his winter flight, other than from a reduction in visibility.

I'm not a met expert, only a pilot of some 32 years professional experience, including military winter operations in weather conditions close to (and sometimes unfortunately in) snow and icing conditions. These days, flying an IFR capable aircraft without an icing clearance, I have to draw on my practical experience to keep it safe all year round, while getting the job done whenever possible. Especially as someone previously told the aircraft owner he was buying an all-weather aircraft. :uhoh:

I hope my input has balanced the debate somewhat, others can decide for themselves.

[Pace]

ShyTorque

This conversation was about snow and whether snow in its true form can stick to an aircraft.

Naturally flying in any conditions where there is visible " moisture" and temperatures conducive to icing in an aircraft which is not Ice capable is asking for trouble, but that advice is valid if there is NO snow.

It is equally dangerous to imply to inexperienced pilots that because its not snowing or sleeting that all is ok.

Snow and sleet are both dramatic visual indications of ice in the sky but the danger is not the formed ice but the moisture that can turn to ice. It is the moisture which is not so visually dramatic which is the silent killer.

For that reason it is important to understand the physics of icing

The answer to "can pure SNOW in its true form which is a dry frozen and complex structure cause an icing problem?" then the Answer is NO.

Can flying in conditions where there is visible moisture and freezing conditions whether snow is present or not cause icing? YES.

Is snow indicative of icing conditions? Maybe Maybe not.

Pace

[Whirlygig]

This conversation was about snow and whether snow in its true form can stick to an aircraft.
The conversation was about snow but you're the only one who is talking about it in it's pure" form.
The answer to "can pure SNOW in its true form which is a dry frozen and complex structure cause an icing problem?" then the Answer is NO. Nobody asked about "pure" snow so you're answering a question that hasn't been asked.

Whilst you are scientifically correct, "pure" snow is not that common so a semantic arguement based on theoretical molecular structure and is no real help or guidance in real life.

It is equally dangerous to imply to inexperienced pilots that because its not snowing or sleeting that all is ok.
Nobody made ny such implication and your use of that corollary is misleading.

but the danger is not the formed ice but the moisture that can turn to ice.
Formed ice not a danger? I hope you don't believe that.

Cheers

Whirls

[bookworm]

Bookworm, supercooled water droplets can exist alongside snowflakes. Does that help your understanding? If not, believe what you will, I wish you luck and hope you safely enjoy your cold weather flying in the future.

"Can exist"? Yes, I think I can accept that. In the same way that supercooled water droplets "can exist" as freezing rain. But in the same way that most rain is not freezing rain, I think most wet snow does not have a significant supercooled liquid component. The only explanation I can come up with for the phenomenon is that the latent heat of melting of the snow cools the accompanying liquid water below freezing.

I would be the first to acknowledge that practical experience trumps simplistic science, and I do not undervalue your input, ShyTorque, here or elsewhere. But I do think that understanding the science of weather can help us manage risk better and keep us safe. Some of that is about understanding why some aspects of weather pose less of a hazard than one might naively expect.

[ShyTorque]

ShyTorque
This conversation was about snow and whether snow in its true form can stick to an aircraft.
Naturally flying in any conditions where there is visible " moisture" and temperatures conducive to icing in an aircraft which is not Ice capable is asking for trouble, but that advice is valid if there is NO snow.
It is equally dangerous to imply to inexperienced pilots that because its not snowing or sleeting that all is ok.


The original poster actually said "snowy stuff" in his question. I saw a danger in over generalisation; which you appeared to do by confining your discussion to "snow in it's true form", (your quote, not the original poster's) which seldom occurs, at least not at the temperatures seen in UK and most of Europe.

This quote didn't help:

Do not believe the reason the airports closed. The real reason was the UK pilots believed the stuff may stick to their aircraft turning their planes into giant snowballs streaking through the skies never to be seen again. The runways were set aside exclusively for Father Christmas to practice his touch and goes ready for next Christmas.


In my view, that implied that you were pouring scorn on any pilot who didn't fly in the worst icing conditions we have had in UK for many years.

[Pace]

Whirly

Formed ice not a danger? I hope you don't believe that.

In the context we are talking about formed ice is NOT a danger and I am not talking about ice forming on your airframe :) We are talking about snow, ice pellets ie hail (Oh yes that would be a danger but not in the context of icing on the wings)

So please enlighten me to how formed ice is a danger to aircraft icing as I would like to know?

Whilst you are scientifically correct, "pure" snow is not that common so a semantic arguement based on theoretical molecular structure and is no real help or guidance in real life.

Not that common! you are joking I hope? i have flown through tons of the stuff a lot at night.

Snow is snow in about 20 types if it melts its no longer snow. Sleet is not snow.

Pace

[ShyTorque]

But I do think that understanding the science of weather can help us manage risk better and keep us safe. Some of that is about understanding why some aspects of weather pose less of a hazard than one might naively expect.

Bookworm, Yes, I can certainly assure you that practical experience of icing soon does away with any naivety or alleged misunderstanding of the science. Perhaps you could enlighten us with further with regard to your own practical experiences of operating in and around icing conditions, or knowing how and when to avoid them?

[Whirlygig]

In the context we are talking aboutPace, you're doing it again; it's a context that only you is talking about, not me.

I am not talking about ice forming on your airframe
How do I know that from your earlier statement which stated that formed ice is not a dnager?
We are talking about snow
Again, you said "formed ice" and now you say "snow". These semantics are not helping anyone.

Formed ice on rotor blades is a danger.

Cheers

Whirls

[Pace]

Whirls okay :)

Snow is formed ice it is a structure of very pretty forms and shapes all created out of dry ice. Melt it and the poor thing collapses into a very unnatractive drop of water :) But hey ho its not the frozen stuff I fear its its the liquid stuff which can freeze.

Pace

[ShyTorque]

Pace, we all know that sarcasm is the lowest form of wit but an attempt to patronise and be sarcastic at the same time doesn't reinforce your argument one bit. As you said early on, you are being over pedantic and by doing so you do not give a practical answer to the poster's original question.

I won't post further here but I've sent the original poster my honest advice with regard to his original question by other means.

[Pace]

Do not believe the reason the airports closed. The real reason was the UK pilots believed the stuff may stick to their aircraft turning their planes into giant snowballs streaking through the skies never to be seen again. The runways were set aside exclusively for Father Christmas to practice his touch and goes ready for next Christmas.

In my view, that implied that you were pouring scorn on any pilot who didn't fly in the worst icing conditions we have had in UK for many years.

Shytorque

That was a humouros reply to an equally humouros question about why does the UK grind to a halt with a liitle bit of snow made by Pilot Dar.

You state that we had the worst icing conditions we have had in the uk for many years? were there warning in the met of severe icing on those days?
Pouring scorn? No but maybe making a point that Snow does not equal icing conditions.
You may have had years of experience flying in all weather but so have I.

The worst icing experiences I have had have never involved Snow and in Snow I have never experienced icing.

I would not encourage anyone to takeoff in a light aircraft without experience and full deice/anti ice if visible moisture and icing temperatures are present close to the ground whether in rain, sleet, or snow and I resent your implication.

Pace

[drambuster]

If you recall, this thread started with LateFinals "looking out of the window" at the snow fall earlier this week and speculating about whether it would be OK to fly in those conditions. The answer, according to Flying magazine in the US, is a resounding 'yes' (assuming you're OK with panel flying and it's not a howling storm).

Reading the entire thread again I think that the experience of those from Canada (eg PilotDAR) and similar places that live with the stuff half the year is that they are fine about flying in it . . . . which was the original question. Obviously if there is a propensity for icing (wet slushy stuff) then that is a different question that did not represent the prevailing conditions across GB at the start of the week.

Therefore my vote is that Pace has won the argument hands down ( :D ) and I can't wait to get up there and mix it with the next snow flurry. If I don't make it back then groveling apologies to Parsnip, et al, as it clearly was safer just to have stayed tucked up in bed !

Drambuster

[Pace]

Drambuster

Thats where I bow out :) off to build a few snowmen and contemplate the structure of the snowflake, great stuff to ski on :)

Pace

[ShyTorque]

Pace, by your very own argument that's impossible because pure snow won't stick to anything. :D

[Pace]

shyTorque

Dont show your ignorance

Pace

[ShyTorque]

Shytorque
That was a humouros reply to an equally humouros question

Not so much evidence of a sense of humour now.... :rolleyes:

[Pace]

ShyTorque

Ok, we beg to differ! friends? :)

Pace

[gasax]

With respect, the Canadian experience is not terribly relevant to conditions in the UK.

I would firmly support Pace's snow does not stick to anything line if I were flying out of somewhere with -20 deg C. At those temperatures snow is squeaky and acts just as Pace's text book description.

However looking out the window here is another matter. This morning when being warned of an exceptionally cold night and slippery roads it was -2.5 deg C air temp. The water on the roads was liquid (no salt applied up here!)

These are the conditions where you see snow and yes Pace it builds up on airframes.

[LateFinals]

Having posed the original question about flying in snow and now read and digested the range of responses I feel that for the majority of pilots and the GA planes they fly, the white stuff is best avoided at all costs.


LF

[Pace]

Gasax

The reason I have hammered away about this is not as some seem to get the impression that I want to score points but so we can all hammer out a true understanding about snow.
I have made mistakes in other threads and am happy to be corrected and would be equally happy to be corrected in this one. The important thing is that a true picture is arrived at through any of these threads.

Some posters refer to sticking as if the snow sticks like glue. No dry ice will stick to a frozen surface. If you took a frozen Ice cube from your fridge and tried to attach it to a frozen suface it would not stay. Warm part of that icecube so a portion on the suface becomes wet and recontact that against a frozen surface and it will refreeze attaching itself and the cube to the surface.

The difference with snow is that to be snow the flake has to have a structure of tiny very delicate ice crystals. The nature of snow is that there is no moisture content. The moisture has evaporated off in its development.

Snow falls as individual flakes not en masse and is very easy in loosing its structure if warmed.

Sleet is a very different animal. Snow can develop into sleet but is no longer snow. Sleet can have a centre of ice surrounded by liquid. Sleet is an icing danger as for any icing there HAS to be visible moisture and the correct temperatures for icing to form on the airframe.

My worst icing experiences and I have had a few have involved rain, cb activity etc. On one occasion was flying a business jet from Prague to Istanbul. We took off in rain in solid cloud and didnt top the cloud until FL200.
The ice build up was fast until we got into colder air in the climb. When we could see tiny ice crystals replacing the rain the icing stopped.

Snow has a large visual impact of suggesting COLD AND ICE but it is not the cold and ice which is your threat it is the far less visually threatening water or moisture which is if the temperatures are freezing or below.

So it is no worse flying in snow when the ground is pure white than it is taking off when the fields are green in rain.
Both require caution but snow is not your threat and dont confuse sleet with snow they are not the same.

Pace

[Pilot DAR]

When we could see tiny ice crystals replacing the rain the icing stopped.


This is a key concept, and also my observation a number of times. Once, and only once, while flying a non-deiced aircraft, and collecting ice, going down or back were just not safe options, going up was. I'm not recommending it, but that time it worked. We made it to colder air, and stopped accumulating ice. Over several hours, that ice which we had accumulated, left by sublimation. I've always figured that is how the word sublime originated, the pleasing feeling a pilot has when the ice leaves the plane on it's own!

We do also get the odd storm of wet slush, and worse falling from the sky here, and anyone would be unwise to attempt to fly most aircraft types in that, but we distinguish it from snow by calling it all sorts of other names, which imply liquid water is falling.

Twice while flying in snow, it has suddenly turned to freezing rain (air temperature locally rose quite quickly), and you could see it happening. The windshield ices over right away, and the engine will suddenly stop due to air filter icing over. Alternate air, and an immediate 180 are the only wise solution - but I was not flying in "snow" any more! Lesson learned, if you're flying in snow, into warmer air while still in percipitation, watch out!

Any pilot who chooses to not fly in precipitation is to be commended for using judgement appropriate to his or her experience or comfort level. That does not mean that such flying cannot be safely accomplished by others.

We have to be careful not to use the forum as a means of instructing or directing pilots to fly in a way which would be unsafe for that individual, but we also are being fair if we cautiously say "yes, it is safely possible, if you are properly trained, experienced or mentored.

Flying in snow can be safely accomplished, and with a few exceptions (like hovering some helicopters) for extended periods of time. While doing it, you may be closer to operating in unsafe conditions, should the temperature change. Not everyone should try it, just as not everyone should attempt to land in a crosswind.

Pilot DAR

[Droopystop]

I think this thread reveals what is really great about the Private Flying forum and also illustrates one of its drawbacks. Of all the forums, I suspect this one has the most diverse population of users. From un powered flight through micro lights, spam cans to private and corporate jets and even the occasional heavy metal pilot, not to mention wayward rotorheads like me.

In this thread we have the theory of "snow" and how it doesn't stick to PACE machinery whereas it does to Shy Torques and my own. I agree that snow in its purest form won't stick to a cold airframe, but something that looks suspiciously like snow will stick to my airframe. Quite how I am not sure, but flying through a "snow" shower can bring it about. (PACE - note the quote marks; there's snow and "snow")

In short a question like this will yield an outpouring of wisdom freely given by a bunch of anonymous experts - experts in their own corner of aviation. It is all to easy to forget that we either don't know what corner of aviation the original poster is coming from or that we don't apply our knowledge to the appropriate corner (and there are many on this forum). Perhaps we should all make it a little clearer what experience our advice is based on and what corner of the forum we are coming from.

What I would say on the original subject is if you go flying in snowy weather wear some gloves and make sure your destination/alternates/home base won't close behind you.

[Pace]

Droopystop

Firstly as with Pilot Dar who is an experienced Pilot i would not recommend anyone flying out of their or their aircrafts ability anymore than as he said I would not recommend anyone flying a crosswind landing beyond their abilities.

As for my own experience i hold an ATP, current Citation rating and have about 4000 hrs. 2000 plus are in multi engines pistons. I fly as a Citation Captain and have also flown a number of ferries around the world.

I used the term Snow in its true form. Infact there is not such a thing its either Snow or not Snow. Snow is a specific structure of very fine Ice particles. One of the attributes of Snow is that there is no moisture content. That was evaporated in its formation.

Any airframe icing requires visible moisture and temperatures conductive to icing ie at or below freezing.

So Snow and airframe icing do not go. Sleet which is what I feel most are confusing themselves with is not snow. Sleet is mixed ice and water which is a threat to icing.

I have gone through all my posts in this thread. I am very happy for anyone to pick any of them to pieces but based on fact and not statements like "you are wrong" without any scientific reasoning why?

I too would love to know the experience and qualifications of some here who make their statements. I am happy for my arguements to be pulled to pieces on an informed and scientific basis and would be the first to say "sorry I was wrong".

I personally have no worries flying in snow. Sleet yes! or any situation where visible moisture and freezing conditions exist.
Whether there are cold temperatures conducive to icing but with green fields and rain or white fields and snow makes no difference. It is the visible moisture to ice up my airframe in either case which bothers me and NOT snow.

Pace

[ShyTorque]

Bertie Thruster asked about aircraft operating at low speed; I know exactly why he asked. Aircraft limitations are type specific and the same in-flight conditions can affect different aircraft in different ways. As I previously posted, one aircraft I previously flew and instructed on (over 2500 hours on that type) had a limitation of 20 minutes in snow conditions because snow could build up on the airframe between the engine intakes, slide sideways and flame out an engine. The aircraft was later fitted with external mirrors so the pilot could check for a snow build-up.

Here's an extract of an accident report involving snow build up on another aircraft type, the Hughes 369D, it occurred in Yukon, Canada. Note the additional information given by the manufacturer about operation in snow, as well as advice on icing conditions. I have emboldened some relevant parts for the hard of hearing.


The helicopter manufacturer's Flight Manual, "Normal Procedures" (Section IV), 4-6 "Actions Before Take-off," states the following requirement: "Use engine anti-icing when OAT is below 5 degrees Celsius (41 degrees Fahrenheit) and visible moisture is present." The engine anti-ice system prevents ice buildup on the engine inlet support struts which could break off and damage the compressor blades.

The Flight Manual, Limitations, (Section II), Chapter 2.3, Flight Restrictions, states the following:

Flight operation is permitted in falling or blowing snow only if the Automatic Engine Reignition Kit and Engine Failure Warning System are installed and operable. Whenever the helicopter has been parked outside or has been in flight during falling snow, determine that the engine inlet area and all helicopter exterior surfaces are completely free of accumulated ice and snow. In addition, open the plenum chamber door and visually determine that the inlet screen or particle separator (if installed) have not become clogged with ice and snow. This inspection and removal of ice and snow shall be accomplished prior to the next flight.

Discussions with other operators of McDonnell-Douglas 369D helicopters indicate that they had also experienced numerous losses of engine power (flame-outs) in falling snow, and had installed optional engine air deflector kits, which eliminated the problem. The kit consists of a plate that covers the normal air intake on the "doghouse" and prevents snow from directly entering the particle separator. Installation of this kit is currently not mandatory.

On 30 September 1982, the Allison Engine Company issued a Commercial Service Letter warning of engine flame-outs due to snow or ice ingestion on the Allison 250 series engines. The letter states:

Owners, operators and pilots are warned that helicopters using this engine in falling or blowing snow, or icing conditions, require special equipment. Snow or ice can build up on aircraft parts, inlet ducts or plenum chambers and break loose in "slugs". Slugs of snow or ice entering the compressor of these engines can cause flame-out. Helicopter manufacturers use different approaches to prevent slugs of snow or ice from being ingested by the engine. Some of these devices include special particle separators, reverse inlet scoops, and various types of inlet screens. Additionally, some helicopters utilize auto-reignition kits to relight the engine in the event that a flame-out occurs. It is the responsibility of the owner, operator and pilot to determine that the helicopter is properly equipped and the devices are in proper working order for operation in conditions where snow and ice can build up on the aircraft. It is also very important to inspect the engine inlet area on the pre-flight check when the aircraft has been exposed to an ice, snow, or sleet storm. Accumulations of ice and/or snow can collect in remote areas of the engine inlet air flow path. Removal of these accumulations is necessary, especially downstream of the protective devices, to prevent a possible flame-out caused by the break-off of these accumulations during flight

Top of Page Analysis

The information gathered indicates that the pilot experienced a flame-out and an automatic relight while climbing after lift-off. This would have caused a loss of main rotor rpm, and would have resulted in the cyclic control response problem reported by the pilot. Although the engine compressor contamination observed could result in decreased power output, it would not be expected to cause a flame-out. The most likely cause of engine flame-out in this occurrence would be the sudden dislodging of an accumulation of snow in the air intake plenum, which is consistent with the experiences of other operators of this model helicopter. The successful elimination of snow-induced flame-outs on other similar helicopters following installation of an air deflector kit, indicates that the installation of such a kit on this aircraft probably would have prevented the occurrence.

[Pace]

ShyTorque

Sorry I am not a helicopter pilot and thought we were taling about light GA aircraft fixed wing not helicopters?

Maybe you should post this in the helicopter section as I dont see the relevance to fixed wing? Explain that relevance if you can?

Pace

[ShyTorque]

Pace, The original poster did not say he flew fixed wing.

You would prefer me to move this because it conflicts with your beliefs and statements about aircraft operations in snow? No thanks, I'll leave it here. It's as relevent to light fixed wing ops as your own quotes from your experience in a Citation.

Snow doesn't know if the airframe it collects on belongs to a helicopter or a light aircraft.

[Pace]

Shytorque

There is a massive difference as there is to my car parked overnight in heavy snowfalls or stopping at a junctions in heavy snow or even a fixed wing left out in snow or taxying at 5 kts in snow.

Maybe 3 feet of snow on your house might give a clue!! think about it.

Pace

[Whirlygig]

Pace, Just wondering if there is anything anyone could say that might make you think that your opinions are just that, opinion and not concrete fact? If there is, what qualifications and experience should that person have? And if not, why not just bow out gracefully knowing that you are infallable? :E

Cheers

Whirls

[ShyTorque]

Pace, you are missing the point of that accident report and the manufacturer's advice therein and also ignoring what others have written. It's not a problem confined to very low speed ops. The helicopter type I flew with the problem of snow build up on the intakes cruised at 140 kts, not 5 mph. The 20 minute limitation in falling snow covered the full flight envelope.

Irrespective of aircraft type, fixed wing or rotary, an area acting as an airflow stagnation point can collect snow in flight. Your Citation is obviously less likely to collect snow than a light fixed wing or a helicopter because of its design - it was deliberately designed to have few stagnation points. An important stagnation point on a light fixed wing is the leading edge of the relatively blunt wing. Another is the face of the engine air intake filter box fitted to some light aircraft. Whether or not the accumulated snow still looks like it belongs on a Christmas card scene or a snowball stuck to a wall is, for practical and flight safety purposes, unimportant.

I see little point in continuing the debate further. We have different views borne out of our different training and personal experiences. (Seeing as you asked, apart from previous gliding and light aircraft PPL training my first 18 flying years of productive flying were military; the latter 15 years mainly civilian, with a bit of paramilitary stuff in between. I hold fixed wing and rotary pilot instructor qualifications).

One thing that (hopefully) everyone agrees on is that winter operations do need some extra thought. Hopefully, inexperienced pilots unsure about this subject will read all of the views here, do their own research, especially by checking out their aircraft manufacturer's advice on winter ops and come to the correct conclusion.

I'm out, I promised someone.

[Pilot DAR]

Of course, if an aircraft type limits operation in snow, or requires specific equipment or configuration for flight in snow, or cold in general, such limitations or requirements must be followed.

Every airplane I have flown makes a statement with respect to flight into icing conditions. The only aircraft I have ever flown which make a reference to operations in snow are helicopters (MD500 & B206), and to my understanding, the concern seems to be flameout of turbine engines, as opposed to accumulation on the airframe/lifting surfaces affecting flying qualities. There are Flight Manual statements about the MD500 operations in snow, and there are similar statements in the B206 Flight Manual. There are no such statements in the SW300 Flight Manual with reference to snow that I can find (None in Limitations section for sure). The SW300 has many similarities to the MD500 from a aerodynamics and lifting surfaces point of view. I presume that this fact highlights the difference in snow sensitivity, as the SW300 has a piston engine.

Other than the preceding, none of the three mentioned helicopter flight manuals, or any airplane Flight Manual I have ever read refers limitations or warnings for flight in falling snow.

So, we have definite reference to flight in icing conditions, but no reference to operations in snow. That places a huge responsibility upon the pilot to soley determine whether the proposed operation will be in ice, or snow.

If the pilot makes the determination that the operation will be in snow, (helicopter flameout considerations acknowledged), that pilot is free to fly without limitation imposed by the aircraft.

If, on the other hand, the pilot determines that the proposed operation would be in icing conditions, that pilot would be bound by icing limitations, which in the case of many smaller aircraft would mean no flight.

We have agreed here that snow is a type of ice, so a pilot would be free to make the interpretation that flight in snow is flight in ice, and not go. Incidentally, the Canadian regulation do not define "snow" or "ice", so it would be up to the pilot to defend either way.

I can therefore, and with some confidence, assume the entirely self appointed role as arbitrator, and find that both Pace and ShyTorque are indeed correct. A pilot can say snow is ice, ice is limited, and so I'm not flying, and be correct. Or, A pilot can say snow is snow, and it is not limited (other than as mentioned), and I'm going flying, and be correct.

Any pilot who flies in snow, is operating in a higher risk environment - a little, or a lot, it depends on many factors. The pilot is responsible for managing risk, and getting it right.

I caution all readers here, that flight in accordance with the limitations for the aircraft, and in falling snow, is safely possible (unless specifically stated against in the limitations section of the Flight Manual), but may exceed one's skill. Use caution.

Pilot DAR; 33 years and 5000 hours of Canadian year 'round flying, PPL in fixed and rotor wing aircraft, including multi and float/flying boat/amphibian, straight and wheel ski flying, in and on the snow.

[Pace]

ShyTorque

This is one of my earlier postings


Snow building up in/on the induction intakes/filters can have you reaching for hot/alternate air. The Partenavia and Apache are 2 types I've had this issue with.

Granite City Flyer

I almost posted this exception but decided not too. Yes if the snow has nowhere to go ie it hits a flat surface like a grille and doesnt pass through there is a danger that it will block the inlet.

Most aircraft dont have that sort of setup but ones which have a grill over something like an engine intake could block with snow if its unheated. The Partenavia did come to mind but that aircraft doesnt have a good reputation in any icing not just snow.

Pace

The fact is that this is not going anywhere fast and is becoming pointless and personal so its better we beg to differ and leave it and no hard feelings :)

Pace

[[email protected]]

Having just found this thread from another one it has been an interesting read but mostly ignored the original posters question.

He was not talking about Pace's pure snow, he was talking about the stuff we had in UK which, according to all the met reports and forecasts I read was mostly RASN - mixed rain and snow which can (even according to Pace's theories) adhere to the airframe because there is visible moisture.

So for the private pilots out there in UK - do not believe you can go flying in snow (the stuff we get here) and not expect to encounter icing conditions.

One assertion of Pace's which I do think is flawed is that only liquid will freeze - water vapour can sublimate straight to ice as hoar frost or, in fact, in the formation of snow.

I think the point was made to emphasise that ice must melt first before it can re-freeze onto an airframe so yes, a snowflake must melt before it becomes an icing risk but that is what RASN is all about.

Anyway it's nearly Summer:ok:

[bookworm]

He was not talking about Pace's pure snow, he was talking about the stuff we had in UK which, according to all the met reports and forecasts I read was mostly RASN - mixed rain and snow which can (even according to Pace's theories) adhere to the airframe because there is visible moisture.

I think you're missing the point. For ice to adhere to the airframe, you need an airframe that is at a temperature below freezing, otherwise the ice just melts off very shortly after it adheres by heat transfer from the airframe. Generally, the airframe will only be below freezing if the air temperature is below freezing. And if the air temperature is below freezing, you'll get snow, not sleet (RASN, in the UK sense of "sleet").

So why might there be liquid precip but the airframe still be below freezing? One possibility is an inversion, where the precip has passed through an above-freezing layer before falling into colder air again. But that will be freezing rain or ice pellets, not sleet. Another possibility is that the airframe is still cold, having come quickly from a colder environment with e.g. wings full of cold fuel that take a while to warm up to ambient. But again that's not an issue about snow, as the icing that you get in such conditions is likely to be as bad if not worse if the precip type is rain rather than snow.

[Droopystop]

Generally, the airframe will only be below freezing if the air temperature is below freezing. And if the air temperature is below freezing, you'll get snow, not sleet (RASN, in the UK sense of "sleet").

I wish I had kept the METARS but across northern Scotland last week, there was the scenario of SN and +ve air being reported simultaneously.

It is interesting that there are two very experienced IFR helicopter pilots who question the wisdom of discarding snow as a potential form of icing. I agree that the formal theory about snow means it won't stick. But in this country whilst we get SN forecast there is a risk it is not really SN, simply because it doesn't really get properly cold in the UK (unless you live in Braemar).

As a helicopter pilot myself with a similar number of hours to PACE, all of which are below 5000' and 150kts I have seen what looks like snow stick. In the context of this forum and the original post, I would say that SN on a UK TAF/METAR doesn't necessarily mean icing, but nor does it mean icing won't happen.

Whilst it may seem that helicopters are snow magnets, we probably have more in common with the Private fleet than it would first seem - similar speeds and operating altitudes.

[[email protected]]

Bookworm - but you don't have an airframe temperature gauge and the metal skin of your aircraft in a 100 kt wind (cruise) is likely to be lower than the OAT if you have melted snow evaporating from it. Add to that the variations in temp that will naturally occur in and around the base of convective cloud and you cannot in any way be sure that just because you see snow there is no risk of icing.

[bookworm]

Bookworm - but you don't have an airframe temperature gauge and the metal skin of your aircraft in a 100 kt wind (cruise) is likely to be lower than the OAT if you have melted snow evaporating from it.

Well there's a mechanism, at least. I'm not convinced that the latent heat of evaporation is an issue -- otherwise we'd see the same cooling effect in rain, and I don't think that's observed. There's also the latent heat of fusion of the snow as it melts that can take some heat away from the airframe.

Add to that the variations in temp that will naturally occur in and around the base of convective cloud and you cannot in any way be sure that just because you see snow there is no risk of icing.

And I would agree with that. But the point is that the circumstances have to be quite special for SN or RASN to pose a significant icing risk. The mere presence of RASN doesn't have to set off alarm bells like FZRA should.

[bookworm]

I wish I had kept the METARS but across northern Scotland last week, there was the scenario of SN and +ve air being reported simultaneously.

Isn't the reverse what you want to demonstrate your point -- that RASN can occur in negative temperatures? I don't think there's much doubt that SN can occur when the OAT is above zero -- it just hasn't had time to melt yet.

Let me help with the stats. Here are the northern Europe (codes beginning with E) METARs containing sleet for the last 30 days.


wx | temperature | count
----------------+-------------+-------
-RASN | -2 | 3
-RASN | -1 | 8
-RASN | 0 | 238
-RASN | 1 | 645
-RASN | 2 | 346
-RASN | 3 | 107
-RASN | 4 | 21
-RASN | 5 | 1
-RASN | 6 | 3



wx | temperature | count
----------------+-------------+-------
RASN | -1 | 6
RASN | 0 | 35
RASN | 1 | 116
RASN | 2 | 87
RASN | 3 | 24
RASN | 4 | 6


The vast majority of RASN occur in positive temperatures. Compare that with FZRA


wx | temperature | count
----------------+-------------+-------
-FZRA | -10 | 2
-FZRA | -9 | 3
-FZRA | -8 | 12
-FZRA | -7 | 11
-FZRA | -6 | 16
-FZRA | -5 | 8
-FZRA | -4 | 15
-FZRA | -3 | 11
-FZRA | -2 | 14
-FZRA | -1 | 38
-FZRA | -0 | 38
-FZRA | 1 | 1
-FZRA | 2 | 1


Is it worth paying attention to icing when there's RASN around? You bet it is. But most of the time, snow melting into sleet is not a problem.

[[email protected]]

Bookworm - you run the risk of arguing the same sort of semantics as Pace did about 'pure snow'.

If you want to go flying in the snow, crack on but it comes with several health warnings:

Poor visibility and the possibility of whiteout (can't distinguish land from cloud). This makes trying to continue VFR much more risky and if you have no TCAS or radar service makes deconfliction with other traffic far more difficult.

Possible icing in the RASN.

A high probability of icing in the cloud that is producing the snow/sleet, greatly reducing your IFR options. Once you are in it your airframe will be below zero amongst a mixture of supercooled droplets and snow.

All the ground based issues like slippery taxiways, runways, banks of slush and snow etc.

If you want to risk all that just to fly in falling snow...................

[bookworm]

This makes trying to continue VFR much more risky

Quite why anyone would attempt to fly VFR in snow is beyond me! That, and the ground risks you cite, are not at issue here.

A high probability of icing in the cloud that is producing the snow/sleet, greatly reducing your IFR options. Once you are in it your airframe will be below zero amongst a mixture of supercooled droplets and snow.

No, that's the whole point. A lower probability of icing in the cloud that is producing the snow/sleet, because the presence of snow is an indicator of glaciation and the probable absence of supercooled water. If you have a choice between a cloud in which it's snowing, and a cloud at the same temperature in which it's yet not snowing, pick the one that's snowing! And while your airframe may be below zero, it may not be even in dry snow, and it unlikely to be below zero in snow that has already started to melt to make RASN.

[ShyTorque]

If you have a choice between a cloud in which it's snowing, and a cloud at the same temperature in which it's yet not snowing, pick the one that's snowing! And while your airframe may be below zero, it may not be even in dry snow, and it unlikely to be below zero in snow that has already started to melt to make RASN.

Bookworm, in view of the fact that you won't know the temperature of a cloud until you're in it, how do you know which is the "best" cloud to fly in?

Before you answer the question, perhaps you would kindly outline your practical experience of winter operations and snow flying and what formal /paper qualifications you have to make such a statement?

[bookworm]

Before you answer the question, perhaps you would kindly outline your practical experience of winter operations and snow flying and what formal /paper qualifications you have to make such a statement?

Woof (http://en.wikipedia.org/wiki/On_the_Internet,_nobody_knows_you're_a_dog). Perhaps my only paper qualifications and practical experience of winter operations are that I fetch the paper for my master in the snow? Would that make you less likely to believe me than if I claimed to have a PhD in physics and fly a booted light-twin around throughout the year? Should it? If you don't believe what I write about icing, why don't you do your own research?

in view of the fact that you won't know the temperature of a cloud until you're in it, how do you know which is the "best" cloud to fly in?

You're twisting the way I chose to express that. The simple point is that the higher icing potential comes from clouds that have high supercooled water content before glaciation, not the ones that are already glaciated and shedding snow at high rate.

There are no certainties when it comes to icing, and any flight in temperatures around freezing is going to have to pay significant attention to conditions. I've not, at any point in this discussion, doubted your practical observations that snow can pose a hazard, particularly to your helicopter. But, perhaps based on the limitations that your flight manual imposes, you seem to be extrapolating to overemphasise the effect of snow on other aircraft. There are other weather phenomena to be more concerned about.

[[email protected]]

Bookworm No, that's the whole point. A lower probability of icing in the cloud that is producing the snow/sleet, because the presence of snow is an indicator of glaciation and the probable absence of supercooled water.

The weakness in your argument is the use of the word probable here - the fact is that to produce snow in the first place you must have supercooled droplets so that the water can evaporate from the droplets and form ice crystals on the freezing nuclei (the Bergeron-Findeisen process).
So, since both will exist in varying amounts depending on the conditions you cannot say with any certainty that the snow cloud will be a lesser icing hazard than the no-snow cloud.

The simple point is that the higher icing potential comes from clouds that have high supercooled water content before glaciation, not the ones that are already glaciated and shedding snow at high rate.
again - you talk about differences in potential which is probaby true but is not the hard and fast 'snowing therefore no icing' rule that you advocate.

And then your capitulation There are no certainties when it comes to icing, and any flight in temperatures around freezing is going to have to pay significant attention to conditions. which is what Shy and myself have been trying to get through and why we dislike ridiculous simplifications llike 'it's snowing so there is no risk of icing' which may influence the less experienced on this forum.

[bookworm]

but is not the hard and fast 'snowing therefore no icing' rule that you advocate

And if you read what I've actually written, rather than what you'd like me to have written, you'll see that I've not suggested anything of the sort.

I entered this debate because I objected to an assertion in a cited article that "wet mushy snow" necessarily contains supercooled water. Most of the time RASN does not: it's simply snow that has melted. We seem to be agreed that encountering liquid water precip, whether pure RA or RASN, with an airframe temperature below freezing, has a significant potential for icing.

Reading what you've actually written, I'm probably guilty of similarly misinterpreting you too in what I made of the following:

I think the point was made to emphasise that ice must melt first before it can re-freeze onto an airframe so yes, a snowflake must melt before it becomes an icing risk but that is what RASN is all about.

That RASN is "all about melting" is fair enough. That it's "all about re-freezing" (because it contains supercooled water) is not. I think you simply meant the former, didn't you? In the words that I previously quoted from you, you wrote "can ... adhere to the airframe" not "will". That's perfectly fair.

Finally...

The weakness in your argument is the use of the word probable here

The weakness in my argument is really in my use of "absence". Can we agree that glaciated cloud has a significantly lower supercooled water content than before glaciation?

[Pace]

Crab

Just to clear up a few points i think there is confusion as to what snow is what sleet is and what rain is? Snow is NOT sleet but a specific structure of dry ice particles which contain NO moisture. the particles are so fine that any warming converts those tiny structures into water and ice but that is NO longer snow.

You may see what appears to resemble snow to the pilot but it is likely to be sleet.

Yes if there is a mixture of rain ie visible moisture and snow flakes the rain can form ice but that is the case regardless of the snow.

Dont really want to start this one up again but if anyone can explain the science of snow forming ice please feel free :)

Pace

[Captain Smithy]

This has been an informative discussion which I have followed with interest; perhaps one of the better uses of PPRuNE.

Personally though, after my own experience mentioned earlier, I don't fancy flying in SN again, unless I was IFR in a de-iced machine; even though it was accidental it was a little foolish attempting VFR through SHSN.

P.S. Thanks for the Wiki link earlier, bookworm. I got a bit of a laugh at that.

Smithy

[ShyTorque]

Bookworm,

Please don't jump so strongly to the defence; I noted that your profile doesn't even say if you fly or not and I think it is important to know from which corner folk are arguing from.

I have already done my own research, some years ago and every winter. I've been required to operate in European winters since 1977. The aircraft I've flown most have had no icing clearance or de-icing equipment fitted. They have also, with one exception, been unpressurised and therefore unable to climb above snow or icing cloud. My job has been therefore "in it" or close to it.

A presentation I was asked to give on aircraft icing problems in the mid 1980s was purloined and used by the RAF for some years afterwards, most particularly by 33 (AMF) helicopter squadron, who operated in Norway in the winter. The brief's probably been replaced since Powerpoint etc came along but it might still be lurking in a box somewhere at RAF Odiham.

Although I no longer consider myself FW current I do have FW experience, light SEP and single jet, btw (hence my profile saying "QFI" as well as "QHI". I also hold a CPLA.

Before I bow out of this discussion, I repeat my sole purpose on this thread, which is to put out my own advice that generalisations, with regard to aircraft operating in falling snow and cold cloud conditions are best avoided.

Each manufacturer who wishes to obtain an icing clearance for a particular aircraft is required to test fly the aircraft and prove that it is safe to do so. There is NO "one size fits all" solution to safe operations in winter conditions.

[[email protected]]

Pace - just for you I have kept it simple:)

Bergeron Process - Geography For Kids - By KidsGeo.com (http://www.kidsgeo.com/geography-for-kids/0112-bergeron-process.php)

But if you google 'bergeron process' you will find plenty of answers - wikipedia has enough science for you I suspect.

You will see that, as I have indicated in previous posts, supercooled droplets (of varying sizes and formed on the condensation nuclei) co-exist with ice crystals (formed on the freezing nuclei) and the water evaporates making the ice crystals grow (into snow).

In the UK, sleet (referred to as RASN) is snow that has melted on its descent to Earth and accompanied by snow that has yet to melt. In the US, sleet is snow that has melted and re-frozen into solid, non crystalline particles.

Hope this helps.

[Pace]

Crab

have reposted this for you especially note the comments re sleet.

Pace

Quote:
A Snowflake Primer
... The basic facts about snowflakes and snow crystals ...

Snowflakes and snow crystals
Snowflakes and snow crystals are made of ice, and pretty much nothing more. A snow crystal, as the name implies, is a single crystal of ice. A snowflake is a more general term; it can mean an individual snow crystal, or a few snow crystals stuck together, or large agglomerations of snow crystals that form "puff-balls" that float down from the clouds.

The structure of crystalline ice
The water molecules in an ice crystal form a hexagonal lattice, as shown at right (the two structures show different views of the same crystal). Each red ball represents an oxygen atom, while the grey sticks represent hydrogen atoms. There are two hydrogens for each oxygen, so the chemical formula is H2O. The six-fold symmetry of snow crystals ultimately derives from the six-fold symmetry of the ice crystal lattice.


Quote:
Snowflakes grow from water vapor
Snowflakes are not frozen raindrops. Sometimes raindrops do freeze as they fall, but this is called sleet. Sleet particles don't have any of the elaborate and symmetrical patterning found in snow crystals. Snow crystals form when water vapor condenses directly into ice, which happens in the clouds. The patterns emerge as the crystals grow.
The simplest snowflakes
The most basic form of a snow crystal is a hexagonal prism, shown in several examples at right. This structure occurs because certain surfaces of the crystal, the facet surfaces, accumulate material very slowly (see Crystal Faceting for more details).
A hexagonal prism includes two hexagonal "basal" faces and six rectangular "prism" faces, as shown in the figure. Note that a hexagonal prism can be plate-like or columnar, depending on which facet surfaces grow most quickly.
When snow crystals are very small, they are mostly in the form of simple hexagonal prisms. But as they grow, branches sprout from the corners to make more complex shapes. Snowflake Branching describes how this happens.

The Morphology Diagram
By growing snow crystals in the laboratory under controlled conditions, one finds that their shapes depend on the temperature and humidity. This behavior is summarized in the "morphology diagram," shown at left, which gives the crystal shape under different conditions. Click on the picture for a closer view.

The morphology diagram tells us a great deal about what kinds of snow crystals form under what conditions. For example, we see that thin plates and stars grow around -2 C (28 F), while columns and slender needles appear near -5 C (23 F). Plates and stars again form near -15 C (5 F), and a combination of plates and columns are made around -30 C (-22 F).
Furthermore, we see from the diagram that snow crystals tend to form simpler shapes when the humidity (supersaturation) is low, while more complex shapes at higher humidities. The most extreme shapes -- long needles around -5C and large, thin plates around -15C -- form when the humidity is especially high.
Why snow crystal shapes change so much with temperature remains something of a scientific mystery. The growth depends on exactly how water vapor molecules are incorporated into the growing ice crystal, and the physics behind this is complex and not well understood. It is the subject of current research in my lab and elsewhere.

The life of a snowflake
The story of a snowflake begins with water vapor in the air. Evaporation from oceans, lakes, and rivers puts water vapor into the air, as does transpiration from plants. Even you, every time you exhale, put water vapor into the air.
When you take a parcel of air and cool it down, at some point the water vapor it holds will begin to condense out. When this happens near the ground, the water may condense as dew on the grass. High above the ground, water vapor condenses onto dust particles in the air. It condenses into countless minute droplets, where each droplet contains at least one dust particle. A cloud is nothing more than a huge collection of these water droplets suspended in the air.
In the winter, snow-forming clouds are still mostly made of liquid water droplets, even when the temperature is below freezing. The water is said to be supercooled, meaning simply that it is cooled below the freezing point. As the clouds gets colder, however, the droplets do start to freeze. This begins happening around -10 C (14 F), but it's a gradual process and the droplets don't all freeze at once.
If a particular droplet freezes, it becomes a small particle of ice surrounded by the remaining liquid water droplets in the cloud. The ice grows as water vapor condenses onto its surface, forming a snowflake in the process. As the ice grows larger, the remaining water droplets slowly evaporate and put more water vapor into the air.
Note what happens to the water -- it evaporates from the water droplets and goes into the air, and it comes out of the air as it condenses on the growing snow crystals. As the snow falls there is a net flow of water from the liquid state (cloud droplets) to the solid state (snowflakes). This rather complicated chain of events is how a cloud freezes.

[Pilot DAR]

Wow, This thread has an amazing life! It has outlasted snow in Canada in February! It is supposed to rain and freezing rain today (so I'm not going flying!).

I think that when I'm feeling hot in the mid summer, I'm going to ask a question about flying in snow. The opportunity to read the many posts which will follow, should give me cool thoughts for weeks!

In the mean time, the weather is kinda yuccy here today.... Does anyone have any thoughts on the flying challenges on a clear blue day in the summer, when you can see forever, and the temperatures soar to, say, 25C? Do you take any special precautions with respect to the weather for your flight? Are their any health hazards associated with the coconut fumes of sunscreen in the cockpit, when flying with the door off?

Pilot DAR

[[email protected]]

Pace - much of the post is irrelevant and to do with the different shapes snowflakes can come in with variations of humidity and temperature. I didn't post all the Meteorolgy 101 diatribe because I assumed as a pilot you knew it anyway.

Your definition of sleet, as I said before, is the US one not the UK Met Office one.

There is no such thing as a snow crystal - it is an ice crystal and when they increase in size and complexity (as water evaporates from the supercooled water droplets) they are called snowflakes.

I didn't say snowflakes are frozen raindrops - both water droplets and ice crystals in the atmosphere form the same way in that water vapour changes state and either condenses or deposits onto microscopic nuclei in the atmosphere. The only thing the jury is out on is exactly which types of nuclei trigger ice formation and which trigger condensation into water droplets.

There is some evidence to suggest that airborne bacteria may be a major contributor to ice crystal formation and subsequently snow formation.

I'm sure we'll get back to a 'pure snow' argument again soon.

[Final 3 Greens]

Does anyone have any thoughts on the flying challenges on a clear blue day in the summer, when you can see forever, and the temperatures soar to, say, 25C?

Carb ice.

Read the accident reports and weep.

[bookworm]

I wrote:

No, that's the whole point. A lower probability of icing in the cloud that is producing the snow/sleet, because the presence of snow is an indicator of glaciation and the probable absence of supercooled water.

to which crab replied:

The weakness in your argument is the use of the word probable here - the fact is that to produce snow in the first place you must have supercooled droplets so that the water can evaporate from the droplets and form ice crystals on the freezing nuclei (the Bergeron-Findeisen process).
So, since both will exist in varying amounts depending on the conditions you cannot say with any certainty that the snow cloud will be a lesser icing hazard than the no-snow cloud.

The question of whether snow is an indicator of reduced supercooled water provoked some research on my part, because I really wasn't sure of the cloud physics of glaciation when I wrote the words above. The point about certainty remains a good one -- there will rarely be a guarantee when it comes to icing. Nevertheless, I thought this was worth sharing. The papers I cite are available as full text online, links at the bottom.

The Bergeron Process is one of many competing processes going on in the cloud. The cloud microphysics models tend to consider water in six states: water vapour, cloud water, cloud ice, hail/graupel, rain and snow. The processes that cause transition between these states are complex -- Lin et al consider between 20 and 30 of them, of which the Bergeron process is just one. If I'm counting correctly, there are 9 responsible for snow formation. In Lin's model example, the Bergeron process turns out to be significant, but not the most significant process in snow production -- simple accretion of cloud ice and cloud water by the snow is the most effective in making more of it.

Reisin et al have a more sophisticated model involving nucleation, though the phases considered are essentially the same. They run the model for a number of different types of cloud e.g. maritime and continental, with different densities (low and high respectively) of cloud condensation nuclei. What is noticeable about their results is that in every case where snow is produced, the cloud water concentration has fallen to a small fraction (say 10% of its maximum) by the time significant snow is present. It's worth noting that the simulations are for cumulus cloud with a relatively high base (about 4000 ft and 4 degC), so the model is not simulating the clouds we see as producing snow on the ground. Nevertheless, the microphysical processes are substantially the same. In every case considered, the cloud is substantially glaciated (water has turned to ice) before snow is produced.

Zawadski and Szyrmer suggest ways of predicting supercooled water content (SWC) from radar reflectivity. That paper is interesting for the assertion (based on another Zawadski paper) it makes in the introduction:

"In a study of the development of microphysics in an
Atlantic storm, Zawadzki et al. (1993a, henceforth to
be referred to as ZOL) showed that during the devel-
opment of a precipitating system, the SCW appears as
a transient phenomenon during the uplift of initially
clear air. Once precipitation develops within the super-
cooled cloud and snow grows at the expense of the
liquid, SCW vanishes rapidly. It is also possible for
SCW to coexist at equilibrium with snow if the vertical
air motion is strong enough so that the rate of the gen-
eration of water vapor excess overcomes the rate at
which snow grows by deposition."

Much of the rest of the paper is about working out the critical vertical velocity that permits SCW to coexist with snow. I'd interpret it as saying that some pretty substantial updrafts are required to make that possible. The more snow, the more difficult it is for SCW to exist.

Then finally, there's the paper that describes the NWS/FAA Current Icing Potential (CIP) model. CIP is a real-world prediction of icing potential, and is quite sophisticated. You can see the output here (http://adds.aviationweather.gov/icing/icing_nav.php). The paper describes how data like numerical model output, satellite, METARs, radar and PIREPs are combined to reach the prediction of icing potential.

"In a similar situation in which only snow is reported
at the surface, ice crystals are clearly present beneath
and within the lowest cloud layer. These crystals scav-
enge SLW through riming and may completely glaciate
the cloud (Geresdi et al. 2005). In such cases, CIP de-
creases the maximum possible icing potential somewhat
by including a snow factor in the equation (see Table 2).
When the snow is associated with widespread radar
echoes of greater than 18 dBZ, there is likely to be an
abundance of large ice crystals aloft, implying more
riming, and the icing potential is further lowered. As
more of the grid box is filled with snow echoes, this
factor becomes stronger, further decreasing the poten-
tial for icing."

All that leads me to the same conclusion: seeing snow falling from a cloud significantly reduces the likelihood that the cloud will offer a significant icing hazard. Whether "significantly reduces" is good enough in the circumstances is a rather different debate!


Bulk Parameterization of the Snow Field in a Cloud Model (http://ams.allenpress.com/perlserv/?request=get-abstract&doi=10.1175/1520-0450(1983)022<1065:BPOTSF>2.0.CO;2&ct=1)
Journal of Applied Meteorology
Volume 22, Issue 6 (June 1983)
Yuh-Lang Lin, Richard D. Farley, and Harold D. Orville


Diagnostic of Supercooled Clouds from Single-Doppler Observations in Regions of Radar-Detectable Snow (http://ams.allenpress.com/perlserv/?request=get-abstract&doi=10.1175/1520-0450(2000)039<1041:DOSCFS>2.0.CO;2)
Journal of Applied Meteorology
Volume 39, Issue 7 (July 2000)
I. Zawadzki and W. Szyrmer, S. Laroche

Current Icing Potential: Algorithm Description and Comparison with Aircraft Observations (http://ams.allenpress.com/perlserv/?request=get-abstract&doi=10.1175/JAM2246.1)
Journal of Applied Meteorology
Volume 44, Issue 7 (July 2005)
Ben C. Bernstein, Frank McDonough, Marcia K. Politovich, and Barbara G. Brown, Thomas P. Ratvasky and Dean R. Miller, Cory A. Wolff and Gary Cunning

Rain Production in Convective Clouds As Simulated in an Axisymmetric Model with Detailed Microphysics. Part I: Description of the Model (http://ams.allenpress.com/perlserv/?request=get-abstract&doi=10.1175%2F1520-0469%281996%29053%3C0497%3ARPICCA%3E2.0.CO%3B2)
Journal of the Atmospheric Sciences
Volume 53, Issue 3 (February 1996) pp. 497–519
Tamir Reisin, Zev Levin, and Shalva Tzivion

Rain Production in Convective Clouds as Simulated in an Axisymmetric Model with Detailed Microphysics. Part II: Effects of Varying Drops and Ice Initiation (http://ams.allenpress.com/perlserv/?request=get-abstract&doi=10.1175%2F1520-0469%281996%29053%3C1815%3ARPICCA%3E2.0.CO%3B2)
Journal of the Atmospheric Sciences
Volume 53, Issue 13 (July 1996) pp. 1815–1837
Tamir Reisin, Zev Levin, and Shalva Tzivion

[[email protected]]

Bookworm - some good info there - I think everyone has improved their knowledge of snow formation as a result of this thread.

I still think that my statement So, since both will exist in varying amounts depending on the conditions you cannot say with any certainty that the snow cloud will be a lesser icing hazard than the no-snow cloud.
Holds true since you cannot say that there will be no SCW/SCD, even if it is snowing and, since you have no way of measuring the SCW/SCD content, you are better off assuming that icing conditions exist.

[Pilot DAR]

Quote:
Does anyone have any thoughts on the flying challenges on a clear blue day in the summer, when you can see forever, and the temperatures soar to, say, 25C?
Carb ice.

Read the accident reports and weep.


Are there accident reports suggesting that carb ice was a risk factor at any temperature, on a clear blue day, when you can see forever?

I'll watch for it today when I fly, it's a clear blue day out there...

Pilot DAR

[Final 3 Greens]

Are there accident reports suggesting that carb ice was a risk factor at any temperature, on a clear blue day, when you can see forever?

Not at any temperature, you are safer when it is cold or very very hot.

It's also type dependent in my experience, as in airframe/engine combination.

Thus in a PA28 you'd be unlucky, in your trusty mount you'd have to be a little more careful in high humidity conditions.

It may also be location dependent, e.g. my local field

35007KT 310V030 9999 FEW015 14/11 Q1017 NOSIG, looking out of the window, you can see forever, but it is quite humid.

No big deal if you regularly check the carb heat.

[Pace]

Crab

Icing conditions may exist if there is visible moisture and the temperatures are correct for icing to occur.
But the keyword is visible moisture and whether there is snow there or just plain rain is irrelavant.

You should fear taking off into rain with no snow equally as much if the temperatures are in or near freezing.

The danger of implying otherwise is some poor S*D is going to tremble in his boots because of snow being present but happily take off into rain.

Snow looks cold and icy but its the temperature he should be looking at and the visible moisture not the snow.

Pace

[[email protected]]

Pace - unless it is freezing rain which requires specific conditions to form and is well forecast, taking off into rain is not a problem. You need to be in cloud (if that is what you want to call visible moisture) below 0 degrees to be in icing conditions.

Snow is not visible moisture it is ice.

Carb icing can occur in humid environments at up to 30 degrees C OAT.

[bookworm]

I still think that my statement ... Holds true since you cannot say that there will be no SCW/SCD, even if it is snowing and, since you have no way of measuring the SCW/SCD content, you are better off assuming that icing conditions exist.

I agree, and if you're looking for absolute certainty with regard to icing, the guidance is simple -- don't enter cloud below freezing.

[RatherBeFlying]

Here in Canada, I can not remember any accident or incident where snow by itself brought down an aircraft as long as carb ice or alternate air were used if called for. The Transport Canada Aviation Safety Letter is replete with sermons on several common ways to crunch an aircraft, but I don't remember any article that declared snow by itself would bring down an aircraft; mind you, carb ice or alternate air may be required in some cases -- and if your helicopter's operating limitation prohibit operation in snow, then don't.

That said, whiteout and CFIT are hazards and if there's a significant snow shower over a runway, I'll not be using it until the snow shower has moved away. In fact, I may decide to land elsewhere.

And it won't hurt to carefully check out destination airfield conditions as there's lots of accidents where a wingtip has struck a snowbank on landing or during taxi:ouch:

And please don't try taking off with any snow or frost on the flying surfaces.

[scooter boy]

"freezing rain which requires specific conditions to form and is well forecast"

What forecasts are you looking at Crab?

SB

[Pace]

Pace - unless it is freezing rain which requires specific conditions to form and is well forecast, taking off into rain is not a problem. You need to be in cloud (if that is what you want to call visible moisture) below 0 degrees to be in icing conditions.

Snow is not visible moisture it is ice.

Crab :ugh: who is saying snow is visible moisture? certainly not me! taking off in rain at the wrong temperature most certainly is a problem in or out of cloud.

Give me nice puffy snow flakes any day of the week :)

You will get rain out of clouds as well as in clouds. That may fall as rain as you climb through the clouds but then when the temp drops to zero that rain will start to form as ice on the airframe.

Pace

[[email protected]]

Pace - Icing conditions may exist if there is visible moisture and the temperatures are correct for icing to occur.
But the keyword is visible moisture and whether there is snow there or just plain rain is irrelavant.


The last sentence of that quote implies you view both snow and rain as visible moisture - it may not be the way you intended it to be read but thats how it comes across to me.

You will get rain out of clouds as well as in clouds. That may fall as rain as you climb through the clouds but then when the temp drops to zero that rain will start to form as ice on the airframe.

Not quite sure what point you are trying to make here - all you have said is that icing conditions exist in cloud below zero, which we all knew anyway:ugh:

taking off in rain at the wrong temperature most certainly is a problem in or out of cloud. How is taking off in rain a problem unless it is freezing rain? If the OAT is above zero it's not freezing rain because the airframe is above zero - I think this was one of your points many posts ago. If you are in cloud below zero you are in potential icing conditions whether it is raining or not.

Scooter Boy - I was trying to make the point that freezing rain is relatively easy to forecast because it generally requires quite specific conditions to exist (active warm front, sub zero layer beneath etc)

[Pilot DAR]

Wow, this is certainly going around and around.....

My point was missed; "clear blue day in the summer" = no moisture in the air = no risk of icing, temperature is irrelevent.

I would be much more fearful of flying in rain near freezing, than snow in any temperature. Yes, you can have "rain" below freezing, and "snow" a little above. "Snow" decribes a form of "ice", which is frozen, so it's not gong to freeze again (on your plane).

Would you rather fly your beautifully painted plane through paint dust (which is floating solids of paint - not sticky) or paint mist (which is floating liquid)? Your plane won't be bright pink after flying thorugh the pink paint dust, but it surely will after you fly throught the pink paint mist!

As I said somewhere around the beginning of this thread, the choice to launch into percipitation must be very carefully considered, and particularly in the context of training, experience, and comfort level of the pilot. If in doubt, don't go! The fact that one pilot doubts, does not mean another cannot fly safely!

If you want to learn, great! Read, write, ask, and try to wangle some right seat time with someone who has done this before. It's just amazing what you can learn from the wise and experienced person, who is very comfortable doing that which you have yet to try!

I regularly fly in snow, and in rain. If the percipitation can't decide which it is, I'm happiest on the ground!

Pilot DAR

[Pace]

If you want to learn, great! Read, write, ask, and try to wangle some right seat time with someone who has done this before. It's just amazing what you can learn from the wise and experienced person, who is very comfortable doing that which you have yet to try!

I regularly fly in snow, and in rain. If the percipitation can't decide which it is, I'm happiest on the ground!

Pilot Dar

there are those that do and those that talk about it. I second your comments above as until a pilot has experience in dealing with certain situations and conditions no amount of talking can fill a void of lack of experience.
Like you I would rather take off into snow than rain near freezing point and like you I would recommend a PPL flying with an experienced pilot to get that practical immersion in the real conditions and in an aircraft/pilot combination able to deal with with those condiitions

Pace

[bookworm]

Wow, this is certainly going around and around.....

Never get into a circular argument with a Rotorhead -- you get dizzy and the Rotorhead enjoys it. :)

(with appropriate apologies for the poetic licence...)

[Pilot DAR]

Yup, I'm a rotorhead too...

[Final 3 Greens]

My point was missed; "clear blue day in the summer" = no moisture in the air = no risk of icing, temperature is irrelevent.

Today, I climbed up the bell tower at a local church.

I could clearly see the upper parts of a mountain about 100nm away.

Air temp was 19 deg C and the RH was 78%. To be fair, despite the blue skies, there was some cloud at FL250. I know this, because I took a self brieifng from the airport.

Maybe it's different in Canada, but your point was not missed.

If the RH is high, carb heat can get you in the mid 20s, I've experienced it in the UK on a warm, sunny, clear 23 C day, in a Beagle Pup with a Continental O-200.

[birrddog]

Having just read through this thread, I think it is important for the definitive definition and appreciation of 'pure snow'.

I trust you are now 'informed'.

cmoGVo_oI_g