Dangers of flying in snow

[topcat450]

After nearly getting caught out in a snow shower yesterday (I could see the snow just hitting the far end of the runway as I was on very short final), i was curious what were the main dangers of flying through a snow shower?

Is it just the (seriously) reduced viz? Will is cause airframe icing or at 80kts will it just 'blow' right off?

Editing to say - and yes... I learnt quite a bit yesterday so try not to just abuse me for cutting it so close, I've beat myself up about that plenty.

[timmcat]

i was curious what were the main dangers of flying through a snow shower?

eeerm... a rapid cessation of flying would be a tad disappointing one would think...

(OK - non flyer prooner will now skulk off back to JB..)

[Aim Far]

I ended up flying in a snow shower at the weekend for a couple of minutes. It was quite fun - a bit like the stars on the old windows screensaver. I had a way out - I was skirting round the edge of the cloud - so I wasn't too worried. The snow wasn't sticking to the airframe, maybe it was too cold? I suppose the problem is you just can't tell whether its going to stick or not. Other dangers would be induction icing.

[Snigs]

Apart from all of the obvious issues, it's IMC (you know, a whiteout)..... are you qualified?

[bookworm]

It's very unusual for snow to stick to the airframe in the air -- it's already frozen. Impact icing in induction systems etc. is possibly an issue. But as you've realised, the biggest problem is the white-out effect.

[Capt. Manuvar]

Unless the snow is totally dry, i wouldn't go on a flight with the presumption that the snow will blow off. Snow can be very sticky. If you are not IMC rated i wouldn't underestimate the danger of whiteout. I had a chance of flying in Canada this winter and experienced a bit of white out. In snow the visibility can decrease very rapidly.
Of course airframe icing is not a joke. I was once in a C172 that had picked up some ice and could barely maintain 80KIAS in level flight at full power.
If your a/c isn't equiped for flight in known icing you shouldn't be flying in any kind of precipitation when the temps are below frezzing which i guess it would have been when it was snowing.

[High Wing Drifter]

There was a case where a RAF Jag pilot landed well short because the maitenance crew only cleared the mid section of the runway. Beacuse the pilot just maintained the correct out of the window look he was decieved into thinking he was higher than he was.

[slim_slag]

Snow can be VFR too, but you need to be careful as that can change quickly. Good rule of thumb when flying VFR is never fly into a shower if you cannot see through it to the other side. Flying in snow is the sort of thing you need to do first with somebody who has done it before. Better to pick your way around the showers if you can. Ice can happen, snow can be 'wet', apply same rules as when flying in rain.

[Final 3 Greens]

If the snow is caused by a Cb or large Cu, there may be severe turb associated with the gust front and downdrafts - beware.

[Mosspigs]

Aside from the mechanics of the snow and control surfaces etc etc , one of the most concerning aspects of flying in snow is if VFR, the "stars" that you alluded to can cause spatial disorientation.

At the very least they can cause a distraction that could lead to break down of a scan. Unless you are a super cool pilot, if you don't have an IMC, the chances are you aren't, which you will not notice that you are climbing or descending. This can lead to a very emotional time.

[englishal]

I flew through a couple of showers on Saturday as well....no problems were experienced...

[Kolibear]

Driving through snow can be very disorientating, even mesmerising. Snow packing in the air intake system could also be a problem too, the snow can build up on any mesh filter upstream of the throttle and air filter.

[Aussie Andy]

I recently had my first encounter with serious snow in IMC - the evening before my IMC rating flight test... if you'd like to scare yourself about snow, then read this :O !!!

http://www.pprune.org/forums/showthread.php?s=&postid=1708157#post1708157 (scroll down to the paragraph beginning "Before I go..."

Essentially I was OK as we were IFR and got ourselves a radar service etc, but there were a few people VFR on the frequency at the same time all trying to get back into Wycombe - and it was a bit scary for one bloke in particular who very nearly didn't make it, but with help from D&D (three times!) he eventually got down... just!

Andy :ok:

[bookworm]

Unless the snow is totally dry, i wouldn't go on a flight with the presumption that the snow will blow off.

Lest there is any misunderstanding reading this comment in the context of mine above, I don't think that snow will stick to a clean wing in flight: if it's frozen, it's frozen -- if it's partly melted, the temperature is above freezing and icing is unlikely.

But there's a huge difference between that and assuming that snow that has accumulated on the wing on ground will "blow off" during flight. Different processes may occur when the snow starts to accumulate, and to depart with snow is at best illegal and at worst suicidal.

[Genghis the Engineer]

I've flown in snow twice, neither deliberately, and both briefly.

Once in a PA28, through light falling snow. It was rather like the ubiquitous windows screensaver, but nothing formed onto the aeroplane, and no ill effects were experienced.

The other was in a flexwing microlight, when it plastered on my helmet, arms, body and (I assume) the leading edge of the wing. It was very alarming indeed, I was basically in a total white-out - I couldn't even read my instruments. Thankfully it only lasted a few minutes (and I could maintain basic attitude information by looking out the side); by the time I landed (about half an hour later) there was none left. I didn't notice any handling problems, but on the other hand was being incredibly careful to maintain straight and level with good speed. It is not an experience I have any desire to repeat !

G

[BigEndBob]

Be very careful not to get caught out in a whiteout situation.
10 minutes of heavy snow can completely cover runways, vis can drop to 1/2 mile or less and even at 200 feet the only way you know which way is up visually is by knowing tree trunk generally point toward the sky..or is it the other way round!

[Tinstaafl]

Very common in the Shetland Islands. It takes very little snow to change VMC into IMC. Even worse, a seemingly benign snow shower can quickly become not so benign even while still flying through it.

[Mosspigs]

Aussie Andy,

Good post but doesn't put Wycombe in a good light.

400' cloud base and snow showers yet they told you to level off in cloud at 3500'. That must be icing conditions for which the PA28 isn't cleared.

That said well done for passing.

[bookworm]

Good post but doesn't put Wycombe in a good light.

400' cloud base and snow showers yet they told you to level off in cloud at 3500'. That must be icing conditions for which the PA28 isn't cleared.

Not quite sure I understand your comment. Wycombe doesn't offer an IFR Approach Control Service. Andy (or his instructor) was entirely responsible for the choice of level and route.

Even if they were providing IFR Approach Control, it's not their responsibility to decide on flight conditions. It's for the pilot to refuse any clearance for which his aircraft is not suited. If the pilot asks for a clearance at a weather that's unsuitable because of weather, it won't be withheld for that reason.

[Droopystop]

I appreciate that dry snow would not stick, but we do not get dry snow very often in the UK. Certainly in every snow shower I have flown in (and there has been a few) snow has always stuck some where on the airframe. No one has mentioned propeller icing and being a rotorhead I don't know how likely that is. But on a helicopter there is sufficient friction to keep the blades a few degrees above ambient. I am guessing that a prop at 2500rpm has more friction and is therefore warmer. So could there be a scenario where you flying in say -2degrees in snow and the prop is a freezing or even minus zero as the met men would put it and you get prop icing?

More importantly is departing just after a snow storm. Been a number of terrible accidents where wings have not been properly cleared or snow accumulated in coamings have been sucked into the engine.

But flying on a clear day after snow is breathtaking.

[Aussie Andy]

G'day Mosspigs,must be icing conditions for which the PA28 isn't clearedThanks for your concern, but in fact it wasn't icing conditions: no ice formed on the airframe whatsoever.

The CFI, who was flying with me, commented that "because it's snow it's already frozen and it won't stick": all I can say is that it did not stick! I had no problem at all maintaining speed/height etc. (any problems experienced were merely a function of my tiny brain being slightly overwhelmed by the whole experience!).

But my experience in snow is just this one flight, so I bow to others who have said that there are circumstances in which snow will stick and cause ice to form on the airframe.

It was a great experience for me however. The lesson learned that day was that, although I was happy with how I did, I am absolutely sure that as a low hrs PPL who is unlikely to fly in IMC more than once a month at the very best, I would never - ever - want to intentionally put myself into a situation like that again without a very experienced person who is highly current sat next to me in the r.h. seat!

Great thread by the way TopCat!

Andy :ok:

[FlyingForFun]

Very interesting thread, but it seems that no one has yet given a definitive answer to the original question. I don't know the answer myself, but I would like to find out.

So: We all agree that snow causes white-outs, and therefore is almost certainly IMC. We all agree that snow on the airframe before the start of the flight is a very bad thing.However, the question which hasn't been answered yet is this:

Is it safe and legal for a current, experienced, IMC-rated or instrument-rated pilot to fly a non-deiced aircraft through a snow shower? Please answer either Yes or No. Or, if you're going to answer Maybe, please give a simple way in which the pilot can determine whether an individual case is safe and legal.

I won't hold my breath for an answer, though!

FFF
---------------

[Maude Charlee]

Airframe icing occurs down to -40C in any form of precipitation. Anybody foolish enough to deliberately go chugging about in an aircraft without anti-ice or de-icing capability in icing conditions is unlikely to repeat the experiment on very many occassions.

Given the current wx in the UK, and the operational envelope of light singles, how anyone can suggest it is too cold for icing is clearly bonkers.

[englishal]

Yes:

"Usually, little, if any, icing is found in areas of snow"

NZ CAA Icing handbook. They are talking about being in cloud in snow showers, not flying through a "shower"

Just my opinion.....;)

[slim_slag]

FFF, why not apply the same question to flying in cloud? Beware the inversion!

EnglishAl, that word 'usually' says it all. Nothing is certain when you are around freezing point and liquid water is around (i.e. wet snow).

[High Wing Drifter]

Is a snow white out any worse than heading out to sea with a clear blue sky. My instructor did this on my trial flight. It has stuck with me ever since!

[Final 3 Greens]

HWD

Or indeed flying on a moonless night over an area without lights.

All three situations suggest to me that a reasonable degree of instrument flying capability/currency is a good thing to have.

[average bloke]

Some of you guys/gals should read the safety sence leaflets and have a good look through the AIP/AIC. Here is just one quote:

'Most of the time snow, which is already
frozen, will not stick to an aircraft, but
occasionally wet snow with a high
moisture content will stick. Treat it like ice.'

This is not to mention a whole host of reasons why flying an aircraft that is not certified to fly in known icing conditions into such conditions is nuts. how about engine icing, stall warner icing, landing gear icing, windscreen freezing, etc, etc.

how can you tell when flying into a shower (cu, tcu or cb) whether the snow will be frozen/moist/sleet or not, when the conditions under such a cloud may be turbulent, with updraughts/downdraughts, pressure changes, temperature changes etc. remember super cooled water droplets?

In answer to FFF's question - if it is not certified to be flown into known icing but you do anyway it is not legal. it is also not safe.

[Croqueteer]

Ask Buddy Holly.

[Aim Far]

I don't really consider myself nuts or bonkers or foolish.

If I don't know what a particular weather condition is going to be like, I have two choices. Try it. Or read a book and avoid experiencing it in real life.

IMHO, the key is not to avoid altogether but to have alternatives. If you can see the other side, if you know the cloud top is only a little bit higher, if you have sea/flat land beneath you, if you saw some sunlight just up ahead, if you can turn round, you have options. If you're in a low wing aircraft, you can see if you are getting build up of snow and use one of your options. Having alternatives is more important than mindless avoidance based on something rote learned from a book.

There is no right or wrong answer to whether flying in snow is safe; it is a matter of degree. Sometimes it is not a big deal, other times it could be. As pilots, we should be evaluating the situation all the time.

[bookworm]

how can you tell when flying into a shower (cu, tcu or cb) whether the snow will be frozen/moist/sleet or not, when the conditions under such a cloud may be turbulent, with updraughts/downdraughts, pressure changes, temperature changes etc. remember super cooled water droplets?

So your advice seems to be that it's unsafe to fly through any cumuliform cloud under any circumstances, at any temperature, just in case you encounter something nasty which happens to be at a different temperature?

IMHO, the key is not to avoid altogether but to have alternatives.

I think you hit the nail on the head, Aim Far. It\'s my firm belief that your attitude will keep you alive rather longer than an approach that avoids any exploration of hazards.

Realism in risk management is vital in aviation, not just to make aviation operationally viable, but because we have to make decisions based on relative risk. If we over-estimate risk in one area, we drive our decision towards actions that are actually more risky than the best overall strategy. Do you fly over the hills to avoid the snow shower in the plain?

Average bloke has taken an ambiguous passage from an SSL which I think otherwise gives pretty good advice. It\'s important to appreciate the hazards, without overestimating the risk associated with snow.

[Final 3 Greens]

Whilst agreeing with Bookworm's argument, my only rider (from experience) is that decisive decision making is required of things go pear shaped.

Ice builds up surprisingly quickly under some circumstances and immediate action is required.

I make this point not to score points, but as a caveat to any relatively new PPLs reading the thread.

[bookworm]

And it's a rider with which I strongly and wholeheartedly agree, F3G.

I suppose one of the reasons for the strength of my reaction in this thread is that treating snow as an inevitable significant icing hazard almost trivialises the monster that icing can be.

[average bloke]

So your advice seems to be that it's unsafe to fly through any cumuliform cloud under any circumstances, at any temperature, just in case you encounter something nasty which happens to be at a different temperature?

No. If you read the title of the thread it refers to flying in snow. My point is that you should not assume it will not stick, as some people seem to think, and that you should treat it as ice. This is also the opinion of the CAA. If icing conditions exist, then you should not fly in them deliberately unless the plane is certified to do so. Period.

mindless avoidance based on something rote learned from a book.

I fly for a living.

It's my firm belief that your attitude will keep you alive rather longer than an approach that avoids any exploration of hazards

Bookworm, IMHO flying is about first of all ensuring the safety of people on the ground, your passengers, and finally yourself. If you can 'explore hazards' whilst doing this then you have my support.

Also, if planning to fly in IMC, and icing conditions are possible, you should ensure you can be out of them at or above your MSA. This can prove tricky when freezing levels are low or on the ground.

I love flying VFR/IFR in all sorts of weather, but ice is a killer and should be treated with the utmost respect.

[englishal]

Its funny how flying through a *snow shower* has turned into flying IFR in icing conditions ;)

I don't think there is anything dangerous about flying through a snow shower which you can see through, see around, see down and know you'll be out of in a few minutes. I'd never flown in one before so thought we'd try it, with plenty of space to get out.

Still, each to their own opinion......

[Mike Cross]

On snow=good
In snow=bad

http://michael.cross20.users.btopenworld.com/images/webimages/qt.jpg

Cumulo-Granitus not recommended
http://michael.cross20.users.btopenworld.com/images/webimages/cugr.jpg

http://michael.cross20.users.btopenworld.com/images/webimages/final2.jpg

[Aim Far]

I fly for a living
Good for you.

But if I was your student and asked "what's it like to fly in a snow shower", I'd want an answer, not a lecture.

[Aussie Andy]

Well, I had a lovely flight today - including through some of the light snow showers that were around... so light you could mostly see through them. It was very pretty up there today - lovely vis!

Andy :ok: