Hoverbover: apologies for getting overheated about snow!!

Tiercel: There are very few, if any 'current' civilian helos that are allowed to fly in icing, and the definition of icing is: flight in visible moisture below 0 degrees celcius (in the UK anyway). This includes snow. That's why I said "do not fly".

CTD: I was based at Shearwater on exchange to 423 sqdn for 3 years in early 80's. Did a couple of cross country's to nanaimo (if I remember the spelling) and stopped en route to do glacier and snow flying. Also flying off frigates from St Johns harbour because the ship was stuck solid in sea ice!!
Were you a mil pilot with the air force too?



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Thermal runaway.

No, I was on the civvie side. Mainly Newfoundland in the 80's, Labrador and the Arctic in the 90's, with a couple of shots over in Asia and Africa to warm up in between :)

As for your 'no flight in visible moisture below 0ºC', good thing we don't have that regulation in Canada, there'd be no point to have helicopters! Excuse my ignorance, but is that applicable even if the aircraft is properly equipped with snow deflectors or the equivalent?

Randy, Tiercel, IHL, you're all from Canada, did you guys know that.....?

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Crash Test Dummies are people, too.

To TC

No appologies needed, There is just SNOW way I want you two to fall out.

regards
hoverbover


[This message has been edited by hoverbover (edited 08 March 2001).]

the regulations don't state what "icing" is, just that you're not supposed to knowingly fly into conditions conducive to it.... 'visible moisture below freezing' is what you learn in training, and I think it is accepted that snow is exempt.

Thomas Coupling,

As a mil pilot I was under the impression that rotor and airframe icing conditions are defined as cloud or fog within the temperature range 0 deg C to 30 deg C true, WHEN THE VISIBILITY IS LESS THAN 1000 METRES. Visibility reduction due to snow alone does not constitute an icing condition.

There are different rules for icing conditions (no go) and for flying in snow (dependent on viz/temperature)

http://www.stopstart.fsnet.co.uk/smilie/wokka.gif

Wow, Ed! What sort of ice forms at 30 C? I take it you mean minus 30?

Yikes !! CTD I don't know the British regs, but if it could be interpreted that way... If we had a reg that could be interpreted that way, very few would be flying during the winter.

On that note, today is moving day and back to the Great White North. Talk to you guys :)

Cheers

Randy_g


Now where the heck did those heater controls go !!!! :)

Ed Winchester: that brings back memories, and yes that was the statement I was looking for (albeit -30 degrees!!). The mil fine tune it to some degree by putting a figure on it (1000m, probably because thats the dividing line between fog and mist?).

However I'm sure the mil also restrict snow to flying in those conditions 'below 500m' do they not?

You failed to mention also that precipitation is also included in the definition. In fact any precip in this range incurs some kind of airframe or engine icing actions. I would suggest that since rain/drizzle is precip, then so too is snow. Wet snow most certainly is.

CTD: My definition of visible moisture is rain / fog / cloud / snow / anything with water molecules in it. Provided you stay away from this then one can fly down to whatever the FLM tells you: -30 degrees for example. So flying around sub zero is a very common practice over here too!! but not in visible moisture, unless that particular model is specially fitted for sub zero flight envelopes (EC155, S76, puma, S61 for example).

[I know that below a very low temp (can't remember offhand I think it's -20 degrees?) one encounters supercooled droplets and yet lower than this: ice crystals, where a/c fly because they have negligible effect on the airframe, but that's not helo territory, I believe!]

Open to scrutiny??

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Thermal runaway.

[This message has been edited by Thomas coupling (edited 09 March 2001).]

Shy Torque,

I'm gonna have to get up early to catch you out!

Tom C,

Close, but no cigar!

"You failed to mention also that precipitation is also included in the definition" (one too many also in there!)

That is because it isn't in the definition. The definition is verbatim.

So, flight in rotor and airframe icing conditions or hail or freezing rain/drizzle is prohibited.

As I said, VISIBILITY REDUCTION DUE TO SNOW ALONE DOES NOT CONSTITUTE AN ICING CONDITION. So we can fly in it.

"However, I'm sure the mil also restrict snow to flying in those conditions 'below 500m', do they not?"

Mate, I have not got a scooby what that question means!

If you mean do we have some restrictions to flying in snow, then yes. Obviously it will be different for each type.

For instance:

Flight in falling snow IS PERMITTED in OAT down to minus 30 deg C subject to the following:

(1)Flight is permitted in falling snow of any severity in OAT colder than minus 4 deg C. Flight must be in VMC and visual contact must be maintained with the ground.

(2)Flight in visibilities of less then 400m in OAT of minus 4 deg C or warmer must be avoided.

Finally, as you rightly suggested, WET SNOW is a hazard, and so, flying in recirculating snow at minus 4 deg C or warmer is kept to the mimimum.

Cheers,

Ed

PS. I'm off to Canada in the near future to fly for three years, so I look forward to flying in real snow, not the 1/2 inch covering which seems to grind this country to a halt!

http://www.stopstart.fsnet.co.uk/smilie/wokka.gif

[This message has been edited by Ed Winchester (edited 09 March 2001).]

To Everyone
Thanks for everyones input so far.
As I started this thread I was unsure of many things, and am learning all the time.

In flight below -10 C OAT airframe icing does not occur, is this correct or is at a fixed wing thing?

In the RFM the heli I fly is cleared for flight in blowing and falling snow,(providing the particle seperator is fitted)
but has no temp ranges.But is not cleared for flight in known icing.So is flying in snow below 0 C greater than3000m vis correct/incorrect.

I am a little confused at to what constitutes icing conditions.Does snow below zero C but greater than 1000m vis constitute icing conditions (just curious not thinking of flying in it)

regards
hoverbover

PS
Posted this just as ED Winchester posted his,hence I hadn't seen his post,very informative.Cheers

Ed Winchester
Have a good time, just dont fall asleep on the way home from the Pub in winter !!!!!


[This message has been edited by hoverbover (edited 09 March 2001).]

Hoverbover,

Put simply, icing conditions are conditions where icing will build up somewhere on your aircraft. Depending on aircraft type it may be the engine intakes or elsewhere on the airframe that is most critical. It isn't possible to generalise too much because each type is different. Icing trials have to be carried out to determine limits / clearances for each type of aircraft.

Ice accretion rate depends on:

Temperature: Above OATs of zero C there is unlikely to be airframe ice, but engine intake pressure drop may cause local temperature drop to zero or below; hence a requirement for engine anti-ice on around 5 degrees C for turbine aircraft. Local heating (e.g. of the outer part of main rotor blades by air friction) may delay ice accretion on some parts of the airframe. Be aware that well below zero c precipitation can remain unfrozen till it hits your aircraft (down to minus 10 rings a bell but I might be wrong - if so someone please correct me.

Total water content: Simple, more water = more ice.

Droplet size: Affects the rate and type of accretion. Small droplets tend to freeze rapidly and form whitish (trapped air), low density, brittle ice. Large, supercooled drops are perhaps most dangerous as they freeze relatively slowly on airframe contact (contain more latent heat) and flow backwards in the airflow. This type of clear ice is "sticky" i.e. adheres more strongly to the surface and it is relatively dense and heavy. Rain ice is an extreme form.

Airspeed: Increasing airspeed cause more rapid droplet contact and increased accretion rate until about 400 kts when surface heating by air friction takes over and reduces it again.

Shape of the affected surface: Droplets have inertia and they cannot change direction as rapidly as the air supporting them. Thinner objects tend to collect more ice. Wider, more rounded ones collect less in the same conditions as the droplets can smoothly follow a gradual path change, although ice may form very rapidly at a stagnation point at the front of an object e.g. on the aircraft nose or ahead of a fairing, depending on design. The windscreen wiper arms are often a good indicator of what might be happening further back on the airframe. Some aircraft have an ice accretion probe (with a thin profile) fitted where the pilot can see it. Flight in icing conditions may then be allowed by the aircraft manufacturer until a certain ice build up occurs.

To my knowledge, the Super Puma is still the only helicopter cleared for unlimited ops in icing conditions. It has electrically heated blades, windscreens, intakes and other surfaces powered by an extra generator, covers over the control rods to main and tail rotors etc etc.

The best advice for helicopters and icing conditions is to vacate the conditions or adopt the "LOALI" principle.

"Land On And Leg It"!

Good explanation Shy. Your -10º analogy is generally correct, but the water has been known to stay in a supercooled state down to -25º.

The problem with icing is that it there we do not have a substantial body of knowledge on the subject. There are so many factors involved in its formation and accumulation, that accurately predicting its effect on a given flight regime is impossible. Something like predicting the weather....we know the general rules, but the complexity of the system defies our ability to accurately and precisely predict it.

As you said, stay out of it. Period.

Shy Torque and CTD,

Good stuff and wise words indeed - stay out of icing conditions!

Just found a UK CAA AIC I had in mind. It is AIC 93/2000 (Pink 8) dated 19 Oct, entitled Frost, Ice & Snow on Aircraft.

This may be of some guidance.

ShyT

Good thread.

CTD, I got your e-mail but I deleted it before I got your address. http://www.pprune.org/ubb/NonCGI/frown.gif Send me another please.

Excellent topic ,learning loads
i did a litle helisking in italy p2 and now i know why they did all that stuff , my italians not that great.
The one thing they used to do if at all posible was to do a really shallow approach and stay on the edge of translational lift , slowly moving foward to the landing site , this gave us a good idea how sticky the snow was , ie if it was going to cause a white out or if it had crusted in the top layer
also gave us an idea how deep the snow was and if the terrain was suitable.
ps , make sure they hold the skis horizontal , they dont mix well with Rotors

Ciao.

:)

A BIG THANK YOU to everyone who has posted ti this thread, I hope others have learned as much as me,and also how little I knew in the first place!

Again thanks to everyone for their time and effort

Regards and safe flying
hoverbover

Bearpaws & snow
 

Hopefully someone may have a solution, but we are often distracted in the snow by calls of "something's fallen off your 'elicopter". Needless to say, it's always a chunk of snow shedding from a bearpaw, after take off. At least, so far it is ;)

Any snow operators (Canadians or Kiwis, I'd guess) have this problem, or even better, a feasible fix? Bearpaws are Dart style thermoplastic jobs, only on the aft end of the skids.

TIA

Having operated for many years in the snow with bear paw equipped aircraft, I'm not sure how to answer. I can't recall having anyone ever call me up on the radio to say they had seen something come off my aircraft just after takeoff.

I'm a little curious, do you get this a lot or just once in a while? Most of the passengers I flew in those years tended to be seasoned helicopter users. I don't know if that made a difference.

Nothing leaps to mind as to a fix for this. I kind of suspect it's just something one has to live with if using bear paws. :)

I used to have calls frequently the first season (5 years ago), but now it's just occasional enough to be a nuisance. Last Monday was the local police out playing on their skidoos, convinced that something important had fallen off!

We're operating from resort to resort, thus sometimes overflying downhill runs or lift lines, so we have a huge number of interested onlookers. 40 flights a day means we're bound to get a call or three, plus patched in to the resort radios means we can't hide :D