What are 'Icing Conditions'? [Archive]

ShyTorque

19th Feb 2009, 19:45

Obviously, water can't freeze until it meets a temperature of 0 degrees C.

Can this occur in the engine intakes, or plenums, for example? If so, you might encounter an engine icing situation although the airframe remains ice free.

Water can exist in a liquid state below that temperature, if there is nothing for droplets to freeze onto or around (supercooling). If the airframe, or part thereof, is below zero and it meets supercooled water droplets - you then almost certainly have icing conditions.

One other consideration - how accurate is the OAT guage on a particular aircraft?

In my outfit, if any build up is noticed (the wiper blades are an excellent indicator) THAT is icing conditions. However, as always, the Flight Manual is the paramount authority.

Whirlygig

19th Feb 2009, 19:57

According to some (http://www.pprune.org/private-flying/360501-flying-snow.html), snow is OK :} :rolleyes:

Cheers

Whirls

paco

19th Feb 2009, 19:59

I would imagine it is when the met office report that they exist. And bear in mind that the FAA regard "forecast icing conditions" as "known icing conditions".

You could also infer it from the flight manual from when the anti-icing needs to be on - e.g. +4.4C for the 206, but Robinson have also issued warnings for +30 in humid conditions, so my own inclination to take the one the jury would take notice of!

Phil

chopjock

19th Feb 2009, 20:46

Can anyone, using their encyclopedic knowledge and experience illuminate me on what temperature you can LEGALLY fly in visible moisture to remain within the parameters detailed in the AFM????I'm not sure that it is against the law to fly in visible moisture (icing) conditions or outside the parameters detailed in the AFM.

I am sure it would be unwise though.
:hmm:

Canuck Guy

19th Feb 2009, 20:59

Like Phil says, the met reports are a great place to start looking for icing conditions, be it forecast icing or pireps showing icing encountered by others inflight.

Icing is an odd thing though and can be found in a range of conditions. I've flown IMC at -2C and never picked up any ice at all. On another day I flew thru a small localized rain shower at +5C and to my surprise watched the water freeze on contact with the window. :eek:

Shawn Coyle

19th Feb 2009, 21:04

Be careful. Icing is defined in Appendix C of Part 27 and 29, but it only covers water droplet sizes up to 50 microns - that's 0.5mm (or the thickness of a mechanical pencil lead). In that condition, the droplets are more or less suspended in mid-air.
Anything larger than 0.5mm is considered to be freezing precipitation - and no aircraft (fixed or rotary wing) is cleared for flight in those conditions. So if it's not snow, and you encounter something falling from the sky and freezing, stay on the ground.

malabo

19th Feb 2009, 21:06

Depends on the jurisdiction. Like Paco says, different authorities have different definitions. Some look only at an OAT gauge, some look for ice on sponsons or wipers, some look at the torque gauge, some look at a weather forecast. In some places regardless of what is forecast, if some brave ice-dummy soul ventures up and reports back that he isn't picking up ice then to the rest of the pilots it is no longer "Known Icing", in fact it is now "Known Not To Be Icing".

Pilots in places like Norway or the Canadian North that wouldn't turn a blade from September to April following the rules of more temperate locales, have built up a vast body of knowledge based on experience. Such as Whirl's comment on snow. This is passed down from senior pilot to junior pilot. As it should be.

JHR

19th Feb 2009, 21:44

The FAA has recently produced a legal interpertation defining known ICE for flights in the USA. As most guidance from the FAA it is not very usfull, if you get in trouble on a flight in iceing conditions you get hung out to dry. If the flight is completed ok you are ok, go figure.

The FAA also defines known ice in the Aeronautical Information Manual as ice observed accumulating on the aircraft.

The link for the interpertaion is below.

Regulations (http://www.faa.gov/about/office_org/headquarters_offices/agc/pol_adjudication/agc200/Interpretations/)

Overdrive

19th Feb 2009, 21:54

up to 50 microns - that's 0.5mm

Isn't that 500 microns? Or 0.05 mm?

krypton_john

19th Feb 2009, 22:04

Shytorque, I guess you do know already that ice can form at *ambient* temperatures above zero where there is a cooling effect from expansion - the obvious example being carb icing. But would such an effect occur on the airframe? Any low pressure area could be a candidate, such as behind slots in flaps, behind objects projecting into the airstream etc.

ShyTorque

19th Feb 2009, 22:24

Yes, I am very much aware of the individualities of airframes. Follow Whirls' link and look at my argument on that discussion, which was in a nutshell that generalities are dangerous things to believe. In that instance one contributor was quite adamant that snow could not stick to an airframe - I disagreed. Icing trials, particularly on helicopters, need to be very carefully carried out for a meaningful icing clearance to be issued. Subsequent experience in a variety of conditions may result in a clearance being further restricted or eased.

ppng

19th Feb 2009, 22:36

Don't quote me, but I think there is a UK definition of Icing Conditions as "flight in visible moisture with an OAT of 0C or less, with a visibility of 1km or less".

[email protected]

20th Feb 2009, 07:26

JHR - you are right, that letter from the FAA isn't overly helpful. On one hand it says that known icing conditions only exist when you see ice accumulating on the airframe but on the other they say a pilot who flys into an area where icing would probably be encountered (based on met forecasts and reports) is OK if they don't encounter ice but might be prosecuted if they do!

If potential icing conditions exist ie less than 1000m vis with OAT below zero - then as long as you have what the FAA call 'an icing exit strategy' you are pretty much acting within the letter and the spirit of the RFM.

The problem with helicopters is that once you start to accrete ice you often don't have the power/performance to climb and only a limited ceiling anyway so you are forced into descent into clear/non icing air or a turn back to a known clear/non icing environment.

So if your enroute met looks icy all the way to the deck it might be time to say no.

fkelly

20th Feb 2009, 08:58

once you start to accrete ice err... accrue, shurely?

cjbiz

20th Feb 2009, 09:33

fkelly

ice 'accretes' to an aircraft ie attaches itself to the airframe. your bank account 'accrues' interest or more likely if like most of us on here...your scarily increasing overdraft accrues charges!!! :E

biz

Claude Yervestov

20th Feb 2009, 12:16

Shytorque mentioned that "you might encounter an engine icing situation although the airframe remains ice free" ... the following definitions appear in one of my company's limitations documents:

"Rotor and airframe icing conditions are defined as cloud or fog in the temperature range 0ºC to –30ºC when the visibility is less than 1,000 metres" (where –30ºC is the bottom end of the aircraft environmental envelope). However ... "Engine icing conditions are defined as cloud or fog with visibility less than 1,000 metres, or rain, all in the temperature range of +10ºC to –30ºC". (The increased upper limit (+10ºC) recognises the cooling effect of the engine intakes ...)

The same document also includes the following comment: "Due account must be taken of the limit of accuracy of the OAT indication, which is ±1ºC".

CY

check

20th Feb 2009, 13:16

"Flight in icing conditions prohibited", so says the Flight Manual.
I read this, and luckily so does my company as "conditions conducive to icing" i.e. 0 degrees, visible moisture, viz below 1000m etc. If such conditions are forcast on your route you should avoid it. By penitrating the area you are in breach of the limitation section in the flight manual.

The word "conditions".

As a verb: To make dependent on a condition or conditions.
As a noun: a circumstance indispensable to some result; prerequisite; that on which something else is contingent.

Both come up with the same answer. a number of prerequisites occuring together to give in our case Icing.

There is a subtle difference between flight in icing conditions and flight in icing.
The first, your going to get it, the second, you've got it.

[email protected]

21st Feb 2009, 07:23

Check - yes but Eurocopter beans' wording at the start of this thread was 'known icing conditions' which is more specific then 'icing conditions'.

You interpret your RFM to read 'possible icing conditions' which I have no problem with but, just because you are in cloud below zero degrees, it doesn't mean that you will pick up ice because more often than not you don't.

check

21st Feb 2009, 07:53

Crab, your right, I never re-read the original post. However I still stand by my post.

We have three conditions available, no icing, icing conditions, and icing. The only way of being informed of known icing conditions are a) entering into the condition of flight in icing conditions where you may or may not pick up ice, or from reports from other aircraft that have done just that and picked up ice. If the met report reports icing then what's the question?

The wise will carefully read met reports and if icing conditions exist will ensure that if he/she decides to procede then they have to ensure enough space below to leave the icing and continue or return as the case may be.

This icing thing comes round every winter and most of us seem to handle it well, survival has something to do with it!

Xamlah

10th Feb 2010, 18:28

Hi guys,
I have been looking at the Bell 206BIII RFM and it says to turn on pitot heat and engine de-icing at OAT below 4.4 celsuis and visible moisture. Now, according to the manual flight is prohibited into 'known icing conditions'.

The questions that arise are:
1. What is visible moisture?
We have eyes for that, obviously and we know that mist, clouds, rain, snow and fog all are forms of visible moisture. There can also be an estimation of humid conditions by comparing the temp/dewpoint spread. I am looking for a specific definition, if any; as I have heard something related to visibility!
(I do not agree with having a definition when we have the word 'VISIBLE' in the manual)

2. What are known icing conditions?
Central Europe has icing conditions all winter. The zero-degree isotherm is always at SFC and icing conditions are always present. What would it be? PIREPs? AIREPs?
(To me its an area suspect-able to icing, like clouds, freezing rain or high altitude freezing areas)

Would really love to hear what other people have to say!
Thanks,
XR

paco

10th Feb 2010, 19:12

Visible moisture - what it says - mist, drizzle, hail, etc.

To the FAA, forecast icing conditions = known icing conditions. In court, in Europe, I suspect that known icing conditions would include where it could be reasonably expected that you would get icing, even if there wasn't a forecast to hand.

phil

ShyTorque

10th Feb 2010, 19:44

Known icing conditions are just that. If you fly and collect ice, that is known icing conditions. Some days the forecast can be incorrect, or just not accurate enough. A half a degree C can make the difference between collecting ice or not. You could change your track by a half a mile and be in (or out) of icing.

If the forecast indicates icing may take place, that should be used as a (strongly advisable) guide.

BTW, the engine has anti-icing protection, not de-icing. Anti-icing prevents ice formation. By definition, de-icing insinuates that you have already flown in icing and collected some ice.

Shawn Coyle

10th Feb 2010, 20:08

To add an importnt point. Anything larger than 0.5mm droplet size is freezing precipitation - and definitely must be avoided, even if you have an icing clearance.
A good rule of thumb for this is that if the moisture in the air is descending (as opposed to drifting around), then the droplet size is larger than 0.5mm.
Freezing mist is bad enough, freezing precipitation is much, much worse.

HeliComparator

10th Feb 2010, 20:43

Shawn, just to pick up on your point about freezing precipitation, I quite agree that flying in this stuff is a seriously bad idea, but I query whether its correct to say that no heli is cleared to fly in that stuff? There is nothing in the Eurocopter flight manuals about it (though flight in limited icing conditions is allowed with certain caveats). There used to be something in our Operations Manual prohibiting it, but its been lost along the way somewhere.

I have been asked about whether we can fly in freezing precipitation. Of course my answer is no, but I am at a loss to find written justification as to why!

So my question is, where does it specifically say that you can't fly in freezing precipitation? Or are you just taking the line that since it doesn't say you can, you can't.

I would also take the view that flight in snow or hail or ice crystal cloud is not icing conditions, provided the temperature is well below zero (if near zero, snow/hail can melt on impact and then re-freeze). In other words, if it doesn't stick it isn't icing conditions!

HC

aegir

11th Feb 2010, 07:58

As the question is "LEGALLY ice conditions" I think that we shall consider the ufficials forecast informations. IMHO

charlieDontSurf

11th Feb 2010, 10:16

WX.............: SCT SN/SNRA, LATE NIL CENTRAL PARTS,
RISK LCA FG/FZFG
VIS............: +10KM, LCA 2-7KM IN WX,LCA 0100-1000 M IN FG/FZFG
CLD............: FEW-SCT 1000-1500FT, SCT-BKN 1500-5000FT,
LCA BKN/VV 0800-1500FT IN WX,
LCA VV002-009 IN FG/FZFG
0-ISOTHERM.....: SFC-1000FT, BECMG SFC-2000FT
ICE............: FBL/MOD, LOC MOD, LATE BECMG FBL/NIL

This is from today's IGA prognosis at the western part of Norway.
It is forecast icing conditions, but we are still flying VFR ops with 350's. The crew reported light icing in snowshowers on the last trip, but went out again.
One has to fly in visible moisture to get ice, unless we talk about carb.ice. That's another story.
But if you push it, and hover in light fog in minus-degrees, you may get icing very quick! There have been a few accidents because of that.

One R-22 was doing run-up in light freezing fog, and when they were ready to depart, they couldn't get the heli in the air. They shut down again, and revealed a lot of ice on the blades.... What they were supposed to do, flying in freezing fog, is another question....:mad:

A 350 flew in -20 c in Northern Norway, blue skies. They were to drop of some workers in the bush, and there was light fog at the landingsite. They landed, let of the passengers, and took off again. They didn't get enough lift, and crashed a couple of hundred meters away. They got icing during the short ground stop.

We are very aware of the OAT during the winter when there's visible moisture. As some has pointed out, ice on the wipers is a good indicator.:)

Aucky

11th Feb 2010, 10:47

I agree with those who say airframe icing conditions are generalised as below 0 degrees Celsius and in less than 1Km viz (i.e. fog).

I have heard that the term 'visible moisture' by definition is moisture causing a visibility of less than 1Km, although i would be hesitant to fly in mist (1-4km) at less than 0 degrees, which incidentally i would say is quite visible :}

with regards to engine/carb icing, the temp drop across the carb can (i've heard) be as much as 30 degrees so in humid conditions one must be very careful not to get caught out flying in +30C....

also there is obviously the possibility of freezing rain under the passage of a warm front, if you're in the cold sector, and rain from the warmer sector above cools to below zero (supercooled) and sticks upon impact, or your airframe is very cold and fly's into the rain... leading to particularly dangerous clear ice. :eek:

Aucky

rotarywise

11th Feb 2010, 11:16

For what it's worth the CAA Supplement to the R22 POH says:

Icing conditions must be assumed to exist when in cloud, or when the visibility at takeoff is reduced to 1000 metres or less in visible moisture, with a true air temperature of 0°C or less. Icing conditions must also be assumed to exist whenever there are any visible signs of ice or slush build up on any part of the helicopter.

It goes on to state: Flight in freezing rain or freezing drizzle regardless of visibility is prohibited.

That'll do for me

Shawn Coyle

11th Feb 2010, 11:17

Helicomparator:
Like many things, it's not well defined. I know the Canadian FM for the Super Puma was amended to say No flight in freezing Precipitation, not sure about the others.
The logic is as follows:
The clearance for icing is based on testing to the requirements of one of the Appendices to Part 27 and Part 29 (can't remember which letter it is). This is the same wording and requirements as far as droplet size is concerned as the FW world uses. The maximum droplet size used for certification is 0.5mm, and anything larger is considered to be freezing precip. No one has a clearance to fly in freezing precipitation.
Hope that helps!

MightyGem

11th Feb 2010, 15:23

I have been asked about whether we can fly in freezing precipitation. Of course my answer is no, but I am at a loss to find written justification as to why!

Because, if you haven't realised from some of the posts, of the rapid buildup of ice on the airframe/rotors in freezing rain/drizzle. This leads to an increase in weight and power(to cope with the extra weight) and loss of a nice aerodynamic profile(and hence lift) on the rotor blades.

It's bad stuff: don't go there.

AOPA Online: In-Flight Emergencies: Avoiding ice fright (http://www.aopa.org/pilot/features/inflight9910.html)

Aircraft icing (xhtml w3c 11/09) (http://www.auf.asn.au/meteorology/section10.html)

Brilliant Stuff

12th Feb 2010, 19:31

More confusion.

I have it written down that the CAA in their publications believe Icing conditions are when the temperature is below +3°Celsius and visible moisture below 1500m sadly I can't put my finger onto the CAA document at the moment. Maybe after the weekend.

On the last page of the AS365 FLM it mentioned 4°Celsius if I remember correctly.

JohnDixson

13th Feb 2010, 12:53

Shawn, believe you are correct re the 50 micron droplet size being the max for icing certification.

HC, the problem with freezing rain is what has been called "runback", wherein the precipitation runs back beyond the aft limit of the de-icing system chordwise coverage and freezes there*. Creates both lift and pitching moment problems.
* In fact preventing runback from occurring within the normal icing conditions envelope is a major controlling factor in the de-icing element timing cycle development.

Thanks,
John Dixson

badger210

13th Feb 2010, 13:46

Some of you are probably aware of this but the standard weather service methodology and terminology used to characterize and classify the icing environment was developed from in-flight icing tests conducted on a Douglas DC4 and DC6 type aircraft. Thus labels such as trace icing, light icing, moderate icing and heavy icing related to the rate of ice accretion on a probe on a DC6, which does little to ascertain or predict the rate of ice accretion on a rotor system.
As an example, light icing is defined as an accumulation of one half inch of ice on a probe after 40 miles of flight. The rate of accretion is sufficient to create a hazard if flight is prolonged in these conditions, but insufficient to require a diversion.
The prior definition may well fit a large aircraft however there is no assurance that the rotating surfaces of a helicopter will accumulate only one half inch of ice over the same 40 miles, indeed there are many more factors in play with ice accretion to a rotor surface as opposed to a single non rotating airfoil that make it a much larger problem in much less time. Further while one half inch of ice on the wing of an airplane may correctly and appropriately be called “light icing” there is every reason to believe from testing that one half inch of ice on the leading edge of most helicopter rotor systems could result in tragic consequences if autorotation became necessary.

HeliComparator

13th Feb 2010, 14:43

Mightygem, JohnDixon et al

I guess I didn't make myself clear. In no way was I suggesting that flying in freezing precipitation was anything other than a very bad idea, and I am well aware of the seriously nasty effects that could rapidly arise if one foolishly did so.

My question only related to where in the legislation etc it is written down as being prohibited, so as to provide an answer to those that have asked me "but where does it say that?" when I have told them flying in FP is verboten.

HC

[email protected]

13th Feb 2010, 16:49

HC - my answer would be that you can't because there is no specific clearance to say you can. Since every pilot from day one is taught the dangers of freezing rain and drizzle it seems reasonable to argue that therefore being able to fly in it would require some special equipment and/or clearance. You can anti-ice your engines and you can de-ice your MR and TR blades (with the right fit) but to my knowledge there is no method of de-icing either the airframe or the pitch change mechanisms of the rotors, both of which will be badly affected by freezing precipitation.

I have only encountered freezing rain once and then only briefly but it was more than enough to convince me that all the warnings are valid.

It is always interesting to see which pilots go for 'I can do it because it doesn't say I can't' versus 'I can't do it because it doesn't say I can' when quoting rules and regulations.

malabo

18th Feb 2010, 17:29

HC, dug up some legislation wording used here in the great frozen north were nobody stops flying.

Transport Canada's latest position on freezing rain or drizzle is that it is equivalent to "severe icing". Quote from ASL 4/2009 "Takeoff into known freezing drizzle and/or light freezing rain is outside of the flight envelope for which any airplane currently operating today is certificated. ...".

Interestingly (or practically for operations in Canada), they differentiate between "forecast" icing, and "known" icing. In fact currently the regs 605.30 says
"no person shall conduct a takeoff or continue a flight where icing conditions are reported to exist or are forecast to be encountered along the route of flight unless
a) the pilot-in-command determines that the aircraft is adequately equipped to operate in icing conditions in accordance with the standards of airworthiness under which the type certificate for that aircraft was issued; or
b) current weather reports or pilot reports indicate that icing conditions no longer exist"

There is a proposal to change (b) further to permit more flexibility in operating in reported icing conditions:"b) current weather reports, pilot reports, or briefing information relied upon by the pilot-in-command indicate that the forecast icing conditions that otherwise prohibit flight will not be encountered during the flight because of changed weather conditions since the forecast." In other words, even if icing is forecast, if the commander has reason to believe his aircraft won't ice up along his route he can still fly.

So there you go for all you ice-dummy aircraft commanders. "heavy lies the crown..."

ShyTorque

18th Feb 2010, 18:58

My question only related to where in the legislation etc it is written down as being prohibited, so as to provide an answer to those that have asked me "but where does it say that?" when I have told them flying in FP is verboten.

Look in the RFM. ;)

400_Hertz

18th Feb 2010, 20:20

Water can remain liquid in 'icing conditions' i.e. below 0 deg C or 32 deg F but impact with an object (like a main rotor blade or airframe) can cause freezing into a solid. However, the "freezing" does not occur all-at-once. In fact, there is a substantial lag.

I expect you all know this already, it forms part of the knowledge associated with ice detection systems like the Leigh Ice Detector.

JohnDixson

18th Feb 2010, 21:20

HC, of course the RFM is the document as called out in 29.1581, but I suspect that you were getting at some of the definition arguments.

See the following for examples of the associated legal tangles:

The Naked Truth About Known Icing Conditions (http://www.avweb.com/news/airman/184265-1.html).

What fun.

Thanks,
John Dixson

HeliComparator

18th Feb 2010, 21:50

Crab:
HC - my answer would be that you can't because there is no specific clearance to say you can

In the EC225 flight manual it doesn't mention that its OK to do a spot turn. Does that mean I can't do one?

Shy:
Look in the RFM.
Good suggestion! But whilst the main part of the RFM says "flight in icing conditions prohibited", there is a Supplement that allow flight in limited icing conditions with specified equipment and caveats, however it doesn't say that flight in freezing precipitation is prohibited.

JohnDixon - it would be nice if the RFM covered this point but it doesn't...

HC

ShyTorque

18th Feb 2010, 22:58

I would class freezing precipitation as icing conditions (the worst sort).

[email protected]

19th Feb 2010, 06:49

HC - then you start to get into a rather fatuous argument like - does it say you can't fly backwards at 50kts? no, therefore it must be OK.

Spot turns are hardly a well documented, hazardous regime of flight (aklthough with some students I have had that might not be so) whereas flight in FP is. If your pilots want to go and fly in FP, let them and see what their viewpoint is when (if) they get back.

At some point you either have to force the manufacturer to amplify the limits in the RFM or, as you have done, make a clear policy decision not to fly in FP.

JohnDixson

19th Feb 2010, 17:35

HC and ShyTorque, A few years ago the FAA legal chaps wrote a response to the AOPA on this subject and in essence, referred them to the AIM, paragraph 7-1-22 and 23.

Not the clearest prose, but thats probably the best practical approach, because if one wants a complete technical definition, including liquid water content and droplet size, one would be asking for info not available in any met office briefing.

Thanks,
John Dixson

ShyTorque

19th Feb 2010, 19:02

Thanks John for the reference but I'm not familiar with the term "AIM" or where to find it. :confused:

birrddog

19th Feb 2010, 19:16

Shy, you can find it here
http://www.cksinfo.com/clipart/signssymbols/targets/Crosshairs.png (http://www.faa.gov/air_traffic/publications/ATpubs/AIM/chap7toc.htm)

;)

ShyTorque

19th Feb 2010, 20:43

Please accept my sincere graticule. ;)

sycamore

19th Feb 2010, 21:30

I posted some photos of flight in known icing conditions,that were taken between 1969-73,in Canada,in Sea-king,Wessex,Wasp and Gazelle icing trials.They`re on P 15 of `R/heads around the World,28 Nov `03. Trials were done in stratiform sub-0 cloud,with a good cloudbase,and heavily instrumented aircraft.

http://www.eacott.com.au/gallery/d/3362-1/icing+2.jpg
A Gazelle we did icing-trials with in Ottawa, 1976 Feb-Mar. We flew in everything from heavy snow to freezing rain, Spray-rig, and freezing fog. I see from my log book that I also spent most of the time with the hyd. off for control force measurements.

http://www.eacott.com.au/gallery/d/3364-1/icing+3.jpg
Ice-damage to a Wx/S-K engine(T-58/Gnome), which also illustrates why an axial-flow compressor with VIGV`s is not an ideal engine to use in a helo, without adequate intake protection.

http://www.eacott.com.au/gallery/d/3366-1/icing+4.jpg
A WX blade with ice :we used a max rise in Tq. of about 20-25 %, before you quit, IF you were not getting ice shedding naturally. That would still give you an acceptable rotor performance if both motors quit/or a trans. failure. Which did happen in a S-King-- Everyone had their chutes on, but they got back before the g/b seized.

http://www.eacott.com.au/gallery/d/3368-1/icing+5+cheyenne.jpg
AH-56A Cheyenne on an early rig-run.

http://www.eacott.com.au/gallery/d/3370-1/icing+7.jpg
Front shot of a Wasp blade, showing the stagnation-point at the L/E, and ice growing out above/below the blade; very dangerous as the rise in drag/ torque is very rapid.

Shawn Coyle

20th Feb 2010, 11:04

Sycamore:
Thanks very much for the pix. Great contribution! Send more.

A2B Ferry

28th Mar 2010, 09:59

Aircraft Icing Training - Courses (http://aircrafticing.grc.nasa.gov/courses.html)

All of your questions regarding icing are answered in the above link. Its a fantastic resource and its completely free. In short, if the SAT is between +2 and -20c and there is visible moisture in the atmosphere, then an airframe can accrete icing. The only limiting factor on the cold side is -40c. From a legal standpoint what are known icing conditions.? Well if you fly into visible moisture below the forecast freezing level, ie cloud, FZFG, FZRA, supercooled large droplets, ice pellets etc and your in a non de-iced aircraft and an accident results. The likely candidate who will inform you of the legalities would more than likely be your insurance company if you survive of course. Its also right as whirly mentions that snow isnt considered as icing conditions in flight (explained in the course relating to temp at which snow exists) but snow on an aircraft on the ground is a different issue and certainly would be considered a danger as snow insulates and a layer of snow on the aircraft on the ground could leave the airframe covered in a coating of ice. Any snow/ice should be removed prior to flight. I have known some people who thought, ah the snow will blow off when I start to roll? It most certainly would but what it left behind would certainly diminish the aerodynamic properties of said aircraft and the POH figures could be severely out.

nodrama

29th Mar 2010, 18:24

I'm looking for some information and informed experience on helicopter ice detection systems...

such as which ones are reliable, which ones aren't worth jack, how much warning they give you before the aerodynamic affects are noticeable.

Any info much appreciated.

A2B Ferry

29th Mar 2010, 20:50

YouTube - N1278L Icing Encounter.wmv (http://www.youtube.com/watch?v=ee0QsuLdnYg)

ee0QsuLdnYg

These are icing conditions and this is what happens when a full understanding of them arent met. And this aircraft was fully de-iced but a de iced aircraft in unskilled hands and the icing usually wins

Tazzz

10th Nov 2010, 02:58

Hello fellow Rotorheads.

Winter as arrived here in Europe. Ice formation is an old problem, but it continues to kill.

I never had to face it and would like to keep it that way, but if I have to face it it's best be be better informed to solve or avoid it the best way.

The only indication the most RFM gives besides not get in to the condition is to turn on the PITOT at 5 °C to 0ºC.
I can go through the clouds at temperaures very negative?

At what temperatures can not pass into the clouds. I've read the information from +5 ° C to 0 º C and also have read from 0 ° C to -10 º C. ..?

I wish that those who have some experience in the subject write here in the forum to better clarify this phenomenon, identification signs and solutions.

Thank you all in advance, and sorry about my English writing.

Safe Landings To All...

Non-PC Plod

10th Nov 2010, 11:13

Tazz,

There are engine icing conditions and airframe icing conditions. It is possible to get engine intake icing on some types well above zero (depends a lot on the intake design.) Likewise on the pitots, because of the pressure drop in the airflow around them, causing a reduction in the temperature from ambient.

Airframe icing will tend to start at one particular place for each airframe. Often the first place you will see it is on the wipers, the front of skids or antennae. You will have to ask around for the acquired knowledge on your particular aircraft. Airframe icing builds up fastest in temperatures close to zero, because of the size of droplets and the time it takes them to freeze as they run over the airframe. You can build up ice very quickly if you are in the wrong conditions, affecting the performance of your rotors (main and tail), affecting balance, aircraft weight, ability to autorotate etc. Shedding of ice from the rotors can damege other parts of the aircraft. In very cold weather, you may get less icing, but its best not to try it!

If your rotorcraft flight manual says to avoid icing conditions, then the best plan is to do just that. Dont fly where icing conditions are forecast - especially freezing rain. If you do enter icing conditions, turn round and get out again.
I knew a colleague when I was in the Navy who flew a Sea King into icing conditions. There was no way out (in cloud in mountainous region, no radar). They ended up pulling maximum contingency power at best rate of climb speed, and were still descending fast. They were lucky enough to exit the cloud at the base without hitting the ground , but it could easily have gone the other way!
Most helicopters dont like icing - very few have significant airframe/rotor icing protection. If you dont want to scare yourself, stay out of the clouds in Winter!

ObiWon

10th Nov 2010, 14:40

Icing conditions occur when your Wife's mother catches you in the rack with her other daughter.:D

topendtorque

15th Nov 2010, 11:35

here you go guys, something Mrs tet found in

Watts Up With That? (http://wattsupwiththat.com/)
one of the frequented blogs when we were fighting the warmists, also there is a substance the name of which totally eludes me now but it was around a few years ago for sure which you could spray on your motor car windscreen and it would disspate the rain drops very well allowing much less use of the wipers. If I can remember it I'll post the name.

cheers tet

Fighting ice at the nano level – a promise for improved safety (http://wattsupwiththat.com/2010/11/14/fighting-ice-at-the-nano-level-a-promise-for-improved-safety/)

Posted on November 14, 2010 (http://wattsupwiththat.com/2010/11/14/fighting-ice-at-the-nano-level-a-promise-for-improved-safety/) by Anthony Watts (http://wattsupwiththat.com/author/wattsupwiththat/)
This is a really neat discovery. As we all know, ice is a big killer and safety hazard, especially on airplanes (http://cloudman23.wordpress.com/tag/aircraft-icing/). This new material prevents supercooled droplets from freezing, sticking, and accumulating.- Anthony
http://cloudman23.files.wordpress.com/2009/02/icing-wing1.jpg?w=480&h=422&h=422
From Harvard: Breaking the ice before it begins (http://www.seas.harvard.edu/news-events/press-releases/breaking-the-ice-before-it-begins)
Nanostructured materials repel water droplets before they have a chance to freeze
http://wattsupwiththat.files.wordpress.com/2010/11/harvard_nano_ice.jpeg?w=640&h=168 (http://wattsupwiththat.files.wordpress.com/2010/11/harvard_nano_ice.jpeg) Sequential images of ice layer removal from hydrophilic Al, fluorinated hydrophobic Si, and microstructured fluorinated Si (SHS). Note the supercooled droplet bounces right off without sticking.

Cambridge, Mass., November 12, 2010 – Engineers from Harvard University have designed and demonstrated ice-free nanostructured materials that literally repel water droplets before they even have the chance to freeze.
The finding, reported online in ACS Nano on November 9th, could lead to a new way to keep airplane wings, buildings, powerlines, and even entire highways free of ice during the worst winter weather. Moreover, integrating anti-ice technology right into a material is more efficient and sustainable than conventional solutions like chemical sprays, salt, and heating.
Continue reading → (http://wattsupwiththat.com/2010/11/14/fighting-ice-at-the-nano-level-a-promise-for-improved-safety/#more-27802)

Posted in Science (http://en.wordpress.com/tag/science/), Technology (http://en.wordpress.com/tag/technology/), weather (http://en.wordpress.com/tag/weather/) | 49 Comments (http://wattsupwiththat.com/2010/11/14/fighting-ice-at-the-nano-level-a-promise-for-improved-safety/#comments)

Brilliant Stuff

16th Nov 2010, 02:07

Do you mean Rain X ?

That aeroplane looks scary. I can't believe it is still generating lift with all of that on.

topendtorque

19th Nov 2010, 10:41

Do you mean Rain X ?

yes I think so.

Brilliant Stuff

28th Nov 2010, 22:31

AIC 118/2006 (Pink 106) 5.1 (http://www.nats-uk.ead-it.com/aip/current/aic/EG_Circ_2006_P_118_en.pdf)

This AIC will give you the CAA definition of Freezing +3°C < 1500m Viz.

I hope it helps.

newfieboy

29th Nov 2010, 01:12

Mmmm,

Come to Canada, if you can;t figure icing conditions this time of year, theres no hope......been in it all day, on a longline, you start picking up ice, you land, wait 10 mins, then go again when it clears up....easy...:DStill got 6.2 in and thats 8hrs of daylight.....:ok:

Bladestrike

29th Nov 2010, 10:35

"I'm looking for some information and informed experience on helicopter ice detection systems...

such as which ones are reliable, which ones aren't worth jack, how much warning they give you before the aerodynamic affects are noticeable.

Any info much appreciated."

I'm flying Super Pumas certified for flight in known icing on Canada's East coast, but flight in severe icing is prohibited, which we consider any freezing precip.

As far as detectors I've flown with many of them and none seem to work, giving warnings in clear blue sky and no warnings when we have inches of the stuff on us. The best indicators are the mirrors and wipers, and of course the torque, which will initially climb about 3 to 4 percent if you neglected to put the kit on for any reason. Having flown S61's out here at night for years watching for that torque rise (we would not go out in known icing of course, but forecasting being what it is, you sometimes encountered cloud below zero you couldn't see at night) I must say a certified for flight in icing aircraft reduces my daily stress considerably.

MarSch

5th Jan 2018, 16:54

Hello sycamore,
at the moment, I'm writing my PhD-Thesis, and would like to use one of your images showing iced rotor blades, you posted in #48 in the introduction of my work.
Are these your private images, or where did you get them from? If they're your images, do you allow me to re-use them or one of them in my thesis?
Kind regards,
MarSch

JohnDixson

6th Jan 2018, 17:06

Mar you might check:

1, SAE Paper 2003-01-2093 authored by Robert Fleming that traces the technical story of developing the UH-60 from a design point of view.
2. Also worth looking up the US Army Flight Test reports on their sequential icing flight tests with succeeding versions/configurations of the UH-60.

In all of these, you will see that both design engineers and flight test engineers/test pilots were well aware of the impact of droplet size/temp.

Have at it.

MarSch

6th Jan 2018, 19:52

Thank you very much for your answer, John.
I'm not searching for detailed studies, since I already have many papers (including those of R. Flemming) about ice accretion in my library. I'm only searching for an image to illustrate ice accretion in the context of rotorcraft in the motivation of my work. However, any of the publications in my library contains photographs of a quality comparable to those in sycamore's post. Therefore, I hope that sycamore will reply to provide information of the origin of the posted photographs.
Regards, MarSch

JohnDixson

6th Jan 2018, 20:44

The US Army Flight test reports are replete with very good photos. Since you are doing a doctoral thesis, you might write or phone them and obtain some copies of the originals. That test organization is now located at Ft Rucker AL

sycamore

6th Jan 2018, 21:17

MarSch,thank you for the compliment vis the photos;most were taken by one of the engineers,responsible for the multitude of instrumentation that we had fitted to each of the aircraft,when I was a T-P at AAEE Boscombe Down,when we first began to do serious ice/snow/freezing rain trials in Canada and Norway,over many winters.
It should be remembered that all our helos of the time used the same blade section NACA0012,a fairly conservative symmetrical section,whereas now blade sections are much more exotic and may well not give similar results.
You probably know about the NRC Spray rig ,and snow blower in Ottawa(gone now) that we used to initially establish some basic icing flying in the hover and covering a variety of temperatures and water droplet size and flow rates,and see if the ice would `self-shed`,in low altitude forward flight,or not!! Also the effects on the engine/intake configuration,and whether heating them or leaving `cold` would be beneficial.
We would then go into cloud,picking a time/day when there was a stratiform cloud layer,hopefully at a suitable base altitude of 2-3000ft,,and then `nibble` into the cloudbase for a short period to then drop out,then back in again,repeating as necessary until we reached a limiting torque rise,if there was no noticeable ice shedding,or if it could be induced in turns ,etc.We also had various detectors to calibrate ice accretion,temperature,droplet size and flow/mass rate,and the information would be correlated with the spray-rig.We did suffer engine problem with damage to the Wessex5 engines due to the small clearances between the Inlet Guide vanes and the compressor blades.This was later modified by fitting modified Sea-King IGVs to the first 2-3 stages in the compressor.We also had `mushroom` intakes fitted to the Sea-King( like all Russian MiL helos).
I suggest you use the photos with a credit to AAEE anyway,as I`m not certain which I may have taken anyway.
In retrospect the only way is to have fully automatically controlled blade
de/anti-icing,and engines that have a centifugal compressor/fan as the first stage,like the Astazou in the Gazelle and Nimbus in the Wasp/Scout..
Testing in icing conditions is a long and tedious job,and one can always be `bitten`...!!
I wish you well with your thesis,and happy to answer further,bearing in mind we were doing this 40+ years ago,,,but icing is still there..
Rgds,Syc

MarSch

7th Jan 2018, 10:31

@ John: Thank you again for your hint regarding US Army flight testing. Unfortunately, I didn't find an appropriate photograph in their reports in the web. Therefore, I wrote an e-mail to Fort Rucker, asking for some pictures and permission to use them.
@ scy: Thank you very much for your detailed description of the conditions and procedure during testing. I've noticed that AAEE Boscombe down doesn't exist anymore. However, I'm not sure about the rights to use their images. Thus, I've contacted the British Ministery of Defence hoping they may provide information about the rights-holder of the photographs.

Anyways, thanks again to both of you for your help.
Finally, I've got a rather simple question: Are you still in business or already retired?

Kind regards,
MarSch