Freezing Rain

[AltFlaps]

Hi All,

Other than the normal in-flight and pre departure de-icing and holdover limits, do any of you have additional company restrictions on operating in Freezing Rain ?

If so, what aircraft types?

Thanks

AF

[rubik101]

If the flight conditions are such that you are experiencing anything more than light to moderate icing then you are flying outside the limitations of 'all' aircraft types.
If the freezing rain causes heavy ice then you had better turn around or get in out of the rain asap.

[AltFlaps]

Thanks Rubik,

But I'm trying to find out if any operators have specific limitations with regard to Freezing Rain ... I've heard that some airlines specifically prohibit operation in known freezing rain conditions

AF

[wacky]

Flybe forbid it, as did BAConnect etc beforehand. Company policy for all types.

Neither a take-off nor an approach and landing is to be carried out in actual freezing rain or freezing drizzle conditions. In practice this implies:
a. Before departure if the destination is actual, or forecast to have, freezing rain or freezing drizzle then two alternates must have landing minima and no freezing rain or freezing drizzle.
b. If, when airborne, the ATIS gives freezing rain or freezing drizzle then no
approach can be made to that airport until the condition has cleared.
c. A take-off is not permitted during reported freezing rain or freezing drizzle

[Admiral346]

A takeoff is simply not possible for anyone, because no holdovertimes exist for freezing rain (they do for FZDZ). You would have to depart with ice on your wings (most likely prohibited by your SOPs) or without a holdover time (against all SOPs known to me).

Nic

[Swedish Steve]

Other than the normal in-flight and pre departure de-icing and holdover limits
Have you looked at the deice hold over times? Even 100pc type 11 can give you as little as 5 mins holdover. This is counted from start of deicing. Can't be done safely.

[rubik101]

Alt Flaps, if you are looking for someone to post on here that they work for an airline which allows operation in freezing rain, forget it. It is not allowed, under any circumstances.
End of discussion.

[topjetboy]

Under Canadian regs, Type IV allows operation in -FZRA down to -10 with a holdover bracket of 10-20mins. Or, if it's warmer, as much as 40mins!
The FOM specifically allows us to plan to, and operate in -FZRA.
Unlucky Rubik.

[rubik101]

Thank goodness I don't fly to Canadian regs. What a bunch of tossers if they allow such lunacy. You will surely die if you try to fly in freezing rain, no question.
I say again: Just don't do it.

[Intruder]

There is a difference between LIGHT Freezing Rain and Freezing Rain. AFAIK, no operator allows attempted takeoff in Freezing Rain, for the reasons already stated above. However, some do allow takeoff in LIGHT Freezing Rain or Freezing Drizzle, if holdover times allow and visual inspection is successfully accomplished immediately prior to takeoff.

[just.n.av8r]

FAA holdover allowed for light freezing rain as well.

Stupid Yanks, between them and the Canucks it is a good thing they don't fly in much weather.

[secret agent 86]

Being ignorant of a topic is not a reason to call people tossers. The simple fact is that in the Great Lakes and Eastern Seaboard region of North America, freezing precipitation of some sort is a fact of life in winter and if all aviation were to shut down then chaos would ensue. By following established guidelines, operations in freezing precip can and is safely carried out.

[Pugilistic Animus]

Stupid Yanks, between them and the Canucks it is a good thing they don't fly in much weather.


yeah right:rolleyes:

we are known have the world worst wx supercells, squall lines, tornadoes mesoscale convective TS, mountain wave activity, hurricanes, freezing precip., hail, as well as plenty of interesting terrain

[indiscipline_girl]

I lived and flew airplanes in alaska before. The single most hazardous weather event was freezing rain. Even just driving cars, I was stuck in traffic for 3 hours because the entire highway turned into an ice rink within minutes (near eagle river for those in the know).

Freezing rain is GOD's way of ruining your plans for the day.

[porch monkey]

I guess the sarcasm was lost on you P.A.?

[just.n.av8r]

P.A.,

Sorry my sarcasm wasn't clear.

BTW, worst freezin rain I ever experienced was in North Carolina, not Alaska.

[Pugilistic Animus]

Just.n.av8r
Worst freezing rain I ever experienced was in North Carolina, not Alaska.
RDU? usually a nice place
I'm an ass:O

I guess it's best to fly in the part of the US where the humuhumunukunukuapuaa go swimming by:}

[Mansfield]

I have been involved in the issues of inflight icing for a number of years, both as a USALPA representative and an independent consultant. In the course of that work, I developed an icing database from a review of all US icing accidents and reportable incidents from 1978 through 2006. The latest iteration of this work was a presentation to the SAE at Seville in September of 2007, and can be seen at this URL:

http://www.sae.org/events/icing/presentations/2007s30green.pdf

Unfortunately, this online PDF has some problems with some of the charts; I'd be glad to send a cleaner copy to anyone interested.

One outcome of the work was based on normalizing the frequency of surface precipitation reports with the events in the database. 32% of the events were associated with snow, and snow comprised 32% of the surface precipitation reports in the continental United States. However, 33% of the events were associated with either ZR or ZL, which comprised only 1.8% of the total surface precipitation reports.

The majority of this data involves non-transport certificated aircraft.

It would be a mistake to assume that snow is safer, as seen by the large number of icing events that take place in the presence of snow. While the snow itself does not generate an ice accretion, it is often mixed with supercooled liquid water, which does. But the high frequency of events associated with freezing precipitation, compared to it's relative low occurrence rate, is an indication of it's vicious nature in the world of aerodynamics.

Indeed, there are not as yet any certification criteria or standards for conditions known as Supercooled Large Droplets (SLD) which we define as droplets with a median diameter of more than 50 microns. Thus, no aircraft are equipped with ice protection systems that have been designed or certificated for these conditions. This is in stark contrast to the existing holdover tables, which do allow operation in light ZR and light to moderate ZL. The dichotomy has kept a number of people in the authorities very busy, and very frustrated, for several years now.

[just.n.av8r]

My airline's FAA approved specific limitation prohibits flight into greater than light freezing rain and they provide us with FAA approved holdover tables for light freezing rain.

From that information I imply that operations in light freezing rain are permitted with appropriate procedures and precautions.

[che ci dò che ci dò!]

"... certification standards provide protection for the majority of atmospheric conditions encountered, but not for freezing rain or freezing drizzle or for conditions with a mixture of supercooled droplets and snow or ice particles...."


does any of you know in which part of JAR 25 one can find the above mentioned limitation? I couldn't find it.

Thanks

[hetfield]

In Italy, do you fly if it's raining?

[Mansfield]

The certification requirements for icing are in CS 25.1419. This will refer you to Appendix C, which gives the engineering standards for icing.

Figures 1 and 4 of Appendix C will detail the envelopes. Note that the x-axis shows mean effective droplet diameter. For the continuous maximum condition in Figure 1, the envelope ends at 40 microns. For the continuous intermittant condition in Figure 4, it ends at 50 microns.

The World Meteorological Organization defines freezing drizzle as droplets of 0.2 to 0.5 millimeters in diameter, and freezing rain as 0.5 millimeters and above. Supercooled Large Droplets (SLD) are defined as droplets larger than 50 microns, or 0.05 millimeters.

So ZL and ZR exceed the envelopes specified in Appendix C. These envelopes are not true certification standards, but rather engineering standards used to define a representative condition. This allows the manufacturers to argue that certification under Appendix C does not prohibit operation in ZL/ZR, and this is how the FAA Flight Standards Service issues Operations Specifications which allow takeoff in light ZR, etc. However, the FAA Aircraft Certification Service has taken the opposite position for several years. They do not believe that aircraft should operate in conditions which so obviously exceed the design parameters generally used.

[Mad (Flt) Scientist]

"... certification standards provide protection for the majority of atmospheric conditions encountered, but not for freezing rain or freezing drizzle or for conditions with a mixture of supercooled droplets and snow or ice particles...."

does any of you know in which part of JAR 25 one can find the above mentioned limitation? I couldn't find it.

Thanks

I think you'll find Appendix C quite enlightening.

14 CFR 25 App C (http://ecfr.gpoaccess.gov/cgi/t/text/text-idx?c=ecfr&sid=f2369b76c70442277dd33fe92cdae89d&rgn=div9&view=text&node=14:1.0.1.3.11.8.201.18.18&idno=14) is basically harmonised, and available online.

Generally, most kinds of freezing rain (and indeed SLD also) lie outside the defined limits for continuous maximum and intermittent maximum icing in Part I. Since this is what defines the icing certification under 25.1419 etc., it follows that it's outside the cert limits for any aircraft.

Appendix "X", still under development, is supposed to define icing conditions outside the App C. envelopes. Don't hold your breathe.

[BelArgUSA]

I vaguely recall most FAA certificated airplanes to be able to handle light/moderate icing only.
Lots of dust in my CAR 4b and FAR 25 pages...
xxx
However would mention that the L-188 Electra could handle "heavy icing".
At least is what I recall vaguely from a classroom discussion 35+ years ago.

Maybe our illustrious 411A can clarify the certification of the superior Lockheed product.
:E
Happy contrails

[Mad (Flt) Scientist]

I vaguely recall most FAA certificated airplanes to be able to handle light/moderate icing only.
Lots of dust in my CAR 4b and FAR 25 pages...
xxx
However would mention that the L-188 Electra could handle "heavy icing".
At least is what I recall vaguely from a classroom discussion 35+ years ago.

Maybe our illustrious 411A can clarify the certification of the superior Lockheed product.
:E
Happy contrails

Nope.

By definition, NO a/c can handle "heavy" (or. "severe") icing because it's defined as aircraft specific, and heavy is when it overpowers whatever anti-/de-ice systems you have.
Severe icing: The rate of accumulation is such that deicing/anti-icing equipment fails to reduce or control the hazard. Immediate flight diversion is necessary

But the light/moderate/heavy/severe is a subjective, aircraft-dependent scale, and not directly related to actual LWC etc. conditions.

See here (http://www.tc.faa.gov/its/worldpac/techrpt/ar01-91.pdf) fo a discussion on the terminology.

[safetypee]

PKPF68-77, the UK AIP section3, para 3.3 (www.nats-uk.ead-it.com/aip/current/gen/EG_GEN_3_5_en.pdf) defines icing and notes:

“It should be noted that the following icing intensity criteria are reporting definitions; they are not necessarily the same as forecasting definitions because reporting definitions are related to aircraft type and to the ice protection equipment installed, and do not involve cloud characteristics. For similar reasons, aircraft icing certification criteria might differ from reporting and/or forecasting criteria.”

Another gap between certification and operational views – opportunity for error.

[Ex Cargo Clown]

Interestingly the TAF for BFS tonight shows

TAF EGAA 041101Z 0412/0512 34004KT 9999 FEW018 SCT035 PROB30
TEMPO 0412/0417 8000
TEMPO 0417/0422 7000
TEMPO 0422/0507 8000 -RADZ -RASN BKN012 PROB30
TEMPO 0423/0506 7000 FZRA BKN009

Not often you see mention of FZRA on UK METARs. Even if it is only PROB30

[Canadapilot]

...meanwhile the whole of Canada had a white Xmas for the first time in 35 years, and December was one of the coldest, snowiest months on record. Global warming my arse! As an Englishman living in cold Alberta it does humour me to read British press forecasting "blizzards", "arctic weather" and "frigid temperatures"...i guess it's all subjective!

[Mansfield]

With regard to the Ozark DC-9 accident at Sioux City, and the straight vs. swept wing argument, consider this accident summary:

Feb. 16, 1950 • Douglas DC-3 • Eastern Airlines • Lexington,
Kentucky, U.S. • Injuries: 18 minor or none
During letdown into Lexington, ice accreted on the leading
edges of the aircraft’s wings and on the propeller blades. To
offset the reduced effectiveness of the wings and propellers,
the pilot increased airspeed on his approach. After the aircraft
landed without incident, only the left engine was secured for
ramp loading operations. No action was taken to remove ice
from the aircraft.

When ramp loading was completed, the aircraft took off again.
It stalled shortly after it became airborne, and the pilot was
unable to regain control. The aircraft touched down, rolled
through a gully and came to rest in normal landing attitude.
Damage to the aircraft was substantial.

As I pointed out in another thread, the lift curve with a thin coating of roughness on the leading edge very often overlays the clean wing lift curve, up to a point. The stall will often occur abruptly at an angle of attack several degrees below that of the clean wing. When someone speaks of a wing "handling" any amount of ice, that simply means that they have not had occasion to attempt an angle of attack greater than the contaminated lift curve will allow. However, ANY contamination absolutely guarantees that the wing will not provide the same performance across its intended range of angles of attack. It doesn't matter whether it is straight, swept, slatted, fat or thin...you simply don't know where the lift curve is going to go off a cliff.

[AltFlaps]

Thanks for the info everyone ... I guessed it would more than simple ...

And by the way, rubik101, you're knob jockey ! :ok:

Thanks again

[Taxi2parking]

Bit harsh on Rubik101 .....maybe he is struggling with the concept of a regulation which means that the crew have to make the assesment as to when those supercooled droplets, coating anything that moves (or otherwise), are in fact light or medium freezing rain.:eek:

Very sensibly our company's Part A makes a clear statement that we are not to operate in freezing precipitation. In fact they even removed -FZRA from the published holdover tables. That avoids some poor fool making a bad call as to whether it's light or medium, under the inevitable commercial pressure, when he is trying to decide if he should give it a crack.......

[flipster]

Lots of mentions of FZRA and FZDZ but what about FZFG - surely that is made of supercooled water droplets as well? Or are they too small (less than 50 microns???).

My recollection, however, is that they cause icing too, or am I being dull (ops normal)?

flip

[Taxi2parking]

Hey flip - I'll would check next time I'm in moscow but my micrometer is at the menders.

I don't think freezing fog is such an issue - as you say the drops are not large enough to fall under their own weight and won't lead to severe icing. Isn't it something to do with the droplets have to be a certain size to release enough latent heat to produce clear ice rather than rime ice when it strikes the airframe?...or something like that:p

is life still orange for you?

[A-3TWENTY]

Good Question...FZFG...I don`t know either....

[Admiral346]

FZFG is encountered at MUC, my homebase, often during the wintermonths. It can be handled easily. You get deiced right before takeoff, and after the 40 sec to Vr, you spend maybe antoher 20-30s until you pop out of the low stratus into sunshine with unlimited view into the Alps - a beautiful day to go skiing were I not sitting there with a jet strapped onto my back...

But FZRA, now that is a totally different matter. I have read the SLD discussion years ago, as it was published by the safety department of our company. I do believe you are operating outside the certification limits - and I have made it my personal limit on how far I am willing to go, how much risk I will take, to hell with all regulations.

I won't even let my wife drive to the supermarket in case of FZRA!

Nic

edit: I don'T know the scientific explanation, just the results...

FZFG is what causes rime on trees, looking oh so pretty once the fog clears out and the sun shines - on aircraft it causes rime ice, slowly.

FZRA leaves a blanket of clear ice on anything it touches - wings, rwys, streets, sidewalks - see the picture above - I would call that heavy ice...


edited to say: In FZFG fanblade icing can be a problem, watch out and do run ups as required...

[flipster]

Aha! That all sounds most logical... I think! - thanks all.

It was interesting to note that the head of Royal Metrological Society was on BBC Radio 5 today, talking about the risk of FZDZ in the UK this pm but, when I left the crewroom at about 1900, there had been no mention of it in any of the UK TAFs nor Sig Wx charts (there was a bit of FZFG in the London TMA but no FZRA or FZDZ, tho' I think FZRA had been reported at AMS and RTM). This seems strange when the met man was quite specific about FZDZ and clear ice?

Did anyone have any encounters/reports/experience?

Any met men care to explain it all to this thickie pilot?

flip


taxy2pkg - nope, am at SOU now.

[Admiral346]

Here is a scientific explanation of FZRA, done quite well:

Freezing Rain: supercooled droplets freezing on impact (http://ww2010.atmos.uiuc.edu/%28Gh%29/guides/mtr/cld/prcp/zr/frz.rxml)

I wasn't so lucky on finding anything on FZFG, more of a simple explanation:

BBC - Weather Centre - Features - Understanding Weather - Fog (http://www.bbc.co.uk/weather/features/understanding/fog.shtml)


Nic

edit: You want this on your aircraft?:

YouTube - Austin, Tx...Ice Storm '07 (http://de.youtube.com/watch?v=3L4BrZDwt7k)

[JW411]

I flew into FZRA one night between Malta and Cyprus. Despite an immediate 180 degree turn and application of MCT, we stabilised at just a few thousand feet above the Mediterranean and the aeroplane looked like a Christmas tree.

Ever since then, every time I see FZRA on my met sheet, I go back to the crewroom.

I don't really care what all the fancy books say!

[rubik101]

Altflaps, just what do you mean by knob jockey?
Taxi 2 parking, just what concept is it that you think I was having trouble with?
Just where did I suggest that flying in anything other than light freezing rain was permitted?

[Jetset320]

Several diversions from Frankfurt this morning, apparently due to light freezing rain, yet on the other hand not as many as you'd expect. So my guess is that many landed and the ones who diverted are not permitted by SOPs. Should there be one common safety take on this?

This is the weather Frankfurt was having this morning:

EDDF 240750Z 05005KT 3400 -SN BR SCT003 BKN018 M01/M03 Q1024 TEMPO 3000 BKN012=
EDDF 240720Z 06005KT 4500 -FZRA -PL BR OVC019 M01/M03 Q1023 TEMPO BKN012=
EDDF 240650Z 06005KT 9000 -FZRA OVC019 M01/M04 Q1023 NOSIG=
EDDF 240620Z 06005KT 9999 OVC019 M01/M04 Q1023 TEMPO -FZRA=
EDDF 240550Z 06005KT 9999 OVC019 M01/M04 Q1023 TEMPO -FZRA=

[FEHERTO]

It is interesting to hear, how people are differnet interpreting the hold-over-time and weather conditions:

1. The tables of FAA, Transport Canada and Association of European Airlines (use most in the world) are absolutely identicial for these weather categories. So none of them is stupid or all of them.

2. Please be more precise: Absolutely no hold-over-time exists for moderate or heavy freezing rain. But some tiems exists for light freezing rain and freezing drizzle.

3. the given times for these weather conditions are very short. So only if you make the treatment directly at the runway with runnign engines you have a chance.

4. The whole tables are questionable, as they are based only on a few datapoints and for my opinionm not enough substantiated. But at the moment nothign better available.

5. My experience is, being of of these "idiots" involved in the development of these tables, that the most people are simply not properly trained to understand them. they are not easy to read with all the cautions and notes, but the airlines are not spending enough time.

If you want to get a punch of good information free of charge, go and register as a "Mail Recipient" with the SAE G12 Committee. Or better attend and help to improve it.

Just calling everybody else here, like some of you do, idiots, shows only that you have a problemto understand these tables and weather conditions.

[LEM]

I had an argument once about this: it was raining, end the reported temperature was 0°C.

There was absolutely no sign of a layer of ice being formed on anything. Just raining normally.

Would you define that Freezing Rain?

I think the definition implies the actual forming of a (thin) layer of ice on objects exposed to freezing rain.

:confused:

[FEHERTO]

Freezing Rain (and Freezing Drizzle) have the "freezing factor" (coldness) in the transported liquid.

If the OAT is at or above 0° C and the rain freezes than we talk about "rain on cold soaked wing", which is a seprate category in the hold-over-time tables and gives the shortest protection at all.

Looking into incident statistics, "Rain on cold soaked wings" is the most critical one, as a lot of ground and flight crews completely ignore the fact of a cold wing. Otherwise, how you can explain that we still have engine FOD's by clear ice after identifying the problem 25 years ago.

Finnair did a few years ago a study on the wing temperature durign the take-off run and take-off. The result had been that in the lift-off face the wing temperature drops dramatically. This fatcor must be taken additonally into consideration.

Looking on the existing test data, the accident and incident statistics as well as from my own experience:
- No hold-over-time for Type I Fluids at all, except in "Active Frost"
- Deletion of the 3° buffer for Type I Fluids in a Two-Step Procedure
- Starting the project to install temperature probes in the wings to get more precise information about the wing temperature