Freezing Rain
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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.
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.
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"... 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
does any of you know in which part of JAR 25 one can find the above mentioned limitation? I couldn't find it.
Thanks
14 CFR 25 App C 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.
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Ice cubes for my whisky...?
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.
Happy contrails
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.
Happy contrails
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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.
Happy contrails
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.
Happy contrails
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
See here fo a discussion on the terminology.
PKPF68-77, the UK AIP section3, para 3.3 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.
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.
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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
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
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...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!
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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 aircrafts 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.
Kentucky, U.S. Injuries: 18 minor or none
During letdown into Lexington, ice accreted on the leading
edges of the aircrafts 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.
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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.
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.......
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.......
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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
My recollection, however, is that they cause icing too, or am I being dull (ops normal)?
flip
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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
is life still orange for you?
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
is life still orange for you?
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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...
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...
Last edited by Admiral346; 2nd Feb 2009 at 21:15.
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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.
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.
Last edited by flipster; 2nd Feb 2009 at 21:33.
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Here is a scientific explanation of FZRA, done quite well:
Freezing Rain: supercooled droplets freezing on impact
I wasn't so lucky on finding anything on FZFG, more of a simple explanation:
BBC - Weather Centre - Features - Understanding Weather - Fog
Nic
edit: You want this on your aircraft?:
YouTube - Austin, Tx...Ice Storm '07
Freezing Rain: supercooled droplets freezing on impact
I wasn't so lucky on finding anything on FZFG, more of a simple explanation:
BBC - Weather Centre - Features - Understanding Weather - Fog
Nic
edit: You want this on your aircraft?:
YouTube - Austin, Tx...Ice Storm '07
Last edited by Admiral346; 3rd Feb 2009 at 10:08.
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!
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!
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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?
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?
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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=
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=