Icing in R/W Aircraft
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Icing in R/W Aircraft
Hello,
I have some questions about flight in and around conditions favorable to icing. I did a couple searches and didn't turn up quite what I was looking for.
The situation is this: I have a little time in cold areas, but in a helicopter with Blade De-ice equipment. In my time there I noticed that being in the clouds at 3C and below doesn't always lead to icing. I understand that this has a lot to do with the water content of the clouds, Temp, pressure, etc. I just didn't have enough time up there to make meaningful conclusions regarding what indicators (besides the ice-rate meter) would predict a lack of ice, even when the temps and presence of clouds indicate there should be ice. My question, really, is this:
If I am flying an aircraft NOT approved for flight into known icing conditions, are there any times I would be able to (prudently) fly in IMC conditions when the temps are conducive to icing? Does anyone here have extensive helo cold wx ops experience who could offer some experience based advice?
I just had another pilot in our program say, "Well, the tops are forecast only up to 8,000ft. Just get on top." Our program is based at 1000ft, which means with ceilings at 1000ft, we would be flying through the clouds for 6000 feet, (BEST case, 6 minutes) a with a temp/DP of M05/M07 at the surface. Seems to me like that would be a good time to pick up some ice.
Thanks for the help,
Scott
I have some questions about flight in and around conditions favorable to icing. I did a couple searches and didn't turn up quite what I was looking for.
The situation is this: I have a little time in cold areas, but in a helicopter with Blade De-ice equipment. In my time there I noticed that being in the clouds at 3C and below doesn't always lead to icing. I understand that this has a lot to do with the water content of the clouds, Temp, pressure, etc. I just didn't have enough time up there to make meaningful conclusions regarding what indicators (besides the ice-rate meter) would predict a lack of ice, even when the temps and presence of clouds indicate there should be ice. My question, really, is this:
If I am flying an aircraft NOT approved for flight into known icing conditions, are there any times I would be able to (prudently) fly in IMC conditions when the temps are conducive to icing? Does anyone here have extensive helo cold wx ops experience who could offer some experience based advice?
I just had another pilot in our program say, "Well, the tops are forecast only up to 8,000ft. Just get on top." Our program is based at 1000ft, which means with ceilings at 1000ft, we would be flying through the clouds for 6000 feet, (BEST case, 6 minutes) a with a temp/DP of M05/M07 at the surface. Seems to me like that would be a good time to pick up some ice.
Thanks for the help,
Scott
Seems to me like that would be a good time to pick up some ice.
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i guess you first have to play with the semantics of "filght into known icing conditions"
a) do you think it means forecast or actual ?
b) do you think it means conditions that are condusive to icing ?
you have answered your question if you follow b)
if there is no forecast for icing, but the conditions for it exist --forecasts can change--- (usually as you lift off).
so, sorry if i've responded to your post with no experience with flight in the situation you proposed, because i would stay out of the cloud.
a) do you think it means forecast or actual ?
b) do you think it means conditions that are condusive to icing ?
you have answered your question if you follow b)
if there is no forecast for icing, but the conditions for it exist --forecasts can change--- (usually as you lift off).
so, sorry if i've responded to your post with no experience with flight in the situation you proposed, because i would stay out of the cloud.
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Icing Conditions
Hi,
For our helicopter which has engine intake anti-icing but no blade anti-icing, we use the definition of icing conditions as temp below 0 degrees and visibility less than 1000m due to cloud/fog or precipitation. Snow is not included and has it's own limits, because it's less sticky.
You say that your heli is not cleared to fly in icing conditions, therefore I doubt you'd be able to justify flying in icing conditions. Also consider how accurate your OAT gauge is (ours only to 1degree), whether your engine will be subject to icing problems in air warmer than zero because of low pressure at the intake raising the freezing temperature of the water vapour. This is probably why you thought you were in icing conditions before at 3degrees but didn't see any ice: there shouldn't be any airframe ice but you may get some in the engine intakes.
There should be something from the manufacturer about all these limits. My heli (Lynx) has very complex icing limits, in order to make them as flexible as possible. I flew the Squirrel before and it was a "no flight in icing conditions" job.
I assume that you know all about the effects of icing on a helicopter. They can all be quite severe, especially in one not designed to cope.
I'm sure that a good book on helicopter ops (sorry I don't know if they exist because I get my stuff free and complicated from HM) would have all this in.
Yours
For our helicopter which has engine intake anti-icing but no blade anti-icing, we use the definition of icing conditions as temp below 0 degrees and visibility less than 1000m due to cloud/fog or precipitation. Snow is not included and has it's own limits, because it's less sticky.
You say that your heli is not cleared to fly in icing conditions, therefore I doubt you'd be able to justify flying in icing conditions. Also consider how accurate your OAT gauge is (ours only to 1degree), whether your engine will be subject to icing problems in air warmer than zero because of low pressure at the intake raising the freezing temperature of the water vapour. This is probably why you thought you were in icing conditions before at 3degrees but didn't see any ice: there shouldn't be any airframe ice but you may get some in the engine intakes.
There should be something from the manufacturer about all these limits. My heli (Lynx) has very complex icing limits, in order to make them as flexible as possible. I flew the Squirrel before and it was a "no flight in icing conditions" job.
I assume that you know all about the effects of icing on a helicopter. They can all be quite severe, especially in one not designed to cope.
I'm sure that a good book on helicopter ops (sorry I don't know if they exist because I get my stuff free and complicated from HM) would have all this in.
Yours
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Thanks!
Thanks for the replies...
Good point about the inlet icing. I have heard that people will just keep flying until the wipers start collecting ice. Probably not a good idea. The visibility reference helps, too, to put things in perspective.
I did a little more hunting around and found some interesting weather products from NOAA website(ADDS) regarding icing probability and forecast probability. How does a pilot get online weather info in the UK?
Thanks,
Scott
Good point about the inlet icing. I have heard that people will just keep flying until the wipers start collecting ice. Probably not a good idea. The visibility reference helps, too, to put things in perspective.
I did a little more hunting around and found some interesting weather products from NOAA website(ADDS) regarding icing probability and forecast probability. How does a pilot get online weather info in the UK?
Thanks,
Scott
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Some things about icing in aircraft are not well known. I'll expand that to say that for helicopters, nearly everything about flight in icing is not well know.
Let's start with the clearance is for. Take your mechanical pencil - the one with the 0.5mm lead. Make a dot on a piece of paper. That's the largest size of water droplet that would have been tested for in an icing clearance. Anything else larger is considered freezing precipitation, and there is no aircraft (fixed or rotary wing) that is cleared for, or tested in flight in freezing precipitation. And how do you know when you're in cloud what size of droplets you're encountering?? Exactly - you don't.
Secondly - engine intakes may not have protection against ice ingestion, and nasty things can happen when your engine(s) don't work.
Third - ice can accumulate on the blades and not significantly affect the torque (torque is after all only the drag on the blades). It will significantly affect the ability of the blades to produce lift, and you might be operating much more closely to retreating blades stall and not know it (as the blades produce less lift due to poor airflow over the blades, they get closer to a stall condition at a lower angle of attack - but you knew that.)
So, be very careful about flight in icing - even if you have a clearance for flight in icing.
Let's start with the clearance is for. Take your mechanical pencil - the one with the 0.5mm lead. Make a dot on a piece of paper. That's the largest size of water droplet that would have been tested for in an icing clearance. Anything else larger is considered freezing precipitation, and there is no aircraft (fixed or rotary wing) that is cleared for, or tested in flight in freezing precipitation. And how do you know when you're in cloud what size of droplets you're encountering?? Exactly - you don't.
Secondly - engine intakes may not have protection against ice ingestion, and nasty things can happen when your engine(s) don't work.
Third - ice can accumulate on the blades and not significantly affect the torque (torque is after all only the drag on the blades). It will significantly affect the ability of the blades to produce lift, and you might be operating much more closely to retreating blades stall and not know it (as the blades produce less lift due to poor airflow over the blades, they get closer to a stall condition at a lower angle of attack - but you knew that.)
So, be very careful about flight in icing - even if you have a clearance for flight in icing.
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When I went through my Canadian ATPL licensing conversion earlier this year, there was a great deal of theory on icing, but the bottom line appeared to be, there's no real way to tell when it's going to happen.
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As someone who flies very regularly in icing conditions (especially this time of year), the first thing I will say is that is not entirely predictable. We will assume icing conditions to be present at temps below +1 in visible moisture with vis less the 1k. However engine anti-icing and inlet anti-icing must be on and operational below +5 in order to continue flight IMC as must RIPS. The reason for this is as Lofty touched on, that the reduced pressure of the airflow passing through the inlets will further reduce the temperature of the air, and therefore allow for further cooling of the moisture and possible icing. Ice ingestion into an engine can be a very serious issue and not one to be taken lightly. In sufficient amounts it will likely cause flame out, in lesser amounts certainly compressor stall. Various manufacturers have methods of protection. I remember the lynx and puma also used a physically mounted snow guard on the front as well as inlet anti-icing, to prevent ice shed from other parts of the aircraft, being ingested. The S92 has various systems, including electrical inlet heater mats, bleed air prior to the first stage, and also a particle separator to take out other bits of crap.
Flying in heavy icing and even in aircraft fitted with all the protection available, such as S92, it puts quite a workload on the aircraft. The blades pick up a lot, and the tq increases by up to 20%, and then vibrates as it sheds. This shedding can itself be a problem, as chunks of ice weighing in a several kgs may be thrown from the aircraft. Where do they go? In theory RIPS scheduling should control the build up and allow the shedding in a controlled manner, preventing damaging ice debris from, for example, affecting the tail rotor. This is with RIPS functioning. The airframe collects a lot of extra weight in the form of ice, and this may or may not shed, giving further considerations as to what effect this will have on your aircraft performance. Ice accumulation on the blade has further performance considerations. Depending a little on different blade designs, generally speaking the ice will accumulate from the root of the blade first and then spread out to the tip. Performance issues here with relation to distribution of lift and the modification of the blade profile temporarily have an effect on performance, but importantly will seriously effect your ability to autorotate. Generally the first section of the blade drives in auto and this is also where ice will form first. You can see the scenario developing - a single engine heli in icing, no protection or clearance, develops ice. All fine for a few minutes as the ice builds and sheds in a fairly controlled manner. No problem! Then a large chunk finds its way in to engine, and flame out. Nr decays, lever goes down, Nr decays further." Oh dear" the pilot says, as the icing on the inner portion of the blade prevents autorotational force from driving the blades. Fairly soon the Nr decays beyond a recoverable value, and the helicopter joins the book of statistics.
So in my view, flying in icing is a part of our daily job, but it is in a helicopter tested in icing, where the effects are known and documented. It is fitted with proper ice protection equipment, and if and when this doesn't work we either don't go or vacate immediately. I MOST DEFINITLEY would not experiment in anything without proper clearance. I would also use my own assessment on the weather, not the metman's. If you can see the zero degree isotherm is at 1000' and there is cloud at 1000'. it is fairly safe to assume icing. Of course there may not be, but is it worth the risk? Finally - flying through and getting on top, in an aircraft without clearance - well see the scenario a few lines up. You cannot choose the time for things to go wrong unfortunately, and if you do get on top, you still have to come back through, and several thousand feet of heavy icing without any protection, is not to be recommended. Ice will form in seconds, so 5 mins of descent will be plenty to give you serious problems.
Flying in heavy icing and even in aircraft fitted with all the protection available, such as S92, it puts quite a workload on the aircraft. The blades pick up a lot, and the tq increases by up to 20%, and then vibrates as it sheds. This shedding can itself be a problem, as chunks of ice weighing in a several kgs may be thrown from the aircraft. Where do they go? In theory RIPS scheduling should control the build up and allow the shedding in a controlled manner, preventing damaging ice debris from, for example, affecting the tail rotor. This is with RIPS functioning. The airframe collects a lot of extra weight in the form of ice, and this may or may not shed, giving further considerations as to what effect this will have on your aircraft performance. Ice accumulation on the blade has further performance considerations. Depending a little on different blade designs, generally speaking the ice will accumulate from the root of the blade first and then spread out to the tip. Performance issues here with relation to distribution of lift and the modification of the blade profile temporarily have an effect on performance, but importantly will seriously effect your ability to autorotate. Generally the first section of the blade drives in auto and this is also where ice will form first. You can see the scenario developing - a single engine heli in icing, no protection or clearance, develops ice. All fine for a few minutes as the ice builds and sheds in a fairly controlled manner. No problem! Then a large chunk finds its way in to engine, and flame out. Nr decays, lever goes down, Nr decays further." Oh dear" the pilot says, as the icing on the inner portion of the blade prevents autorotational force from driving the blades. Fairly soon the Nr decays beyond a recoverable value, and the helicopter joins the book of statistics.
So in my view, flying in icing is a part of our daily job, but it is in a helicopter tested in icing, where the effects are known and documented. It is fitted with proper ice protection equipment, and if and when this doesn't work we either don't go or vacate immediately. I MOST DEFINITLEY would not experiment in anything without proper clearance. I would also use my own assessment on the weather, not the metman's. If you can see the zero degree isotherm is at 1000' and there is cloud at 1000'. it is fairly safe to assume icing. Of course there may not be, but is it worth the risk? Finally - flying through and getting on top, in an aircraft without clearance - well see the scenario a few lines up. You cannot choose the time for things to go wrong unfortunately, and if you do get on top, you still have to come back through, and several thousand feet of heavy icing without any protection, is not to be recommended. Ice will form in seconds, so 5 mins of descent will be plenty to give you serious problems.
Shawn (as usual) and Horror Box have summed it up well.
An ice-shed from the main rotor can do a lot of damage...possibly to the tail rotor. Almost as bad is the asymmetric ice-shed. I once had one in a Puma, after popping out VMC on top following a (permitted by the foreign military operator) climb through 3000 ft of forecast light to moderate icing conditions. I have never felt an aircraft shake so much, or seen the Puma instrument panel (soft-mounted) try to exit the cockpit sideways like that. And suddenly it was gone. Thank heavens.
Later, as a test pilot conducting part of some icing trials on another helicopter type, I flew regularly with a boffin who had once nearly abandoned ship after an asymmetic shed during an icing trial in an older aircraft type. He was, so he told the story, sitting in the cabin doorway with his legs over the edge, one hand on the grab-rail and the other to his parachute D-ring, waiting for the Jump command, as said aircraft tried to shake itself to bits. Pilot said 'Jump...Jump...' but never got to the executive third 'Jump' as suddenly the ice was gone and the shaking stopped. A close call for the lucky boffin!
I've said this many times before: don't go where the Flight Manual says don't. Don't trust your common OAT gauge within +/- 2 degrees; if you've got a proper airframe anti-icing fit you'll have a decent gauge (and a Liquid Water Content indicator too) plus some sort of accretion gauges to help you respect the limitations. Do.
An ice-shed from the main rotor can do a lot of damage...possibly to the tail rotor. Almost as bad is the asymmetric ice-shed. I once had one in a Puma, after popping out VMC on top following a (permitted by the foreign military operator) climb through 3000 ft of forecast light to moderate icing conditions. I have never felt an aircraft shake so much, or seen the Puma instrument panel (soft-mounted) try to exit the cockpit sideways like that. And suddenly it was gone. Thank heavens.
Later, as a test pilot conducting part of some icing trials on another helicopter type, I flew regularly with a boffin who had once nearly abandoned ship after an asymmetic shed during an icing trial in an older aircraft type. He was, so he told the story, sitting in the cabin doorway with his legs over the edge, one hand on the grab-rail and the other to his parachute D-ring, waiting for the Jump command, as said aircraft tried to shake itself to bits. Pilot said 'Jump...Jump...' but never got to the executive third 'Jump' as suddenly the ice was gone and the shaking stopped. A close call for the lucky boffin!
I've said this many times before: don't go where the Flight Manual says don't. Don't trust your common OAT gauge within +/- 2 degrees; if you've got a proper airframe anti-icing fit you'll have a decent gauge (and a Liquid Water Content indicator too) plus some sort of accretion gauges to help you respect the limitations. Do.
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I have heard that people will just keep flying until the wipers start collecting ice. Probably not a good idea.
Obviously, there are some days when it's hopeless (and the aircraft should stay in the hangar) but they aren't too common; there is very often a way to avoid airframe icing conditions.
(That should bring on the big freeze for Christmas, watch this space).
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Excellent information!
Thanks guys. This is all great insight and I really appreciate you all taking the time to answer my question! I will definitely stay out of the ice! Fly safely...
Scott
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I would like to add that the ban on flying on top is also for performance reasons - if an engine fails, you must remain in sight of the surface, and be able to carry out a safe forced landing.
Phil
Phil
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What ban? Do you mean in a single?
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Although on that note, while it's not 'banned', flight above the tops of cloud well above the 0Degree even in a twin should be a carefully considered option. Delve into your Operation Data Manual and work out at what height you can maintain Straight and level flight on one engine. You can end in a position where you cannot maintain your clearance from the cloud and end up one engine inop, in IMC, rapidly picking up ice...... sends shivers down your spine... Especially if the onset of ice leads to an inability to maintain above the Safety Alt......
Regards
TGreen
Regards
TGreen
.......And don't assume because you have a clearance to fly in snow above a certain visibility it is always a good idea, or that engine icing and airframe icing are mutually apparent. In a certain rotary (all right a Wessex) which was cleared to operate down to zero (C) with engine anti-icing on from +10 but no airframe anti icing, and in snow with vis/time limits I was unlucky enough to suffer a double engine failure (but luckily not together) whilst well within the supposed clearance - the problem being a build up of fine snow/ice particles in the relatively unheated area of the intake leading to compressor stall. I already had that 'feeling' that all was not well and was diverting anyway (the nearest field was NOT an option!).
Even though I went on to fly Boeing's finest with very good icing clearances (and the Squirrel with none), I still treat any potential snow/ice conditions with a great deal of respect, and the clearances with a large pinch of salt.
Even though I went on to fly Boeing's finest with very good icing clearances (and the Squirrel with none), I still treat any potential snow/ice conditions with a great deal of respect, and the clearances with a large pinch of salt.
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InTgreen,
Good advice, check the ODM, for military pilots, RFM (Rotorcraft Flight Manual) for civvies.
On occasions (obviously, in an IFR equipped twin) I have no option but to fly above cloud. It's not an OEI performance issue for our aircraft at UK operating altitudes (avoiding the airways system above would be more of a problem). Sometimes, if there is an inversion, it is possible to find warmer air above icing cloud and for ice formed in the climb to disperse, but I wouldn't like to bet my life on it. I for one would never climb more than a couple of thousand feet above normal cruise altitude at the very most to try to get above icing cloud (see my previous post).
Having had one bad scare over thirty years ago, at night, in a military fixed wing single, I know how rapidly icing can build up and how severe the effects can be on an airframe and a turbine engine (we got as far as carrying out pre-ejection drills).
Imperative to plan carefully, (in UK the Met Office's F214 is a big help), avoid high ground altogether if necessary, monitor the OAT gauge and stop the climb before you get caught in situation where you might have no option but to enter freezing cloud. Know the en route minimum safe altitude at all times and be prepared to descend to it. If the in flight situation means turning back or diverting elsewhere, do it.
Sometimes the worst ice occurs on the ILS, because of the icing level; then you may have a big problem!
Good advice, check the ODM, for military pilots, RFM (Rotorcraft Flight Manual) for civvies.
On occasions (obviously, in an IFR equipped twin) I have no option but to fly above cloud. It's not an OEI performance issue for our aircraft at UK operating altitudes (avoiding the airways system above would be more of a problem). Sometimes, if there is an inversion, it is possible to find warmer air above icing cloud and for ice formed in the climb to disperse, but I wouldn't like to bet my life on it. I for one would never climb more than a couple of thousand feet above normal cruise altitude at the very most to try to get above icing cloud (see my previous post).
Having had one bad scare over thirty years ago, at night, in a military fixed wing single, I know how rapidly icing can build up and how severe the effects can be on an airframe and a turbine engine (we got as far as carrying out pre-ejection drills).
Imperative to plan carefully, (in UK the Met Office's F214 is a big help), avoid high ground altogether if necessary, monitor the OAT gauge and stop the climb before you get caught in situation where you might have no option but to enter freezing cloud. Know the en route minimum safe altitude at all times and be prepared to descend to it. If the in flight situation means turning back or diverting elsewhere, do it.
Sometimes the worst ice occurs on the ILS, because of the icing level; then you may have a big problem!
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heli iceing
Hello guys
From some time I started to read a lot about helicopter iceing. I also have a little experience with ice on R-44 , just two cases , one during hovering in "backyard" in foggy freezy day just to see how it react - nothing special but ice build up was smaller than I expected in such conditions.
The second case was a bit worse , during cross- country flight through warm front in winter and than ice build up was greater , front windshield was iced completly except two small holes where warm air from cabin heat meet the windshield.I was ready to land immediately if I notice something ubnormal then , but again nothing happend , I didn't notice any change in power requirement , no vibrations etc.It last about 5-8 min and then everything melted , I was lucky that front was really not so wide.
Than I started wondering how it is in turbine helicopters in relations to engine.The most danger is engine inlet I guess.Is it any danger in heli like Agusta 109 where engine inlet is let's say inside fuselage.There is only some kind of net on the fuselage and I guess this is the only danger that this net can be iced and this could cause air flow reduce or block completly but there is no danger that some piece of ice can be sucked from engine inlet to engine like in other helicopters ?
thanks
Happy New Year
From some time I started to read a lot about helicopter iceing. I also have a little experience with ice on R-44 , just two cases , one during hovering in "backyard" in foggy freezy day just to see how it react - nothing special but ice build up was smaller than I expected in such conditions.
The second case was a bit worse , during cross- country flight through warm front in winter and than ice build up was greater , front windshield was iced completly except two small holes where warm air from cabin heat meet the windshield.I was ready to land immediately if I notice something ubnormal then , but again nothing happend , I didn't notice any change in power requirement , no vibrations etc.It last about 5-8 min and then everything melted , I was lucky that front was really not so wide.
Than I started wondering how it is in turbine helicopters in relations to engine.The most danger is engine inlet I guess.Is it any danger in heli like Agusta 109 where engine inlet is let's say inside fuselage.There is only some kind of net on the fuselage and I guess this is the only danger that this net can be iced and this could cause air flow reduce or block completly but there is no danger that some piece of ice can be sucked from engine inlet to engine like in other helicopters ?
thanks
Happy New Year
Icing
Medhawkdriver, there is some sage advice on this subject offered in the posts so far.
Do a Google search using: UH-60 Icing Flight Test Reports and you'll find a couple of pages worth of interesting info. Some good SAE papers in there, but you have to pay for them. Additionally, you might try the AHS. There are, as I recall, a couple of good AHS papers written by Marvin (Lynn ) Hanks, former Commander at the Army Engr Flight Test Activity and also former President of the SETP, on the subject.
Ice forecasting is not an exact science. Most of the manufacturers ( and the US Army ) utilize a fixed wing ice scout machine to go out and find the right conditions, and the inverse of that reality is that someone who sees a forecast of light or trace icing might try it in a non RIPS machine and get an unhealthy surprise.
Good luck.
Do a Google search using: UH-60 Icing Flight Test Reports and you'll find a couple of pages worth of interesting info. Some good SAE papers in there, but you have to pay for them. Additionally, you might try the AHS. There are, as I recall, a couple of good AHS papers written by Marvin (Lynn ) Hanks, former Commander at the Army Engr Flight Test Activity and also former President of the SETP, on the subject.
Ice forecasting is not an exact science. Most of the manufacturers ( and the US Army ) utilize a fixed wing ice scout machine to go out and find the right conditions, and the inverse of that reality is that someone who sees a forecast of light or trace icing might try it in a non RIPS machine and get an unhealthy surprise.
Good luck.