>I froze my nuts off once. That was pretty scary.Well how did you get them back on?:-erks

Structural and Pitot icing is modelled.For structural icing simply try this:Load up the Cessna with something like -2 or -3 deg cel and heavy rain. Start your takeoff run and time how long it takes to loose control! It won't be too long.However, the pitot icing is naf naf naf in FS. It simply zeros the ASI (even though the Mach meter still functions...LOL!). In reality it is quite likely that the ASI would stick at the speed you were doing when it iced over. You can imagine how insidiously lethal this is in RL - the real airspeed is falling because of ice, but you don't notice because your ASI says everything is fine. An example where cross checks are vital, in this case does MAP match the airspeed, if not then something is wrong.

Your statement about how the airspeed indicator acts when a pitot tube is blocked is not correct. The pitot tube has two holes: the ram air hole and a drain hole. If the hole for ram air freezes over and the drain hole remains clear, then the airspeed indicator drops to zero. If both the ram air and the drain hole freeze (and the static port remains clear) then the airspeed indicator remains fixed, except in the case where the aircraft climbs or descends. In this case, when the airplane climbs, the airspeed indicator shows an increase; if the airplane descends, the airpseed indicator shows a slowing. When the static port is blocked and the pitot is clear, then the airspeed indicator responds normally to changes in velocity if altitude remains constant. When the aircraft descends at a constant velocity the increase in density of the air results in a higher dynamic pressure and the airspeed indicates an increase in airspeed. When the aircraft climbs at a constant velocity the reduction in air density with altitude means a reduction in dynamic pressure against the pitot tube and the airspeed indicator shows a decrease in airspeed. One expects a decreased airspeed during climbs and an increased airspeed during descents; however, the airspeed indicator will not be accurate.

Of course my explanation is correct. If the pitot freezes, it is quite likely that the drain hole will freeze. As the frozen needle scenario is the most insidious, then it is the one that should be modelled. The silly tell tale ASI dropping to zero is too simplistic.

I disagree. The drain hole is not as likely to freeze as the ram air port on the pitot tube. Ice forms preferentially on sharp protrusions and leading edges on the airframe (See figure 97 "Aviation Weather" FAA Advisory Circular AC 00-06 www.faa.gov which is a very nice illustration showing how a pitot tube freezes up - the ram air hole is completely covered and the drain hole is completely clear) so its more likely that the ram air port would get blocked or obstructed before the drain hole. I also don't agree that the 'frozen needle' scenario is any more or less insidious or difficult to identify than when the airspeed indictor drops off because the ram air hole is blocked - with a regular scan including cross check and interpretation, and an awareness of power pitch and performance characteristics of the aircraft, it is certainly possible and expected that a pilot would be able to correctly identify that the airspeed indicator has failed and the cause of the failure - whether it is due to a blocked static port, blocked ram air port, drain hole, or combination.I do think that the modeling for the airspeed indicator failure modes is correct in the flight sim. I've seen it both ways in the flight sim - where the AS drops off, and where the AS does not respond as expected to changes in the performance of the aircraft. Either way it's a challenge and can be unnerving as you say to fly without a function airspeed indicator!

You have to remember that the wings are usually the last place for ice to form. We've always been told to look for ice on the OAT probe sticking out the windscreen, it's the first place to visibly accumulate, followed shortly by the prop hub (which unless you're in a multi-engine, you probably won't see).I've always wondered, could thee be sort of an animated gauge for icing, like on Piper aircraft, have a guage that "builds" ice in to OAT probe and/or wings. It would just be a sort of texture. Just a thought.----------------------------------------------------------------John MorganReal World: KGEG, UND Aerospace Spokane Satillite, Private ASEL 141.2 hrs, 314 landings, 46 inst. apprs.Virtual: MSFS 2004"There is a feeling about an airport that no other piece of ground can have. No matter what the name of the country on whose land it lies, an airport is a place you can see and touch that leads to a reality that can only be thought and felt." - The Bridge Across Forever: A Love Story by Richard Bach

>I also don't agree that the 'frozen needle' scenario is any>more or less insidious or difficult to identify than when the>airspeed indictor drops off because the ram air hole is>blocked - with a regular scan including cross check and>interpretation, and an awareness of power pitch and>performance characteristics of the aircraft, it is certainly>possible and expected that a pilot would be able to correctly>identify that the airspeed indicator has failed and the cause>of the failure - whether it is due to a blocked static port,>blocked ram air port, drain hole, or combination.>Also, these day's, with the availability of GPS for almost anyone; it's easy to notice a sudden large variation in what the airspeed indicator (IAS) is saying versus the groundspeed readout from the GPS. Since it's always a mental exercise to be figureing winds, true airspeed, etc. while flying along on auto-pilot :), I'd just probably notice the airspeed indicator just crapped out soooner than later. L.Adamson ---- I have a heated pitot setup in the garage, and was ready to blow frozen water particles at it. But now I won't have too! :D

Thanks for the link. I could only locate an Airport circular with the number 00-06 and it appears to be cancelled. However, I did find AC 91-43 that supports my view. This is exactly the situation that the UK CAA are so hot in the ATPL exams. Rightly so! The spate of ice related biz jet accidents in the US last winter spell out just how insidious icing problems are (whatever the specific issue).I am suprised to read that you think a zero ASI is no less obvious that a frozen needle!? The ASI is part of the primary scan, the MP is not. An educated pilot will notice the MP not matching the ASI pretty soon. But you don't get educated pilots without the issue being raised and hopefully tested in the sim. An uneducated pilot will just get more confused until the stall...which is silent because the vane is frozen too.I think we had just better agree to disagree ;)

Again I disgree (becoming a habit this!) I don't think anybody would be immediately alarmed at a change in GPS ground speed. GPS is prone to clock error and the UHF signals are very weak and prone to inadvertant jamming. Even a RAIM system may take a few seconds to identify a duff satelite and bin it.However, a air test pilot I know recently suffered from a lessening airspeed after take-off when trying an aircraft out after its annual. He just flew by power settings to an uneventfull landing. Somebody on the ground did mention GPS ground speed, he did say "I didn't think of that!".

>Again I disgree (becoming a habit this!) I don't think>anybody would be immediately alarmed at a change in GPS ground>speed. GPS is prone to clock error and the UHF signals are>very weak and prone to inadvertant jamming. Even a RAIM system>may take a few seconds to identify a duff satelite and bin>it.>My watch is set to the exact GPS "atomic clock" second. I own four GPS's and they'll all agree to the second. You'll even hear the "bell" for national radio news cast's at the same second.In 25+ hours of cross-country flight last November, the GPS never failed once that I was aware of, except when I put a bunch on maps on top of the glare-shield mounted antenna (plane has clear canopy).My truck's GPS and XM satellite radio have never went off line except in a few canyons and under overpasses during the 1 1/2 years I've owned it. With 22 GPS satellites orbiting the earth, my GPS is capable of picking up 12, and usually always has nine on line. GPS failure these days is very remote. In fact, some new high tech auto-pilots use GPS information instead of spinning gyro's. My auto-pilot which is one of these, has a solid-state gyro which fit's in a 1/4" cube.A year ago, I took a poll from a number of pilots using GPS, regarding GPS failure, and it's almost a non-event . Big time GPS failure is a popular myth these days, that's usually spread by those that don't use one. I've been using moving map aviation GPS's since the early 90's, and they've come a long way!L.Adamson

Well this has been an interesting chat and I've thouroughly enjoyed and respect your viewpoint. Surprised that the FAA link to the advisory circular is not accessible - I know it's there I just got downloaded a copy about 2 months ago - i'll post a link when I get a chance. Thanks for your time and interest and best regards.

I would be interested if you can provide a link. We were given a schematic during my studies, but the FAA doesn't always agree with the CAA on some issues. It is good to get another view.Cheers!

Satellite clock error is rare but not unheard of. The most accurate 2D fixes are three satellites 120deg apart. A forth satellite is needed to provide geodetic altitude. If a satellite

>Structural and Pitot icing is modelled.>>For structural icing simply try this:>>Load up the Cessna with something like -2 or -3 deg cel and>heavy rain. Start your takeoff run and time how long it takes>to loose control! It won't be too long.>Ok , but does any weather program such as ActiveSky is able to simulate structual icing as well ? Ericson

>Ok , but does any weather program such as ActiveSky is able to>simulate structual icing as well ? Wrong question. Icing can't be "simulated" by a weather program, icing can only be simulated by the "aircraft" simulator. So it has nothing to do with ActiveSky.Michael J.WinXP-Home SP2,AMD64 3500+,Abit AV8,Radeon X800Pro,36GB Raptor,1GB PC3200,Audigy 2http://www.precisionmanuals.com/images/forum/747400.jpg