found strange problem in 737NG, take off when cold temps...

[clayton4115 56]

hi allive recently decided to fly in Europe lately as ive never dont much Europe flying in the past and i only fly the PMDG 737NG 800 series,however lately ive been having a problem with the VNAV on this aircraft when departing very cold icy airports like places where temps are 5c and belowthe problem is once airborne and i engage VNAV and at approx 4000' i lose all speed on the 737 and the tape speed goes to RED and indicates 45 knts, then i did CTL Z to see what the speed is and it states im doing 0!once this happens my plane doesnt climb anymore and no matter what i do i cant climb,so i decided to do a summer weather and it took off ok with no problems with VNAV or anything else, so my guess is it has to do with very cold airports as ive never experienced this before,does anyone else have this problem, if so how can i fix this?p.s im using V3.50 of FSUIPC.dll the freeware version,rgds

[dave_paige 11]

My initial guess would be that your're forgetting to turn on your probe heat on the overhead panel after starting the engines. With the pitot tubes blocked with ice you'll no longer get any indicated air speed.

[clayton4115 56]

hiwhere is the pitot heat switch in this overhead panel?http://forums.avsim.net/user_files/135279.jpg

[Guest Robin.B]

Probe heats are located just under the Window Heat switches towards the top/right.

[ronzie 21]

If flying through moisture laden clouds it might be wise to engage engine anti-ice as well. This seems to be standard procedure for high altitude flying once past the take-off stage where a bit of power can be shaved to run it.Any heavy moisture also requires wing deicing as well. usually applied when OAT - TAT is 10 degrees above freezing or below.Sincer FS9 does not emulate deicing ground stations I also suggest you taxi in moisture near or below freezing with wing deicing on (don't forget to have engine bleeds on), turn it off for the initial take-off climb over obstacles, and then turn it back on when you can afford a bity of power loss. Built up structural ice drag can have a major impact on take-off and climb performance as well as changing the shape of the leading edge of the wing that can induce stalls via airflow distruption.Just a loosely related issue that pertains to cold weather operations.

[Guest whartonp]

I also have had this problem for quite some time now and i can confirm that it has nothing to do with the pitot heat being off. Also wing and eng anti ice should not affect the air speed indications.I think that this is a problem that needs addressing by PMDG. I have the latest FSUIPC and am fully up to date with all updates.So PMDG can you investigate this in some way pleaseMany thanksPaul Wharton

[ronzie 21]

You are correct in that structural and engine de-ice do not directly affect airspeeds except for the small engine power loss due to the bleed air off the later stages of the turbine if used for these.I was just mentioning these as additional anti-ice precautions.The parasitic drag of structural ice however does affect airspeed in the sense of changing the lift/drag vectors and change of wing shape leading to slow loss of airspeed due to compensentory pitch up change, not the sudden effect of probe problems.

[Guest tmetzinger]

I think this is an FS9 problem, as I have similar things happen (airspeed goes to 0) in cold wx in clouds in the B1900, and other non-PMDG airplanes. FS9 seems to want to simulate the melting process as opposed to never letting a hot pitot ice up.Selecting VS mode can allow you to climb.

[Guest upside]

BumpPMDG you really do need to respond to this. It is not acceptable to just ignore a problem like this even if you do not have a clue what the solution is.:-mad

[Guest tmetzinger]

>Bump>>PMDG you really do need to respond to this. It is not>acceptable to just ignore a problem like this even if you do>not have a clue what the solution is.>:-mad And YOU, sir, need to sign your name as the forum rules require. I'm pretty sure this topic has come up before, and perhaps a search of the archives might shed some light.For folks with this problem - a good workaround if you're climbing in VNAV is to immediately select VS mode when the airspeed drops off. That will maintain the current VS, the autothrottle should be in N1 mode, and you'll have a good climb profile until the ice melts.If you're in LVL CHG, be sure to switch to VS/N1, and NOT VS/SPD.Best wishes,

[Guest upside]

I dont want a work around i want PMDG to ackonowledge this problem and preferably undertake to resolve the issue.I dont think that that is to much to ask. On the other hand maybe PMDG are not interested, its starting to look that way isn't it.Paul Wharton

[mnmon 0]

I can confirm that this is *NOT* a PMDG problem! I have this effect in EVERY aircraft at various times. I always fly with ASV loaded with the latest weather and always make sure the pitots are heated. The problem shows up when through clouds, or near certain thunderstorms, I get the airpeed indcator going to zero until I pass through the conditions. I haven't figured out what FS9 is doing in terms of circumstances that trigger this. But, it just happened yesterday with the Flight1 MD80. I have an unregistered FSUIPC so I don't know if it has a fix, but I've just assumed it's a bug within FS9, and have lived with it. Mike

[Guest tmetzinger]

I did testing this morning - same results. Fly through airspace where ASV gives you icing, and you get an iced over pitot for a few seconds and no airspeed. Doesn't matter WHAT aircraft you're using.So this isn't a PMDG problem. I got the same effect in the Lear, the B1900, the Mooney, and the DC3.

[JRBarrett 3,034]

>I dont want a work around i want PMDG to ackonowledge this>problem and preferably undertake to resolve the issue.>I dont think that that is to much to ask. On the other hand>maybe PMDG are not interested, its starting to look that way>isn't it.>>>>Paul WhartonThe problem of zero indicated airspeed in cold temperatures is a well-known FS9 bug. It has absolutely nothing whatsoever to do with PMDG aircraft. The same thing will happen with ANY FS2004 aircraft - default or add-on.Evidently FS9's internal logic relating to ice build-up in the pitot tube is too "aggressive". Ice will form, even if the pitot / probe heat is turned on well in advance of takeoff... especially when flying in or near clouds - even for a short period of time.There is a solution, but it requires the registered version of FSUIPC, which gives you the option to completely disable airframe / pitot tube icing. This particular problem is a Microsoft error, and is not the responsibility of any aftermarket panel or aircraft developer.Jim Barrett

[AlaskanFlyboy 7]

Fortunately, it only seems to do it once, and not continually ice then thaw, then ice again later on a cycle.----------------------------------------------------------------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