Last night I was flying my LDS 767 in KPHX with the FSX downloaded real weather. The landing runways were the west facing ones. I had a choice of 26 or 25L. I picked 26 for the approach. After I was lined up I disconnected the A/P for a manual landing. About 3 miles from the threshold, I caught a huge updraft, like a thermal, and my altitude went up about 100 feet above the G/S. I tried to nose down to get back on the slope but couldn't get down fast enough and had to go around. On the next try I picked the same RWY and this time let the A/P fly the approach and the same thing occured. The A/P was diving and climbing to keep on the G/S. I decided to go around again and try a different runway, although the landing was possible that time.On the next approach I tried 25L. Manually flew the approach and got the same updraft again about 3 miles from touchdown. I made it this time. I parked and switched to my RealAir SF260 and flew the same two approaches thinking that maybe I had a buggy thing going on in my LDS, but I had the same occurences.The weird thing is, is that I had this happen last weekend flying into the same airport and the same RWY's, and using the downloaded weather.For KPHX I have an aftermarket AFCAD installed from the library here and no other scenery, except FEX, UTX, and GEX. I wouldn't think that and AFCAD could cause this, but I have never had downloaded weather cause an updraft before, and no less on different days at the same airport and on the same approaches.I thought it was wierd, but does FSX model this kind of behavior? I do have turbulence enabled and am not using an aftermarket weather program. I know from having spent a lot of time in Phoenix that since it's so hot there are probably a lot of thermals, but didn't thing that the FSX weather generator modeled updrafts or thermals.I am interested to see if anyone else has noticed this.Thanks in advance.Sean

Yes, FSX weather can model thermals.For example, the sailplane missions obviously use them or else they'd be pretty difficult to do :-)There is also an option on the FSX Weather Settings dialog to enable you to turn on different types of thermal visualization options to better 'see' them.Jeff

Sean,Go fly the Monsoon Approach mission if you want to practice the more likely scenario of a wind shear, rather than an updraft. That mission would probably be a lot of fun in the Level D 767.Cheers,

There are a few airports where FSX puts the thermals right in the glide slope. KSNA has one about a mile or so before 19R, but I think that one causes a downdraft. It's irritating to have the same thermal in the same path every single time. They should have made them randomly generate at each start.

>It's irritating to have the same thermal in the same path>every single time. They should have made them randomly>generate at each start. The reason that you find thermals in roughly the same area is because aside from mission specific ones, each type of FSX landclass has an associated description for its thermal properties.So just like in the real world where certain types of land coverage such as rock, roads, vegetation, marsh, etc., provided different types and levels of thermal behaviour, so it does in FSX. As the type of land does not change randomly when you start FSX, neither do locations of the associated thermal properties. They do however change in properties such as the radius of the thermal between defined max and min values, the height of the thermal, the rate of lift or sink in the core, turbulence level, etc..Jeff

Thanks for the replies guys. I never knew that they were modeled like that. I had never noticed before when flying into KPHX. Are they triggered by temp. For example they only show up in Phoenix when the temp is above 90 degrees or somthing to that efect. I have only had FSX since April and since I usually fly with real weather I had never noticed the thermal effects before in that area, but maybe it was because the real weather was not hot enought?Thanks again. I am glad to know that I don't have a bug there.Sean

I am pretty sure thermals are triggered by season: summer-type weather has the most pronounced thermals, and the other seasons not so much. I don't think that actual temperature is involved as much as the landclass state during the season. If you can edit your landclass, you can edit the thermals indirectly, or I think you can edit them directly with the SP2 SDK. Jeff ShylukAssistant Managing EditorSenior Staff ReviewerAVSIM

Thanks Jeff. It's funny, I just flew into KPHX last night with RW weather and this time got the east facing rwy's. I used 7L and it had no thermal effect. I guess it must be the land class, cause I get the thermal effect on the west facing runways, and the temp was about the same last night as it was the other day when I got this effect. I am using Scenery Tech landclass. I never knew until this, that landclass had thermal properties built into it. Just thought they were for placing cities, farms, forests, etc. Learn something new every day.Sean

By default FSX loads turbulence and thermals on approach at many airports in the database. If you do not want them then go to settings|display|weather and place a checkmark in the box that disables turbulence and thermals.

I wish I could disable the thermals, but keep the turbulence, without having to buy an aftermarket weather program. I am actually pleased for the most part with the default weather that FSX came with, now that I can run it full out. The theramls are not that big a deal, just never noticed them before when on approach in a heavy.

You can turn off autogen thermals by renaming ThermalDescriptions.xml,such as changing xml to orig. You could also go in and edit it. Here are some comment lines in that file, to give an idea: As an alternative, you can turn off the default thermals, download and use CumulusX! instead, which injects thermals and allows more tweaking (requires sp2).scott s..