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Guest Agrajag

How many altimeter changes are normal?

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In my flights I've getting altimeter corrections SEVERAL times per flight for 40 minute flights and they're often quite far ranging. One moment I'll get 2989 and within 10 minutes I'll get another update for 3010. Then 10 minutes later, 2994 and so forth. I'm just curious if this is proper operation or if I've got something else goofed up somewhere or if MS' ATC with a rare change (and usually only as a result of LONG distance or altitude) is more realistic.I also had one other altimeter oddity. I used the co-pilot for the first time which showed me some interesting interaction and gave me correct procedure and such but one thing was interesting. ATC came back with "Altimeter 2989 but the co-pilot wouldn't move the altimeter from 2990." That's what got me to thinking that perhaps all these errant altimeter changes were incorrect.

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Here's the data from my last flight, a 1 hour flight from Dulles (KIAD) to Philly (KPHL) shown is the altimeter reading and whether I was ©limbing, (L)evel or (D)escending:3119 On ground3008 C2995 C3010 L3015 L3026 L3024 L3015 L3008 L3015 L3021 DThat was all of them from start to finish.

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what weather program are you using, and what is the fsuipc pressure smoothing setting?jd

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Using the default MS "real weather" that it downloads every 15 minutes. However the updates, as you can see, are much more frequent than that.I own FSUIPC and have never touched that setting so it's likely default. Hold on, heading in to check it. Okay, "Smooth pressure changes" is NOT checked.I take it from your post that this does seem very excessive to you. I also notice that hitting B almost never matches what ATC is saying it is. It's usually close but not matching.

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i don't have any control over the weather. if ms weather changes the pressure on you, all i can do is report on it. better than not reporting it, and you being too high or too lowby the time you hit B, the pressure has probably changed some more.jd

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I agree JD but wow, is that really what pilots experience or is MS totally hosed?

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i don't think that is what pilots experience. i can't imagine drastic pressure changes within a few miles. but heh, i don't control the weather, i only report it :-)jd

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I THINK FS rolls up to the actual settings. For example, I came in tonight for a flight from Philly to Newark (short) and it started out at 3014 on the ground and nearly as fast as I could hit "B", it changed while still on the ground. 3016, 3017, 3020, etc., all the way up to 3038 where it leveled and then wouldn't change until I got airborne.

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Pete Dowson may have hit the magic element. He first commented that MS weather "settles in" which explains the beginning numbers I saw. He also said it appeared to him as if these represent crossing different weather towers which are often read at different times so they often don't match. If so, that's a major issue and one that should prompt some sort of solution either in the form of pressure smoothing (more averaging really) or for RC to allow for not passing on this so often. It's my view that no flight should be made up primarily of altimeter change commentary.

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activesky and fsmeteo do exactly that, they smooth the pressure changes. that is what the fsuipc setting is for, also. but the fsuipc setting does not work with ms weather.i update the pressure every 10 miles, which seems reasonable. i also update you on the pressure, if the amount of pressure change has caused an altitude deviation.jd

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Thanks JD. Seems I have a choice to make then. I really don't see the need for yet another add-on product (Active Sky for example) and really like MS weather but if it's going to cause me to be interrupted every 3 minutes for an alimeter change, that's going to be annoying.I have found one by-product of this to be an issue. One change was drastic enough that it cost me a clean flight. I last was given 2998 and was flying that. Next thing I know I've being told to watch my altitude so I hit "B" and it jumps to 3044. No sooner had I hit "B" when ATC comes on and gives me 3045.How can I be held responsible for flying out of deviation settings when I had no way of knowing (short of cheating) what the current settings are? In this case I would argue that RC needs some logic to be aware that I am flying the correct altitude based on the last given setting.

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