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Airbus does not abide to the set vertical speed

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Sometimes A319 refuses to descend. Let's say, I'm at 12,000 ; ATC says "descend to 7,000". I pull the altitude knob on MCU so it's in selective guidance mode; I also set the vertical speed. However, Airbus does not abide. After several seconds, the numbers of the versical speed are replaced with dashes; if clicked again, the number is different from what I entered.The attached screenshot shows the opposite situation: even though I set the vertical speed at -200, Airbus is descending with much higher vertical speed. It would be nice to know how Airbus decides what vertical speed to maintain. This non-abiding often results in quite nervious situations when flying online with live ATC.thanks,Vadim Rapphttp://forums.avsim.net/user_files/141789.jpg

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Hi VadimI read your post as as you have had no answers from the experts I thought I wouild try an answer. You say in your post that you PULL the altitude knob on the MCU. In my opinion that would put the plane in OP descent (or climb) mode which is clear from your pfd shown seecond column from the left. This means that the plane is going to descend acording to some other logic, but not vertical speed logic selection. In my opinion when you pull the vertical speed knob you should leave the altitude selector alone so that the plane commands the vertical speed mode in the pfd according to the -200 you set in the window. I will try this in a test flight to see if my answer actualy holds water, and if it doesn't then i will come back and post an amendment.best regardsJohn CallejaBAW 352ps. I tried this before posting. to descend from a known altitude using an OP descent you just dial a number in the altitude window and Pull the alt knob and the logic sorts it out. But as you want to make a descent using vertical speed , then from a known altitude (so it has ALT or alt crz in the pfd) you first dial in your required altitude in the window then just pull the Vertical speed knob and dial in your descent rate and leave the altitude knob alone and it will put vs-and your dialled vert. speed selected in the pfd. and make the descent

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Simple way to remember.Pull = I have controlPush = You (the airbus) has control

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Hi NormanThanks for making the simple rule in your reply, but I feel it is too simple, and the original poster has got into unfamiliar territory because he applied the simple rules to the wrong control. I agree with what you say about pulling and pushing as regards to the Vertical speed control, but not the Altitude select control, as pushing or pulling still leaves the airbus logic in conrol but in two different modes of control ie controlled descent (or climb) and Open descent (or climb) I dont think the pilot has any control in either of these modes, as the original poster found out in error.regardsJohn Calleja

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While Airbus usually abides to the settings at relatively high altitudes, it's not the case during the approach. I'm sure if you try to reproduce the same situation as in my picture, you wil see it in 2 minutes. Pull the altitude knob, push it - it does not matter: your setting of the vertical speed is simply ignored. I'll now try to make a video.

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I have uploaded zipped 1MB divx video file to www.vadimrapp.com/fs.zip . Watch how changing vertical speed has no effect on the descend. If the altitude knob was in managed mode, i.e. with the dot, it would be the same. Airbus simply ignores any setting of the vertical speed. In this case it is descending, but in other cases it does not want to descend, despite managed or unmanaged altitude and any vertical speed. It looks like it takes into account not what's set by the altitude knob, but rather the calculated altitudes at various points of the approach; so if it thinks it's too early to descend (i.e. the purple dot in ND is high), it won't, even if I set the altitude knob

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Hi againI watched your video and decided to take the bus up and try a few things. I reached cruize altitude of fl290, and then decided to descend to f220 using an op descend which it did instantly, and during the descent intervened with a vertical speed descent of 500 ft/sec and it obeyed this directly, so all well so far, so took it back to fl290. as i am flying as i am typing this i need to do similar as we get nearer and nearer the airport, so will be editing this post as we go regardsJohn Calleja

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Hi againSorry this has to be a reply as i was not aware that there is a time limit on when you can edit a post. My next task was to repeat the above at a few miles before the top of descent. I set the alt knob to fl 250 and pushed the alt knob for a managed descent, but although it showed des in the pfd the plane barely descended by say 50 ft in 2 minutes, so i tried a op descent and when i pulled the knob i got a crash to desktop, so had to abort the flight. will try again maybe tonight or tomorrow, time pending, but at this rate i recon we will both need some help from pss, but i will persevere as i feel i am on a mission now.regardsJohn Calleja

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With managed, it's expected - that's when airbus decides what to do by itself, according to the position of the purple dot on ND. It's what crashed to desktop on you is what we will try to show. I'll try to reproduce it.While you are at it, could you also watch for another situation that I described here: http://forums.avsim.net/dcboard.php?az=sho..._id=6295&page=4 . Yesterday I had it again when trying, but as usually, only once, and then couldn't reproduce.

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Here's another video, somewhat related - shows how Bus does not abide to the heading as well. After that, switching the heading back to managed is not easy - you click on the knob, but the dot does not appear at once - this can be seen in the video, when a click on the knob already in "manual" mode does not result in the dot appearing next to it; so for some time you are stuck in the "manual" heading that is not followed, and can't even switch back to the managed one.I have uploaded the plan. When airborne, I specify arrival runway ILS31C at KMDW.Vadim Rapp

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...here you go, here's the video of non-abiding to the descend, same flight. The trick is in not following the approach plan in ND, a usual situation when flying online with live ATC; in this case, it would be the most usual "fly heading XX, descend to YY". To abide, I switch heading to the manual mode, and then when I change the altitude in order to descend, there's no effect. I think the video well illustrates pilot's panick :)The solution, it appears, is to click once again on the vertical speed knob, so it changes from the already set -2000 (or whatever was set) to zero; and then turn it to the same negative vertical speed once again. That's when Airbus will listen and will start the descend - on the second request.I'm not sure I understand the logic behind all this. Would be nice if PSS explained.Vadim Rapp

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HI VadimI have now copmpleted a satisfactory landing using just op descend and intervening with v/s possibly 10 times during the descent and all was well. I have kept a log of everything i did, it may be a long post but i will try and type it. I also have a screenshot but no video. Also i noticed in the video that you pressed the switches but didnt wait for the speed to bleed off, the plane wont descend in op descent until the speed has bled off to the magenta mark ( I think) so here is my long post,Climbed to top of climb fl290. Soon after made several des. to fl 250 using op des. and intervened with v/s many times then back to fl 290 with controlled climb. Repeated again at a few miles from Top of descent. stayed at fl 290 till Top of descent. desc. from tod to 7000ft using op des and intervened with v/s a few times. Descended to 5000 ft as above with both op and v/s. Descended to 2900 ft using both again. (runway is 1487 above sea level) so held 2900 till final turn and just used v/s to drop it on the runway all ok. I will post my screen shot seperately as i am not sure how to do it.Ah can see now how to attach. so it seems the plane behaved itself, so u must have a individual problem with set up or files which i can't help with but for me the plane is sound. If i was re installing from scratch. i would have to ask advise about what to re install ...like fsuipc...and the ini file...the cfg file as well as the planes but that stuff i leave to the gurus. i just wanted to do a flight to share with you if it worked or not. and in my case it did.regards John Calleja

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Hiya had to send the screenshot seperate cos it was telling me i had exceeded the limit so had to zip it up

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Also i noticed in the video that you pressed the switches but didnt wait for the speed to bleed off, the plane wont descend in op descent until the speed has bled off to the magenta markNo, that was not the case. Here's another video that shows it.I think I understand now: note how in the video airbus did not descend when the mode in ND was "Alt", and started descending after the mode became "VS -1000". This means that in order to start descend in open mode, we need to1. set the desired altitude with altitude knob2. click on the vertical speed know, which puts "VS" mode on ND3. turn VS know to the desired vertical speed.If (3) goes before (2), ND remains in Alt mode, and Airbus does not descend. I don't think it's right, because doesn't "Alt mode" mean that the specified altitude would be somehow maintained. But at least I see now how to start the descend.Vadim Rapp

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Hi again Vadimseems that you have found a way of working the bus to how you want it to operate. ihave unzipped your flight plan and put it in the correct folder and will fly it Saturday. If you want me to do any more testing with you just ask, but think you have a solution for now which will work.regardsJohn Calleja

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