Airbus descent problems

  • After not flying the plane for a long time I am flying the Airbus again. I noticed that I get into problems everytime during descent. At a certain time the plane switches to SPEED mode and then the green dot on the altitude tape drops down quickly meaning the plane can't keep the vertical path anymore. Of course I use the speed brake as soon as I see that happening but there is no way the speed brake can help here. Due to this I end up a few thousand feet (!) too high on approach. This has happened during all my (3) flights so far.


    Anyone else having this? Is there something wrong with the AP logic somewhere? The next time I will simply start my descent early on (for instance as soon as the TOD comes into view on the display) but well, the plane obviously should be able to get to the correct altitude when you start the descent at the TOD...

  • I redid my last flight and this time I started descent as soon as the green dot (on the alt tape) started to move down and I used the speed brake to stay underneath that dot. Whenever SPEED mode was engaged, specially above 10.000 ft I immediately engaged the speed brake no matter what the green dot did. This time I managed to approach the airport while flying underneath the GS indicator. The problems mainly arise while still above 10.000 ft. After reaching 10.000 ft and still being at the green dot I didn't really get into problems anymore.


    What does the Aerofly 'flight management computer' give you?

    A far lower fpm for sure. Specially when SPEED kicks in above 10.000 ft.


    It's nice knowing how to handle this (while still using managed mode) but I wonder if a real life Airbus pilot would use the speed brake this much...?

  • I always wonder what exactly the green dot means. Is it strictly your position relative to the path or does it combine position and speed changes. A real VNAV path should calculate the exact path, including future speed changes. Since my system seems to keep the aircraft below the indicated path, that might be for the speed reduction. Since the normal top of descent is manual, I do start down shortly prior to the path change.


    But I have problems on both the 737 and A320. In both cases, strange things happen around the 250 Kts slowdown approaching 10,000 ft. The 737 will never recover and lose the path completely and the A320 will add power, put itself above the path and then request drag to slowdown even though the power does not seem to be at idle. Maybe the airplane is not designed to use idle thrust due to some requirement, I do not know.

  • The vertical deviation in the 747, A320 and 737 all work the same in Aerofly. The vertical deviation uses a rule of thumb to calculate the top of descent which also factors in future speed reductions such as the 10000ft reduction to either 250 or 240kts as well as the speed reduction from that speed down to the approach speed. Currently it doesn't factor in any head or tailwind component, this might be the issue you are currently experiencing.


    When the A320 autothrust goes into "SPEED" mode it means that you are flying too slow. Usually it should remain in IDLE for a very long time until you hit the level off segment at which point you're already capturing the localizer. If you feel that you are not descending fast enough you can always pull out the altitude knob and force an IDLE descent, speedbrakes can be extended to get down quicker. You could also extend speedbrakes and push the expedite button but this disregards all speed constraints.


    There are probably 1000 changes in the autopilot along that have been accumulating over quite some time and those will be released with the next updates. So changes are that this issue will resolve itself then. I've never had any issues with the vertical deviation being off that much, we'll test that before the release of the next update of course.

  • When the A320 autothrust goes into "SPEED" mode it means that you are flying too slow. Usually it should remain in IDLE for a very long time until you hit the level off segment at which point you're already capturing the localizer.

    I only fly in managed mode so if I am going to slow it must be the system not performing well...?



    There are probably 1000 changes in the autopilot along that have been accumulating over quite some time and those will be released with the next updates.

    Good news!