Hello everyone,
I noticed since a while ago that sometimes when we are starting the descent and that there is an altitude constraint, the FMGC will go to the descent phase and all of the sudden the progress page will display a erroneous VDEV of eg +3000 feet but before we engaged the descent, the TOD arrow was still way ahead of us. And therefore the aircraft will go thrust idle and then again in speed mode when VDEV = 0 and the next TOD arrow ( accurate this time) will be well ahead of the point where the aircraft will capture the « profile » calculated by the FMGC. I would like to emphasize there was no geometric segment, I reinserted the CI during descent to see if it will update the predictions but it stayed the same. Manage speed was used. It was the first altitude constraint manually inserted during cockpit preparation on ground. I took pictures tonight to show you.
You can see in the first picture the alt constraint at GYA of FL187. The aircraft is in managed descent in thrust idle but in reality we should be below the profile but as you can see especially in the second picture the FMGC thinks we are 1000+ feet high ( it was +3000 when we start the descent) and then it went back to speed mode until it reached another idle segment... Any idea why those weird predictions happened?
I also noticed sometimes when it entered the descent phase, the VDEV will show something like we are too high but will keep speed mode with a vertical speed of 1000 feet/min. This often happened on waypoint NOLON for those who fly in China with an altitude constrain of FL177 which is also the first altitude constraint.
Thank you for your comments.
https://ibb.co/e8oU5H
https://ibb.co/iMp2QH