ISSUE DESCRIPTION
During initial climb in A321LR with autopilot, the aircraft goes maximum pitch angle without any consideration about vertical speed or airspeed limits. Happened without either having reached overspeed limit or being late in the vertical nav path. Airspeed decreases rapidly until it reaches A.FLOOR protection and autopilot disconnects. If reconnected immediately, the autopilot behaves exactly the same.
(Nb : I have checked this other issue but it doesn’t seem to be related as my issue is that AP is commanding seemingly an infinite positive vertical speed with autothrust being nominal in CLB setting while this other issue is that the AP disconnects and autothrust goes TOGA)
Post-Scriptum : after capturing this video and publishing this bug report, I noticed that the AP was in altitude capture mode, which is invalid as I was 20’000 ft below instructed altitude (15’000 vs 35’000), which can explain the AP’s behavior. I do not know if that was the case the first time I encountered this issue (prior to the video capture), I will pay particular attention if I encounter this issue again (if this is indeed the cause of the issue that would be a “AP switches to altitude capture mode far too soon during climb”)
FREQUENCY OF ISSUE
Encountered just once in my 3rd flight with the A321LR. Will update if I encounter it again.
REPRODUCTION STEPS
Unclear… below is the situation I was in when I encountered this issue, will update if I manage to identify what is triggering it:
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Fly the A321LR (career passenger mission)
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Connect autopilot right after takeoff during initial climb (flying an RNAV SID with altitude constraints (unsure if related, aircraft was well above the minimum altitude constraints))
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… ?
Workaround
- Disconnect AP (if not already reached A.FLOOR protection) and reduce vertical speed
- if A.FLOOR protection has already been reached, disconnect autothrust after reducing vertical speed and let airspeed increase to a safe value
- Manually set a reasonable vertical speed / flight path angle and reconnect AP (+ autothrust if disconnected)
- alternatively, you can set a manual airspeed instead of a manual vertical speed, that will also prevent the aircraft from climbing too fast
- Later on the flight, try reverting to fully managed airspeed / vertical speed (issue may happen again if reverting too soon)
YOUR SETTINGS
[PC Only] Are you using Developer Mode or have you made any changes to it?
No.
MEDIA
What you can see in this video :
- 0:00 - AP is disconnected (the issue occurred already once) ; RNAV SID constraint is that I should be above 7000ft, I am currently above 14’000 ft so no pb
- 0:10 - after waiting sufficiently so that airspeed is within safe range, I reconnect AP → AP increases airspeed indefinitely even if airspeed is falling down in the amber unsafe zone and vertical speed is going in the positive amber unsafe zone
- 0:37 - was about to reach A.FLOOR so I disconnected AP and manually lowered the nose