The A320 FCOM chapter 27 flight controls, normal law, protections, shows a diagram how the sidestick input is used when protections are active. When high angle of attack protection is active the side stick controls angle of attack (alpha protection to alpha max), so far so good.

In several places throughout the FCOM and that diagram I talked about Airbus states that the alpha protection has the highest priority.

Does this mean when alpha protection is active that pitch protection is no longer available? It makes sense that the nose of the aircraft is allowed to drop below the normally protected minimum of 15 degrees but is the maximum pitch of 30 degrees (or 25 depending on config and airspeed I think) still protected? When alpha prot is active is it possible to pitch up to more than the maximum pitch limit? The diagram would suggest yes.

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    $\begingroup$ It may be they didn't bother detailing the behaviour because the aircraft won't have enough power to climb as steep and therefore will pitch down on the alpha protection alone anyway. $\endgroup$ – Jan Hudec Nov 9 '18 at 20:49
  • $\begingroup$ When you fly empty and fast (say 230kt+) and then pull up quickly you can pull 2.5 gs (load protection) and if you then manage to get the angle of attack high enough to trigger the alpha protection you could have the alpha protection active with enough excess energy to pitch to a high pitch angle. Pitch rate will be limited by alpha max then of course.... And at least in my flight simulator I can actually do that dynamically. I tested two commercially available flight sims for this, both got me to 30 degrees of pitch well before reaching actual low speed conditions where I run out of energy. $\endgroup$ – Jan Nov 9 '18 at 21:06
  • $\begingroup$ But yes, the alpha protection does also factor in the speed trend and pitch as far as this video suggests: youtube.com/watch?v=9fqy8uPzW90 (awesome video by the way, 9:12 for alpha protection) So the alpha protection might force the nose down enough $\endgroup$ – Jan Nov 9 '18 at 21:10
  • $\begingroup$ Hi Jan. I tweaked the title of your question to try to better summarize what you're asking. Feel free to Edit further or to roll back the edit if you feel my edit changed your intent in any way. $\endgroup$ – a CVn May 28 '19 at 14:45

In normal law « Alpha prot » has the highest priority, if AOA is less than alpha limit, teta (pitch angle) is limited between +25 and -15 at long run. At long run, since in emergency descent you are allowed for a short time to go beyond - 15° pitch down, to do that you need to pitch down the side stick very quickly after having engaged a steep roll.

If AOA protection is active, I don’t see how you can exceed 25°or 30° pitch up, since the FBW will pitch down the aircraft to follow the AOA protection.

  • $\begingroup$ The fundamental question is: does the AOA protection control angle of attack or does it control pitch and speed (trend)? If it does control AOA and nothing else it it physically possible to fly at 30° nose up and be at an angle of attack where the alpha protection kicks in and with a good enough thrust to weight ratio and a high speed (barely enough to fly above alpha protection) the protection would just follow your alpha command and since there is excess energy it could keep following that AOA and pitch above 30°. Unless there is an extra control loop on pitch angle. $\endgroup$ – Jan May 29 '19 at 6:23
  • $\begingroup$ Alpha protection is the highest protection, but lower priority protections will be followed if not contradicting higher priority. So the pitch CANNOT BE MAINTAINED ABOVE 25° for more than few seconds $\endgroup$ – user40476 May 30 '19 at 10:05

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