Doolaga,
I was able to find that the AOA triggering ALPHA FLOOR is 9.5 degrees in CONFIG 0; 15 degrees in CONFIG 1,2; 14 degrees in CONFIG 3; and 13 degrees in CONFIG FULL from the FCOM 1.27.20 P4. I don’t know if this is an oversimplification of the AOA that triggers ALPHA FLOOR or not. I am sure that ALPHA PROT is not based purely on AOA, but I have not been able to find any specific values regarding the triggering of ALPHA PROT. The following text is from an old Airbus publication that explains the flight control system laws with more detail than the FCOM (the same one quoted by atomic).
The aim of the law is to stabilize as quickly as possible at Alpha-max without any significant overshoots in Alpha. A pure alpha command and control law would arrive rapidly at Alpha-max, but it would then force the aircraft into a phugoid motion with the possibility of significant overshoots of Alpha-max. Therefore, a speed feedback is introduced to provide phugoid damping and an improved trajectory. This speed feedback associated with a well chosen gain permits Alpha-max to be safely reached in a minimum time.
Alpha protection can also be entered at high speed when it gives protection at the buffet boundary. Here, the aim is to allow the pilot to use all the available maneuvering capability while staying outside the deterrent buffet and countering any tendencies to pitch up. The high-speed stall occurs at much lower Alpha than the Alpha-max adopted as the low-speed limit, and Alpha-prot and Alpha-max are shifted down as a function of Mach when in the clean configuration. Thus, full back stick will result in the aircraft stabilizing at the buffet boundary with a small margin to the deterrent buffet. Because the margin is tiny, a small pitch-down pre-command is introduced progressively at a given Alpha between Alpha-prot and Alpha-max (function of Mach) to prevent dynamic overshoots into the deterrent buffet with rapid entries into Alpha protection at high Mach.
The engineers at Airbus have spent a considerable amount of time and effort designing a control system that enables the pilot to extract the maximum performance with regard to aerodynamic and structural limitations in the minimum amount of time. The control laws seem to be very well thought out. I know that abrupt high speed and low speed maneuvers typical of the type used to prevent CFIT or a mid-air collision, have been considered. I am sure that any additional details regarding the control laws are well beyond my ability to comprehend, and probably proprietary anyway.
I have always considered Alpha Floor a mode of the Autothrust system, and Alpha Prot a mode of the flight control system. So in my mind, they are two completely separate systems that work together. As far as your question of being able to encounter Alpha Floor but not Alpha Prot, my guess (and it is only a guess) is that you would first encounter Alpha Prot and second Alpha Floor. Depending on the initial conditions, and the rate of stick movement, the limitations due to G load or pitch attitude, may be reached prior to Alpha Prot and Alpha Floor.
Enjoy flying the Airbus, it is really an amazing aircraft. Remember, that even after you complete your training, there is so much to learn about this piece of equipment. Forums such as this are a great help. Sometimes your question about a system will get a response from the engineer who was involved in the design of that system.
Regards,
The Kid