Flight Crew Air Transport Pilot (ATP); Flight Crew Instrument; Flight Crew Multiengine
Flight Crew Total 6000
Situational Awareness
Deviation - Altitude Excursion From Assigned Altitude; Deviation - Speed All Types; Deviation - Track / Heading All Types; Deviation / Discrepancy - Procedural Clearance; Deviation / Discrepancy - Procedural Published Material / Policy
Flight Crew Became Reoriented; Flight Crew Returned To Clearance
Human Factors
I was PF (Pilot Flying); descending via the [charted arrival]. Due to a tailwind; I extended full speed brakes in order to make the altitude and speed restriction. Slightly before ZZZZZ; with the restrictions met; I selected speed 225 (to allow for flap extension); requested Flaps 1; and stowed the speed brakes. The AP (autopilot) rolled the aircraft into a right bank to make the slight turn onto the next leg of the STAR. The aircraft immediately entered Alpha-Floor protection; disconnecting the AP and setting thrust to TOGA; which resulted in a climbing right turn with increasing pitch. After realizing; with helpful input from the PM (Pilot Monitoring); what was causing the deviation from planned flight path; attitude; and altitude; I recovered the aircraft to wings-level flight; ensured safe airspeed for our configuration; disconnected the auto-thrust; corrected to course; began a descent; re-engaged the AP; and continued on the STAR ground track. Total altitude gain was slightly over 1000 feet and lateral deviation from STAR was approximately 1/4 mile. ATC queried us and the PM replied that one of our protections had engaged; causing the deviation. ATC put us on a heading and gave us a descent to 8000 feet. The remainder of the approach and landing was uneventful. I assume that this event occurred because the speed brakes were still retracting when the aircraft banked into the turn. [The flight manual] discusses ensuring an adequate speed margin if speed brakes are extended before beginning a turn; in order to prevent the activation of Alpha-Floor protection.Even before this event; I was concerned that our training inadequately addresses the A321's behavior with speed brakes extended with respect to the VLS hook [minimum selectable airspeed] and Alpha-Floor protection. You hear things like 'the 321 is hard to slow down'; but the details of why and recommended techniques of managing descents in the 321 are not well covered. This aircraft was relatively light; and I thought we were carrying plenty of speed. I retracted the speed brakes in what I thought was plenty of time to avoid Vls issues and got a notch of flaps down. I was completely taken by surprise at the activation of Alpha-Floor protection. I recommend training focus more attention on this situation and techniques for anticipation and avoidance.In the future I will stay even farther ahead on descents to avoid instances where speed brake extension can put the aircraft close to Alpha-Floor protection engagement. In addition; I realize I could have stayed at 230 with flaps up as long as I had the speed brakes up earlier. I was thinking of the upcoming 210 restriction at ZZZZZ1; but remaining at 230 through ZZZZZ would have been more procedurally correct.
A-321 First Officer reported track and altitude deviations occurred on the arrival when Alpha-Floor protections were triggered in a turn while retracting speed brakes.