Large Transport; Low Wing; 2 Turbojet Eng
Flight Crew Air Transport Pilot (ATP)
Deviation - Altitude Overshoot; Deviation - Speed All Types; Inflight Event / Encounter Weather / Turbulence
Weather
We had been descending on the Eagul 6 Arrival into PHX. During the descent; we experienced light to moderate chop as we descended below 27;000 feet and I made sure that our flight attendants had taken their seats. After we contacted Phoenix Approach we were told that the rides would smooth out below 12;000 feet. As we below 12;000 feet the turbulence did not abate. Descending out of 8;000 we heard the preceding aircraft report continuous moderate chop descending out of 6;500 feet. As we descended through that altitude we also started to experience continuous moderate turbulence. The controller directed us to descend to and maintain 4500 feet. We were at as speed of 210 KIAS in a clean configuration as we descended out of 4800 feet. We flew into what I can only describe as severe turbulence. The autopilot disconnected; the speed dropped very suddenly to 170 and the aural warning 'stall; stall' went off. I pushed the nose down smoothly to break the stall; but the airspeed had already shot back over 260 KIAS and just as quickly the speed dropped back to 190 KIAS before settling between 200 and 240 KIAS. We also found ourselves at an altitude of 4200 feet. My First Officer (FO) told approach control that we had descended below 4500 feet and had experienced severe turbulence. The controller then gave us a left turn to a heading of 180; slow to 180; and maintain 4000 feet. I asked my FO to turn the autopilot back on. As soon as he did we flew into round two of the severe turbulence. The autopilot again disengaged but this time we did not get a stall warning. As we had been slowing I was going to ask for 'Flaps 1'; but the speed was fluctuating between 190 and 240. As we were cleared for the visual approach I elected to direct the FO turn off the flight directors and bring up the Flight Path Vector (FPV) display. I also asked for gear down to slow the aircraft. When we contacted Phoenix tower; we were told that we were only two miles in trail of the preceding aircraft and we made an S-turn for spacing with the controller's approval. The remainder of the approach was uneventful.The forecast called for clear skies in Phoenix with no hint of inclement weather. Our first warning of moderate turbulence came from a report from the preceding aircraft. We had our radar on and we did not depict any rain in the area. Our first hint that we were about to fly into severe turbulence was when we hit the turbulence. I am not sure it could have been avoided under the circumstances. Weather forecasting is not always completely accurate as we know. Unplanned weather events are not as uncommon as we would like them to be but they are a fact of life in aviation. We were also unable to avoid the turbulence using radar; as there were no returns showing. I'm not sure that we could have avoided the event. However; having just completed [advanced training] recently; I found that both the stall and unusual attitude scenario were helpful in recovery from the event.
A320 Captain reported severe turbulence on approach to PHX followed by an uneventful landing.