Airbus A321 F-GTAN: Undetected Speed Loss and Alpha Protection Activation During Approach

Incident Overview and Context On July 20, 2012, at approximately 15:00 UTC, an Air France Airbus A321 with registration F-GTAN was operating a scheduled passenger flight from Bordeaux to Paris Charles de Gaulle. The flight crew consisted of a pilot flying (PF) and a pilot monitoring (PM). During taxi, the SEC1 (Spoilers Elevator Computer) was declared inoperative, and the crew followed the associated ECAM procedure, which required that spoilers not be used during the flight. ## Descent and Mixed Mode Situation During the radar-guided approach, the aircraft was in clean configuration with AP1, A/THR, and flight directors engaged. The crew descended at 250 kt in OPEN DES mode. As the aircraft descended from FL90 to FL60, air traffic control requested a short exit and a descent to 4,000 ft, stable by 18 to 20 NM. Although the existing descent profile could have met this constraint, the PF decided to expedite the descent. Because spoilers were unavailable, the PF moved the thrust levers to IDLE, which disconnected the A/THR. The PF did not announce this action, and the PM was unaware of the disconnection. ## Speed Loss and Protection Activation At 15:12:32 UTC, the speed fell below the selected 220 kt while ATC announced traffic. Both crew members looked outside to search for the traffic. With thrust at IDLE and A/THR disconnected, the autopilot maintained altitude by increasing pitch and angle of attack, causing speed to decrease. At 15:13:05 UTC, the autopilot disconnected on incidence criteria, and Alpha PROT (high-incidence protection) activated at 177 kt, which was 26 kt below VLS. The PF advanced the thrust levers to CLB and applied back pressure on the sidestick as the aircraft began to descend. Speed reached a minimum of 172 kt (VLS - 31 kt) with a descent rate of approximately 1,000 ft/min. ## Recovery and Landing At 15:13:15 UTC, as thrust began to build, the PF set the levers to FLEX/MCT and applied maximum back pressure. The aircraft reached a minimum altitude of 3,840 ft QNH. As thrust stabilized near 94%, speed increased and the aircraft climbed. The PF then applied nose-down input for about three seconds to counter the pitch-up moment, which inadvertently deactivated Alpha PROT. The crew then stabilized the aircraft, resumed the approach, and landed without further incident. ## Contributing Factors The incident involved a mixed mode situation (AP ON, A/THR OFF), which is not recommended by the manufacturer because the autopilot compensates for insufficient thrust by increasing pitch at the expense of speed. The crew's focus on searching for announced traffic reduced monitoring of primary flight parameters, particularly speed. The operator had previously identified this risk and issued a safety flash in February 2012 warning about the mixed mode trap and the importance of crew coordination and instrument monitoring.