History of the Flight
On 24 November 2019, an Airbus A321-231 (registration G-EUXJ) operated a commercial passenger flight from Glasgow Airport to London Heathrow. The flight crew, on the fourth day of a short-haul duty period, had operated A319, A320, and A321 aircraft during the previous three days. During passenger boarding, the commander allowed a couple of passengers to visit the flight deck. Later, while entering takeoff performance data into the Flight Management and Guidance Computer (FMGC), a senior cabin crew member requested another visitor; the commander ignored the request but reported possible distraction.
The takeoff was planned from the full length of Runway 05 with surface wind 080° at 5 kt, visibility 2,800 m in drizzle, cloud broken at 400 ft, temperature 8°C, and a wet runway. The required performance settings included flap 1, a flex temperature of 49°C, a non-standard acceleration altitude of 1,070 ft, and takeoff speeds V1 139 kt, VR 147 kt, and V2 151 kt.
After pushback at 1803 hrs and receipt of the final load sheet at 1808 hrs, the aircraft taxied to the runway. A request from ATC to depart from an intersection was later cancelled. The flight crew completed the before takeoff checklist and began the takeoff roll.
The Incident
During the takeoff roll, both pilots sensed the aircraft was not accelerating as expected. At approximately 100 kt, the co-pilot remarked, "this does not feel right, have we got enough power." At 137 kt, just before V1, the commander advanced the thrust levers to TOGA (Takeoff Go-Around) power. The aircraft rotated in the last 900 m of the runway and crossed the upwind end at 276 ft. The flight continued to Heathrow without further incident.
After takeoff, the crew realized they had entered a flex temperature of 79°C instead of the required 49°C.
Recorded Information
Flight data provided by the operator showed the takeoff profile; the actual acceleration was lower than the expected profile.
Crew Actions and Findings
The commander reported that during performance data entry, the pilot flying reads figures from a printed calculation, the pilot monitoring enters them into the Multipurpose Control and Display Unit (MCDU), and the pilot flying then checks the entries. The commander was uncertain whether he read "79°" or the correct "49°" and whether the co-pilot inadvertently pressed the adjacent '7' key instead of '4'. He speculated that he might have been focusing on the non-standard acceleration altitude rather than the flex temperature when checking. A call from the cabin crew may have contributed to the error or its detection failure.
Subsequent standard procedures—including pre-start checks, before takeoff checks, and the Flight Mode Annunciator (FMA) review during takeoff—required reading the flex temperature but did not involve cross-referencing with the original source data. The commander later noted that a flex temperature of 79°C was unusual for an A321 but typical for an A319, which the crew had flown earlier in their tour.
Previous Events
The AAIB referenced a similar incident in 2017 involving a Boeing 737-800 (C-FWGH) where an incorrect outside air temperature was entered, leading to a takeoff accident. The AAIB had previously issued a Safety Recommendation to develop certification standards for a Takeoff Acceleration Monitoring System.
Analysis
The investigation concluded that the flight crew inadvertently entered a flex temperature of 79°C instead of 49°C. The error likely resulted from a combination of brief distraction and the presence of a non-standard acceleration altitude. The subsequent checks did not require reference to the source data, and the selected flex temperature, though unusual for the A321, was not unusual for the A319 operated earlier. The crew correctly recognized insufficient power and applied TOGA power before V1.
Safety Actions
The operator issued a safety notice to all flight crews highlighting this and previous events, emphasizing the importance of avoiding distractions during takeoff performance data loading. The operator is also reviewing its data entry and checking procedures to improve error detection.