What happened
On 6 December 2019, an Air Algérie Boeing 737-800, registration 7T-VJM, was on final approach to runway 25 at Paris-Orly. While the aircraft was at approximately 477 ft—just 13 ft below the decision altitude—the air traffic controller ordered a go-around. This instruction was prompted by a Runway Incursion Monitoring and Collision Avoidance System (RIMCAS) warning, which had been triggered by a bird-control vehicle near the runway.
During the missed approach, the crew applied high thrust and a nose-up attitude, causing the aircraft to climb rapidly. However, as the crew initiated a left turn to follow the missed approach path, the bank angle exceeded 35°, triggering a "BANK ANGLE" alert. The aircraft's speed decreased, and the altitude began to drop below the target 2,000 ft level.
When the controller subsequently instructed the crew to climb to 3,000 ft, the crew modified the altitude selection on the Mode Control Panel. This action triggered a mode reversion to Vertical Speed (V/S) mode, which captured the aircraft's instantaneous descent rate of approximately 1,100 ft/min as the new target. This led to a continued descent to roughly 1,300 ft, accompanied by "DON'T SINK" GPWS alerts and a period of high-speed flight exceeding flap placard limits. The crew eventually stabilized the aircraft and performed a second approach successfully.
The investigation
The BEA investigation focused on the sequence of events following the RIMCAS activation and the management of the aircraft's automation. The investigation established that the RIMCAS warning was erroneous; a recent relocation of a holding point had not been updated in the system configuration, causing the system to flag a vehicle that was actually outside the runway safety area.
Investigators also examined the flight management of the Boeing 737-800 during the transition from manual to automated flight. The analysis highlighted how the Flight Director (F/D) command bars and the transition into V/S mode contributed to the flight path deviation. The investigation also reviewed the impact of the "startle effect" on the crew's workload and decision-making.
Findings
Several factors contributed to the altitude deviation:
- Erroneous RIMCAS activation due to unupdated system parameters following runway maintenance.
- The startle effect caused by an unexpected go-around instruction at a very low altitude, which increased crew workload and disrupted coordination.
- Inappropriate management of automation, specifically the crew's decision to follow Flight Director cues without verifying that the underlying flight modes (such as the V/S mode reversion) were compatible with the intended flight path.
- A lack of system consistency checks, as the aircraft automation did not alert the crew that the new altitude selection would result in a descent-oriented vertical speed target.
- High workload resulting from the combination of the sudden maneuver, the high bank angle, and the activation of multiple cockpit warnings.