What happened
On October 6, 2019, a Boeing 737-800, registration SP-ENV, was descending through Flight Level 150 toward Flight Level 130 within the Paris controlled airspace (TMA LFPG) while en route to Charles de Gaulle Airport. During the descent, the aircraft's Airborne Collision Avoidance System (ACAS) issued a "TRAFFIC" alert, notifying the crew of a potential separation infringement. Shortly thereafter, the system issued a Resolution Advisory (RA) command of "CLIMB."
In response to the RA, the pilot ceased the descent and initiated a climb. The maneuver continued until the ACAS provided the "DON'T DESCENT" and subsequently the "CLEAR OF CONFLICT" advisories. Following the resolution of the conflict, the crew notified Air Traffic Control (ATC) of the ACAS RA. The controller informed the crew that the conflicting aircraft had departed from Paris-Orly (LFPO) and had been cleared to climb to Flight Level 110. The crew maintained a standard descent rate of 1,000 feet per minute following the encounter. According to French authorities, the minimum separation requirements—2.25 NM horizontally and 1,700 feet vertically—were not breached by SP-ENV.
The investigation
The investigation examined the sequence of events involving the Boeing 737-800 and the interaction between the ACAS systems of the two aircraft. The inquiry established the flight path of the aircraft, the specific ACAS alerts received by the crew, and the separation parameters maintained between the two aircraft during the encounter.