What happened
On September 27, 2019, at 10:04 UTC, a loss of separation occurred between a Vueling Airbus A320, registration EC-MKO, and an Aero4M Embraer 145, registration F-HRAM, approximately 17.4 NM northeast of Barcelona-El Prat Airport. Both aircraft were performing instrument approaches to runway 25R.
The Airbus A320 was descending via the PUMAL1W arrival. The Embraer 145 was following the ALBER1W arrival. During the approach, the air traffic controller for sector T1W instructed the Embraer 145 to fly direct to waypoint BL443 and proceed with the transition. However, the crew only read back the instruction to fly direct to the waypoint, omitting the transition instruction. The controller failed to correct this incomplete readback.
To avoid conflict with a third aircraft, the controller subsequently instructed the Embraer 145 to fly direct to waypoint BL435. This instruction caused the two aircraft to converge on the same waypoint at very similar altitudes. Both aircraft received TCAS Resolution Advisories (RA). Radar data confirmed that the minimum separation reached was 0.8 NM horizontally and 200 ft vertically at flight level 070.
The investigation
The CIAIAC investigation focused on the sequence of instructions provided by the T1W sector controller. The investigation established that the controller failed to ensure the Embraer 145 crew had correctly understood the full transition instruction. Furthermore, the investigation found that the controller did not coordinate with the adjacent F25W sector before authorizing the Embraer 145 to fly direct to waypoint BL435.
While the controller attempted to resolve the conflict by requesting the Airbus A320 to accelerate its descent and providing various heading instructions to the Embraer 145, these actions were insufficient to prevent the loss of separation. The investigation also noted that the controller's plan for the Embraer 145 actually facilitated the convergence with the other aircraft.
Findings
- The primary cause of the loss of separation was the incorrect planning and execution of the approach sequence by the T1W sector controller.
- The controller failed to correct an incomplete readback by the Embraer 145 crew regarding the transition instruction.
- The controller failed to coordinate with the F25W sector before issuing the instruction for the Embraer 145 to fly direct to waypoint BL435.
- There were no injuries to the crew or passengers, and no damage was sustained by either aircraft.