A Vueling Airbus A320-200, registration EC-MKO performing flight VY-7835 from London Gatwick,EN (UK) to Barcelona,SP (Spain) with 185 passengers and 6 crew, was descending towards Barcelona cleared to fly the standard arrival route PUMAL1W and CLE1W transition to runway 25R in contact with Barcelona Area Control Sector's F25W. The aircraft had been instructed to descend to 5000 feet and was nearing waypoint BL443.
An Amelia/Aero4M Embraer ERJ-145, registration F-HRAM performing flight NL-993 from Castres (France) to Barcelona,SP (Spain) with 3 crew, was on approach to Barcelona having received clearance to follow the standard arrival route ALBER1W with CLE1W transition to runway 25R in contact with Barcelona Area Control Sector T1W. The aircraft was cleared to fly direct to BL443 and follow the transition, however, the crew only read back to fly direct to BL443. The aircraft was subsequently cleared to descend to 6000 feet, 30 seconds later the aircraft was cleared to fly direct to BL435. The aircraft was subsequently restricted to stop the descent at FL070 upon reaching.
As result both aircraft were on converging trajectories at similiar altitudes (The E145 at 7000, the A320 at 6800 feet MSL), TCAS resolution advisories were issued for both aircraft. Spain's CIAIAC reported the separation reduced to 200 feet vertical and 0.8nm horizontally.
The CIAIAC released their final report concluding the probably causes of the incident were:
The investigation has determined that the loss of separation between the two aircraft was caused by improver planning and execution of the approach sequence by the controller in sector T1W.
Contributing to the incident is the fact that the sector T1W controller:
- did not correct an incomplete acknowledgment by the crew of AEH993F to fly a transition, and
- did not coordinate with the final sector (F25W) before instructing AEH993F to fly direct to point BL435.
The CIAIAC summarized the testimony of the captain of the A320:
During the RNAV approach with the CLE1W transition to RWY 25R, they were instructed to descend to 2300 ft, and while flying between points BL435 and BL427, descending through FL070 for 2300 ft and at the airplanes minimum clean speed, they received a TCAS TA, which then turned into a TCAS RA descend. The crew reported the TCAS RA on the frequency and executed it as indicated by the resolution. A few seconds later, they were clear of conflict, so they reported they were continuing their descent to 2300 ft, as they had been instructed. Subsequently, the controller apologized and asked if they were going to file a report, to which they answered affirmatively.
The CIAIAC summarized the testimony of the captain of the E145:
They were cleared to execute the CLE1W transition to the Barcelona Airport. Crossing through BL4435, they were cleared to descend to 6000 ft, and as they started the descent, they were re-cleared to FL070. In his opinion, he did not feel comfortable with ATCs instructions. A few seconds later, they saw a traffic approaching from their right on TCAS, which they had in sight. The controller vectored him to his left, heading 070. He thinks it was for conflict avoidance, but the other aircraft was on a converging track. The crew started turning left and immediately requested confirmation of the assigned heading, since neither the first officer nor the captain agreed with it. They again felt that the controller was a little disoriented. He instructed them to maintain heading, which they did. F-HRAM saw the other traffic cross from right to left, and at that point they received a TCAS RA. The first officer held the course manually and they were carrying out the TCAS RA descend, which lasted 2 or 3 seconds, during which they lost under 100 ft. The captain then informed ATC that it had been a dangerous situation. The crew were fully aware of the situation, the traffic and the environment at all times during the incident.
The CIAIAC summarized the testimony of the T1W sector controller:
He described the sequence that led the aircraft to converge at point BL443: first, VLG19ZN, then AEH993F, and lastly another aircraft with callsign VLG8477. Upon realizing that AEH993F and VLG8477 would converge at said point, he decided to instruct AEH993F to fly direct to point BL435, and he instructed it to descend to 6000 ft, since VLG19ZN was descending to 5000 ft at a normal rate of descent. So he transferred VLG19ZN to sector F25W as it was passing through FL075. He quickly realized that VLG19ZN reduced its rate of descent, so as a result he instructed AEH993F to stop its descent at FL070, thinking the vertical separation would be sufficient. However, VLG19ZN, despite being cleared to lower altitudes, maintained FL070. Therefore, the controller instructed AEH993F to conduct an evasive maneuver by turning left to heading 070, but it reacted late and requested confirmation of the left turn. He insisted and the crew asked again, which led6 to the prescribed minimum distances being breached. Finally, AEH993F reported having the traffic affecting it in sight to its left, so he instructed it to maintain its current heading, although it should have been turning and following7 the TCAS RA.
The CIAIAC summarized the testimony of the executive controller of sector F25W:
He stated that he received two aircraft (VLG19ZN and AEH993F) from the feeder sector (T1W) that had already lost separation. VLG19ZN was cleared to descend to 5000 ft, but that it had not yet left FL070 and was at point BL435. AEH993F was flying north to south, steady at FL070, converging with VLG19ZN, which reported a TCAS RA.
The CIAIAC summarized the testimony of the planning controller of sector F25W:
He stated that the traffic at the time was moderate or intense and that he was doing the tasks of both the planning and queue manager. While the scale is sufficiently broad to be able to validate the sequence numbers and see if any have to be changed, the area where the incident occurred is a jumble of overlapping labels where it is impossible to control anything. He was surprised to see AEH993F flying to point BL435, since that point is not used often. He mentioned this to the executive controller in his sector.
Just then, the executive controller in sector T1W called sector F25W to request that VLG19ZN increase its rate of descent. The two aircraft involved were on different frequencies at the time: VLG19ZN on the frequency of sector F25W and AEH993F on the frequency of sector T1W. The executive controller in sector T1W explained that this was because VLG19ZN was cleared to descend to 5000 ft, so he transferred it to sector F25W.
AEH993F was flying to point BL435 to separate from another traffic [VLG8477] in sector T1W. It was cleared to descend to 6000 ft. VLG19ZN did not descend at the rate expected by sector T1W, and he heard how the executive controller warned sector F25W in order to have it increase its rate of descent. At the same time, sector T1W stopped the descent of AEH993F at FL070.
Separation between the two aircraft was lost, and even though sector T1W made AEH993F turn, the distance between the two, I seem to recall, fell to 0.8 NM. Both aircraft received TCAS RA.
The CIAIAC analysed:
The following facts are relevant and decisive in the lead-up to the loss of separation between the two aircraft:
1) When AEH993F was instructed to fly direct to the BL443 to continue with the transition, its crew only acknowledged fly direct BL443. Since they did not acknowledge the second half of the instruction, it is impossible to know if they were aware of the totality of the instruction given.
2) The above error in the acknowledgment was not corrected by ATC, meaning it was very likely that the crew of AEH993F did not know what would happen after point BL443 and were expecting to receive subsequent instructions, unsure if they would fly the transition. This error resulted in a breach of the provisions in Regulation (EU) No 923/2012, section SERA.8015 e) 3), since the controller did not ascertain that the clearance or instruction had been correctly acknowledged by the flight crew and did not take immediate action to correct any discrepancies revealed by the read-back.
3) In order to keep AEH993F from converging with another aircraft at point BL443, the controller instructed AEH993F to fly direct to a different point of the transition (TRAN CLE1W), specifically, to point BL435. As specified in point 18.104.22.168.5.2.1 (page 117) of the LECB Operations Manual, Annex B: Unit-Specific Procedures, as well as checklist SOP 09, both procedures were breached by not coordinating with the final sector (in this case, F25W) before clearing the aircraft to fly to point BL435.
In addition, the lack of coordination with sector F25W notwithstanding, this instruction is considered inappropriate since it made AEH993F and VLG19ZN converge at point BL435 at very similar altitudes. It has been deemed that the controller in sector T1W correctly detected the conflict but he implemented a faulty plan and executed it improperly, resulting in the loss of prescribed separation between the two aircraft.