Description

On 27 September 2019, an Airbus A320 (EC-MKO) being operated by Vueling on an international passenger flight from London Gatwick to Barcelona as VLG 19ZN and an Embraer 145 (F-HRAM) being operated by Aero4M on a non revenue positioning flight from Castres-Mazamet, France to Barcelona as AEH993F came within 0.8 nm laterally when only 200 feet apart vertically as they converged on the same waypoint at similar altitudes in day IMC despite both apparently following their TCAS RAs.

Investigation

Once notified of the event, an Investigation was commenced by the Spanish Commission for the Investigation of Accidents and Incidents (CIAIAC). Due to a delay in the reporting of the event to the Commission, relevant data from both the CVR and the DFDR had been overwritten. However, relevant data from both aircraft QARs were available to the Investigation as were relevant recorded ATC radar and voice communications data.

The 49 year-old A320 Captain had a total of 11,786 hours flying experience of which 10,259 hours had been on type and his 23 year-old First Officer had a total of 815 hours flying experience all but 165 hours of which had been on type. The 32 year-old Embraer 145 Captain had a total of 2,493 hours flying experience of which 1,193 hours had been on type and his 28 year-old First Officer had a total of 3,928 hours flying experience of which 177 hours had been on type. The 50 year-old Barcelona ACC sector Executive Controller involved had held a licence for 19 years and had gained all of his subsequent experience there. The 53 year-old Planning Controller had held a licence for 30 years and had also gained all of his subsequent experience at the unit.

What Happened

The A320 was cleared for a PUMAL 1L STAR to be followed by the CLE1W Transition to an approach to runway 25R and the Embraer 145 was cleared for an ALBER1W STAR to be followed by the same Transition to a runway 25R approach.

Initially, both aircraft had been instructed to descend to FL 100 by the sector T1W controller. Then, ten minutes prior to the eventual conflict, the same controller cleared the A320 to fly in an approximately southerly direction direct to waypoint BL443 (see the illustration below) and on receipt of the readback then instructed the Embraer 145 to also fly direct to waypoint BL443 (an approximately south southwesterly track) and then follow the Transition but its crew only read back the first part of this instruction and omitted mention of being also cleared to continue on the Transition. The controller then instructed the A320 to descend to 5000 feet QNH and, on receipt of this readback, then cleared the Embraer 145 to descend to FL 080 (also read back correctly) and then the A320 to reduce speed to 250 knots.

The chart which included the CLE1W Transition which both aircraft were being positioned for with waypoints BL443, BL439 and BL435 within the yellow circle. [Reproduced from the Official Report]

With three minutes to go before the conflict, the T1W controller then instructed the Embraer 145 to descend to 6000 feet and then added that they should fly direct to waypoint BL435, both these clearances being correctly read back. Half a minute later, he instructed the A320 to reduce to “minimum clean approach speed” and transferred it to the sector F25W frequency. When the flight checked in with the F25W controller, that controller then instructed it to continue descent to 2,300 feet QNH. The T1W controller then instructed the Embraer 145 to stop descent at FL 070 and when the crew reported they were just reaching it, he instructed them to reduce speed to 210 knots.

Shortly after this, the T1W controller asked the F25W controller to instruct the A320 to increase its rate of descent (which he subsequently did) and then instructed the Embraer 145 to immediately turn right (the long way round) onto radar heading 070°.The crew asked for this instruction to be repeated and the controller then instructed them to turn immediately left onto heading 070°. By this time, the crew reported having the potentially conflicting A320 ahead in sight and, both being “uncomfortable” with the controllers instruction which seemed likely to reduce rather than increase separation, they again requested confirmation that a left turn was required and when this was given, they began the turn only to stop it when a further requested confirmation of the turn instruction was followed by “maintain current heading”.

Both aircraft were now converging on almost the same position with the Embraer 145 level at FL 070 and approaching the A320 as it crossed in front of them at FL 070 having not yet begun descent from that level as cleared. Shortly afterwards, the A320 reported a TCAS RA ‘DESCEND’ to the F25W controller at which point it was 0.9 nm away from the Embraer 145 and 200 feet below it. Six seconds later, when the Embraer 145 was instructed to turn into heading 060°, its crew acknowledged having also received a TCAS RA ‘DESCEND’ adding that they now had visual contact with the traffic. This exchange occurred at the closest point of approach with the two aircraft 0.8 nm apart as the A320 descended through FL 068 and the Embraer 145 remained level at FL 070.

The sector T1W controller subsequently stated that his actions had been founded on a potential conflict between the Embraer 145 and a third aircraft approaching the Transition from the west. He decided to avoid this problem by instructing the Embraer 145 to fly directly to waypoint 435 and descend to 6000 feet, since the A320 from the north was descending to 5000 feet at a normal rate of descent. However, having transferred the A320 to the F25W sector, he realised that it had reduced its rate of descent after being instructed to reduce speed so he had instructed the Embraer 145 to stop its descent at FL070, thinking that the vertical separation would be sufficient. When it became clear that it would not be, he had “instructed the Embraer 145 to conduct an evasive manoeuvre by turning left to heading 070 but it reacted late and requested confirmation of the left turn”. He stated that it was this crew’s delay in turning left that had led to the prescribed minimum separation being breached.

Why It Happened

Having examined the available evidence, the Investigation observed, in summary, as follows:

• The Embraer 145 crew did not read back the second part of their clearance to fly direct to waypoint BL443 which was to “continue with the Transition”. Since this omission was not challenged by the T1W controller, it was not known whether the crew had registered this part of the instruction.
• The T1W controller’s subsequent instruction to the Embraer 145 to fly direct to waypoint 435 was not agreed with the controller of the F25W sector which was in direct conflict with the related handover requirement to this effect which was included in the ANSP’s Barcelona OM.

The formal determination of the Cause of the loss of separation between the two aircraft was “improper planning and execution of the approach sequence by the controller in sector T1W”.

Two Contributory Factors were also identified:

• The sector T1W controller did not correct an incomplete acknowledgment by the crew of AEH993F to fly a Transition.
• The sector T1W controller did not coordinate with the final sector (F25W) before instructing AEH993F to fly direct to point BL435.

Safety Action taken by the ENAIRE, the ANSP, was noted as having been to recommend that their internal investigation report on the event should be sent to the Barcelona TMA Training Department for potential inclusion in their annual “Review of Regulatory and Technical Changes” and that this had been approved and the next one would be held in the fourth quarter of 2020.

The Final Report of the Investigation was approved on 29 April 2020. No Safety Recommendations were made on the basis that the action intended to be taken by the ANSP Training Department was “deemed to be adequate”.

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