A320 / B738, Barcelona Spain, 2022
A320 / B738, Barcelona Spain, 2022
On 29 April 2022, an Airbus A320 and a Boeing 737-800 came into close proximity at Barcelona at night - 247 metres laterally and 44 feet vertically - after the A320 received landing clearance for runway 02 and the 737 was then given takeoff clearance on runway 06R. Both aircraft were following ATC instructions issued shortly after runway use had changed from daytime (parallel runways in use) to nightime configuration (near-intersecting runways in use). The landing clearance was issued contrary to procedures by a controller who had failed to reconfigure their position when runway use changed.
Description
On 29 April 2022, an Airbus A320 (EC-KLT) being operated by Vueling on a scheduled international passenger flight from Amsterdam to Barcelona as VY8307 and a Boeing 737-800 (EI-EPA) being operated by Ryanair on a scheduled international passenger flight from Barcelona to London Luton as FR7808 came into close proximity in night VMC when the A320 passed over runway 06R at 59 feet agl as the 737 was accelerating for the instructed immediate takeoff on that runway and only 285 metres from the A320 overflight track. Three seconds before the aircraft tracks crossed, the A320 was instructed to go around.
Investigation
The Spanish Commission for the Investigation of Accidents and Incidents (CIAIAC) carried out an Investigation using radar recordings and recorded A-SMGCS activations in the TWR.
The 40 year-old A320 Captain, who was acting as PF for the approach had been employed by the airline since 2019 .He had a total of “approximately 10,000 hours” flying experience including 6,935 hours on type all acquired since joining Vueling in 2010. He had been promoted to Captain in 2013. The 25 year-old A320 First Officer had a total of “approximately 1,800 hours” flying experience of which 1,350 hours were on type, all acquired since joining Vueling in 2018. Both pilots were based in Barcelona and therefore very familiar with the operation of the airport. The 36 year-old 737 Captain had been employed by the airline since 2009 and had a total of 9,268 hours flying experience all but 315 on type. The 30 year-old 737 First Officer, who was acting as PF for the departure but also covering radio communications whilst the Captain was in control of the thrust levers, had a total of 1,803 hours flying experience of which 1,350 hours were on type. The 32 year-old TWR controller had just 7 months experience as a controller, all gained at Barcelona after obtaining his ATC licence on October 2021. He had been working the final 90 minutes in position which would take him to the end of his 7½ hour shift which was due 20 minutes after the conflict occurred. The TWR 60 year-old TWR Supervisor had 22 years experience at Barcelona having been there since shortly after obtaining his ATC licence. He was rostered to work the night shift which started at 20 minutes after the conflict had occurred but had arrived more than half an hour early.
What Happened
The airport had routinely changed its runways-in-use twelve minutes prior to the near miss from the standard daytime configuration for the prevailing mean wind velocity using parallel runways 24R for arrivals and 24L for departures to the standard nightime configuration for those conditions using intersecting runways 02 for landings and 06R for departures. The most recent METAR ahead of the changeover gave the surface wind as 210°/3 knots and the visibility as in excess of 10 km with no cloud below 5,000 feet aal.
The TWR controller who took over responsibility for both runways in use after the change had prior to it been responsible only for departures from runway 24L with a second controller responsible for arrivals on runway 24R. The configuration change required manual modifications to the information display system at each controller position but these modifications were not completed by the controller who continued in position and took over control of both active runways. This oversight meant that the arrival runway selected (in green in illustration below) on the General Information Display was not changed so that times and distances to the threshold for inbound traffic on the controller’s display were longer than the actual times and distances.
Runway configuration before and after the change 12 minutes prior to the conflict. [Reproduced from the Official Report]
The controller failed to notice an illuminated caution on the General Information Display which should have alerted them to their error (see the illustration below). The departing 737 advised that it was ready for takeoff as it neared the 06R threshold and was cleared to line up. It was the seventh departure since the runway configuration had been changed. At this time, the A320, the fourth arrival since the configuration change, was 4.5 nm from the 02 threshold (but was showing 5.8 nm on the controllers incorrectly configured display system).
The General Information Display (VIG) still showing 24R as the arrivals runway. [Reproduced from the Official Report]
The controller asked the 737 if it could accept an immediate departure (as the seventh departure since the runway changes) whilst it was still on the parallel taxiway (position 2 on the illustration below) and on receiving confirmation immediately transmitted “cleared for rolling takeoff” (position 3) and received a readback with identical wording. At this time, the A320 was 2.9 nm from the 02 threshold with a landing aircraft ahead (but was showing 4.1 nm on the controller’s incorrectly configured display system).
The controller transferred an aircraft which had just landed on 02 to GND and informed the A320 to “expect late landing clearance one departure” (position 4) which was acknowledged. As the 737 began its takeoff roll on 06R without stopping, the A320 was 1.1 nm from the beginning of runway 02 (showing as 2.4 nm for the controller) and just 0.9 nm from crossing low over runway 06R. (position 5)
The tracks of both aircraft prior to the conflict point. [Reproduced from the Official Report]
Seven seconds after this (position 6) notification of a Level 2 conflict alert generated by the A-SMGCS (which the TWR Supervisor had activated earlier) appeared on the controller’s General Information Display with the A320 0.9 nm from runway 02 (showing as 2.1 nm for the controller) and 0.7 nm from crossing low over runway 06R. The 737 was 100 metres from the 06R threshold and accelerating through 26 knots ground speed. The controller took 7 seconds to acknowledge the conflict alert after it appeared and a further six seconds to instruct the A320, whose crew had just detected the accelerating 737, to go around (position 8). The A320 was less than 300 metres from crossing the runway 06R centreline and the 737 was 420 metres from the same point as it accelerated through 85 knots. Three seconds later, the A320 flew over runway 06R at 59 feet agl whilst still descending at 340 fpm as its crew read back the go-around instruction and began transitioning to it as the 737 was passing 97 knots and just 285 metres from the A320 crossing point. Minimum separation - 247 metres and 44 feet - occurred just after the actual/projected tracks had intersected.
The 737, whose crew had not seen the A320, continued their take off and rotated after 1,800 metres whilst the A320 carried out the missed approach and subsequently landed on runway 02 without further event. Only after the conflict was over did another controller in the TWR approach the position occupied by the runway controller involved and notice that the General Information Display runway button was still yellow, i.e. runway 24R was still incorrectly selected as the arrival runway.
The aircraft relative positions after the A320 had crossed over runway06R. [Reproduced from the Official Report]
Why It Happened
The direct cause of the conflict was clearly the error made by the TWR controller involved but the Investigation examined the context for this error in detail.
- The controller was interviewed and “provided the following data of interest to the investigation”:
- When the runway configuration was changed, “he had to modify the map and the zoom in order to see the whole of the ATZ (a 4 nm radius circle) and the runway 02 localiser”.
- He had considered that the departing 737 “was taxiing swiftly and that everything was running smoothly before the alarm was triggered”. He was unable to recall anything that he felt might be relevant happening before the conflict occurred.
- He recalled that the A320 had made its first call to TWR when 10 nm from touchdown whereas inbound traffic “usually calls at 4 nm”.
- He recollected looking outside and “seeing that the A320 was close but then checking the label and finding it was further away”.
- He remarked that “when the alarm went off, he was surprised” and that “with inbound traffic at 1.4 minutes or 3.5 nm, there is sufficient margin to clear a take-off from 06R”.
- He did not consider his workload had been high and did not regard a configuration involving intersecting runways as being particularly complex.
- The TWR Supervisor noted that the runway configuration change was complete when he began work and, after handover, he had begun his shift early by preparing his brief for the controllers about to begin work. A problem then arose which meant he had to call the electricians and had been doing so when the A-SMGCS violation occurred. He went over to the TWR controller’s position, saw the 737 taking off and that the controller “was busy coordinating the traffic he had instructed to go around” and had “not realised the seriousness of what had happened”. The TWR controller remained in position until his shift ended shortly afterwards and he went home.
- The GND controller was seated next to the TWR controller so they were able to talk to each other normally. The GND frequency was relatively quiet and having transferred the departing 737 to TWR, the GND controller “was able to listen to the communications (and) recalled that when he heard the taxiing traffic confirm they were ready for takeoff, he had told the TWR controller that there wasn't room”. He added that the TWR controller “had replied that there was (room) because (the A320) was 3 nm away” and he had responded by saying that “it was less than 2 nm away (but) had not insisted any further”.
- The A-SMGCS at Barcelona was a Level 2 system which could issue two RI-related alerts but in this case the way it was configured meant that the first activation (a visual-only warning) was omitted and a visual and acoustic ‘Violation’ was activated along with a red line which connects the two traffic units involved. However, the triggering of this violation was delayed.
- It was found from talking to ten Barcelona TWR controllers with unit experience ranging from 7 months to 22 years, including some qualified as an OJTI or as a TWR Supervisor, that they all considered that A-SMGCS Violation incursion alerts were frequently false and that they had all experienced such a false alarm within the last 7 days. Some of them estimated that “90-99% of Violations were false” and noted that the system which generated them had only been implemented approximately a year ago and they “felt it was immature”.
- Visibility of runways 02 and 06R from the TWR controller’s position was found to be such that traffic on final approach for runway 02 “is almost head-on, so the controller has no perspective of the separation between two consecutive aircraft on approach” with the only way to discern distance at night being the brightness of the aircraft landing lights which only serves to distinguish very long distances from very short distances.
- Visibility of the other runway from the aircraft flight deck of aircraft was reviewed. It was concluded that the chances of an aircraft accelerating for takeoff on runway 06R and an aircraft on final approach to runway 22 detecting each other was “very low” with the departing aircraft least likely to be able to see the approaching one since it would be almost directly to the right and sighting it "would require a 90º head turn to the right”.
- The A320 flight crew were familiar with the use of late landing clearances even as late as when at 50-80 feet agl and on receiving warning of one were prompted to look ahead for this traffic on their runway and heard it report clearing. They reported first seeing the 737 after crossing the coastline when at 200-300 feet agl and having “assessed that it would take some time to get airborne, they had decided to continue with the approach as climbing at that point would be worse due to the change of aircraft configuration and the possible descent and change of attitude that commencing a go around would entail”. They reported having been surprised when, after crossing runway 06R, the controller instructed them to go around. They said that they “did not hear the (737) takeoff clearance” and “were not expecting traffic taking off on 06R”.
- The description of the event by both 737 pilots “was consistent with the sequence of events obtained from radar traces and ATC communications”. They were informed that there was traffic on approach to runway 02 at 4nm and “deemed that this was sufficient to be able to depart”. They remarked that “visually, it was impossible to assess whether the approaching aircraft was further away than or closer than 4 nm”. Before entering the runway, they reported having “looked towards the 02 approach path (and) saw that there were a lot of lights on the approach”. Once on the runway, they noted that the view of any approaching aircraft would have been “highly oblique, at more than 90º”. They recalled that shortly after the 80 knot call “at about 90-100 knots they had seen an aircraft they were not expecting pass in front of them”. Their VR was 140 knots and they did not consider rejecting the takeoff because the aircraft had already crossed over and “they judged that their takeoff had not been compromised”.
- It was considered that the A320 crew had been understandably focused on the aircraft ahead since that was (correctly) assumed to be the reason they had been told to accept late landing clearance. They were unaware that the actual reason was the 737 departing runway 06R.
Conclusions (in summary)
- The A-SMGCS Level 2 system detected the conflict correctly and issued a violation alert.
- The controller's reaction to this alert was delayed.
- The A-SMGCS system frequently produced false alarms.
- The approaching aircraft detected the conflict shortly before the crossing and decided to continue with the approach.
- The aircraft on takeoff did not detect the conflict.
- The conflict was a “Runway Safety Event” rather than a ”Runway Incursion”
Editor’s Note: Although the A320 overflew runway 06R at a height of 59 feet, the 737 tail height is just over 41 feet so had the 737 been directly below the A320, the vertical separation would have been just under 18 feet. And had the A320 been overhead runway 06R when it reached its minimum height then the vertical separation would have been just over 3 feet.
The Probable Cause of the conflict was determined as “the issue of a clearance to take off from runway 06R with traffic on approach to runway 02 at less than the (minimum) 4 nm distance established for the prevailing runway configuration”.
Four Safety Recommendations were made based on the Findings of the Investigation as follows:
- that ENAIRE, as the ATC service provider for the Barcelona control tower, assess the possibility of implementing in the automated ATC system (SACTA) an automated change of arrival runway on the General Information Panel each time a change of arrival runway is made in the Runway Use menu. [REC 51/23]
- that ENAIRE, as the ATC service provider for the Barcelona control tower, increase the robustness of the current information systems with regard to discrepancies between the runway selected in the Runway Use menu and the runway selected on the General Information Panel. [REC 52/23]
- that ENAIRE, as the ATC service provider for the Barcelona control tower, draft a control position checklist to facilitate the detection of any oversights during configuration changes. This checklist should include checking the arrivals runway on the General Information Panel after a change of configuration, particularly for the TWR controller responsible for arriving traffic. [REC 53/23]
- that ENAIRE, as the ATC service provider for the Barcelona control tower, review and disseminate information on:
- When to use the term “expect late landing clearance” and the point to which a clearance can be delayed.
- The effect that the use of this expression had on the approaching aircraft's crew, in causing them to focus almost exclusively on their runway. [REC 54/23]
The Final Report of the Investigation was approved on 24 April 2024 and subsequently released online simultaneously in both the definitive Spanish version and in English translation.