Description

On 3 February 2019, an Airbus A320neo (SE-DOY) being operated by SAS on an international passenger flight from Copenhagen to Amsterdam as SK 553 failed to follow its post-landing taxi clearance and passed within a few metres of an Airbus 320 (G-EZWY) being operated by Easyjet U2 8885 on an international passenger flight from London Gatwick to Amsterdam. The crew of the Easyjet aircraft saw the impending collision risk and performed an emergency stop just in time to prevent impact. The conflict occurred at night in good ground visibility but the other aircraft crew did not notice the conflict and continued past the stopped aircraft at speed. 

Investigation

The Dutch Safety Board was informed of the event the following day and commenced a Serious Incident Investigation using recorded ATC radar and GND frequency transcripts to corroborate (or otherwise) the statements of those involved.

It was noted that all four pilots involved were experienced A320 pilots and familiar with the particular complexity of ground manoeuvring at Amsterdam as operated. The Easyjet A320 Captain had a total of “around 9,500 hours” flying experience and their First Officer had a total of “around 3,400 hours” flying experience. The SAS A320 Captain had a total of “around 15,500 hours” flying experience and their First Officer had a total of “around 11,500 hours” flying experience. The Captains of both aircraft were acting as PF during their respective taxi in.

What Happened

Runways 18C and 18R were in simultaneous use for landings. The Easyjet A320 had landed on runway 18R and was initially cleared to taxi via taxiway Z and then to cross taxiway Z2 and continue north on taxiway ‘A’ to its allocated gate H1 (see the illustration below). Half a minute later, the GND controller added “Scandinavian on the left at the end of Zulu waiting for you” which was correctly read back. The Easyjet crew stated that they had clearly seen the other A320 taxiing south on taxiway ‘B’ and estimated its speed as “around 20 knots”. When their aircraft turned left and began heading north, the Captain stated that he still had the other A320 in sight. 

As they approached the intersection of taxiway ‘Q’ with taxiway ‘A’ and ‘Z’, the Easyjet Captain reported seeing the other aircraft approaching them from the left “at an angle of about 45 degrees”. Then, between taxiways A26 and A27, as the two aircraft continued to close, the Captain noted that the SAS A320 was not slowing down so, as a precaution, he reduced speed to 10 - 15 knots and when it became obvious that the other A320 was not going to stop as advised by GND, he made an emergency stop. He stated that once stopped, he had seen the right wing tip of the other aircraft passing the nose of their aircraft from left to right at an estimated distance between the wing and the nose of 3-4 metres. It was clear that if the Easyjet Captain had not stopped then a collision was certain to have occurred. Immediately after the near miss, the Captain expressed his concern and surprise to both the SAS crew and the GND controller and the SAS crew apologised for their error. The Easyjet A320 then continued north on taxiway ‘A’ as previously cleared. 

The ground tracks of the SAS AA320 (red) and the Easyjet A320 (blue) up to the conflict point. [Reproduced from the Official Report]

The SAS A320 had landed on runway 18C and been cleared to taxi via taxiway B and taxiway Q for gate C10 but with the condition that “when turning at Quebec give way to the Easy right side from Zulu”. This condition was only partially confirmed by the First Officer with “give way to the Easy, Scandinavian 87L”. The Captain claimed that “the controller did not indicate the position of the aircraft or from which direction it would come”. 

The GND controller involved noted that as the outlines of aircraft he could see from the VCR were less visible at night than they would be at daylight, he had “additionally used ground radar to monitor the movement of aircraft” and he recalled that his frequency had been quite busy. He stated that in issuing taxi-in clearances to both aircraft, he had foreseen that they may well arrive at the same intersection at a similar time which was why he had made the clearance to the SAS 320 conditional. Both instructions had been given around 1½ minutes prior to the potential intersection crossing conflict. He stated being aware that the SAS aircraft “did not mention the place where they had to give way and the direction where the aircraft would come from” but had not challenged it. He had no further communication with either aircraft until after the conflict and added that when he had “occasionally monitored the movement of both aircraft" on radar both aircraft were continuing as instructed and he had "expected both aircraft to comply with their instructions" and had been unaware that they had almost collided until he heard communications between the two flight crews immediately after the occurrence. 

Discussion Points 

It was observed that: 

• the First Officers of both the aircraft involved were ‘head down’ during the period leading up to the near collision, both reportedly reviewing the electronic airport chart in relation to the taxi in clearance they had been given. This meant that the respective Captains lookouts had not been duplicated and their compliance with the issued clearance was not being monitored.
• the fact that the SAS Captain did not notice the conflicting Easyjet A320 despite being told to expect to see it and where this would be was suggested by him to be a result of “the darkness in combination with a large amount of background lighting (including but not limited to) the motorway lighting in the background (which) can make it difficult to detect the relatively modest lights from other taxiing aircraft, especially when these are still far away”.
• all taxiways in use at Amsterdam have their green centreline continuously illuminated “contrary to some other airports” where only taxiway routes to be followed in accordance with a specific clearance have lit centrelines.
• In a situation where the GND controller is unable to monitor compliance with clearances issued, a challenge in the event of an incomplete clearance readback is essential and “more active control and provision of instructions when both aircraft are approaching each other is essential”. 

The Cause of the Serious Incident was recorded as "the crew of the aircraft that had to give priority not noticing the other aircraft in time". 

Six Contributory Factors were also identified: 

• The early instruction of the ground controller and the lack of later, additional instructions.
• The crew either did not hear or did not recall where to expect the other aircraft neither did they challenge air traffic control.
• The ground controller did not challenge the crew when they gave an incomplete read back.
• The darkness and background lighting in combination with the complexity of the location at Amsterdam Airport where the incident occurred and other tasks of the flight crew.
• The darkness and the distance between the control tower and both aircraft.
• The limitations of visual observation during darkness in combination with the properties of the ground radar system.

It was also concluded that: 

• in circumstances such as those which prevailed on this case "it is preferable (for ATC) to repeat stop instructions and continue to stay in touch with crews, until they have a clear picture of the situation and the possibility of making mistakes is reduced".
• the taxiway intersection where the conflict occurred was not designated as a hotspot, but several taxiways converge there.
• despite the presence of designation signage, flight crews must be extra alert to distinguish the different intersections, especially in darkness due to the extensive background lighting and the illumination of multiple taxiways.
• the possibilities for visual monitoring during darkness by a GND controller in combination with the restricted capabilities of the available ground radar, are not optimal. It is therefore important for GND controllers to verify that clearances have been properly heard and fully and correctly read back.
• it is preferable for GND to repeat stop instructions and regularly to monitor the aircraft, until they have a clear picture of the situation thereby reducing the possibility of errors. For flight crews it is important to verify an instruction in the case it creates ambiguity.

The Final Report of the Investigation was published on 22 September 2021.  

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