Easyjet Europe A320 and Norwegian B738 at Edinburgh on Aug 13th 2018, loss of separation on runway

Last Update: May 30, 2019 / 17:16:53 GMT/Zulu time

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Photo of Easyjet Europe OE-IVC, Airbus A320 — Easyjet Europe OE-IVC, Airbus A320 (Photo credit: airlines470 / Flickr / License: CC by-sa)

Incident Facts

Date of incident
Aug 13, 2018

Classification
Report

Airline
Easyjet Europe

Flight number
U2-14

Departure
Edinburgh, United Kingdom

Destination
London Luton, United Kingdom

Aircraft Registration
OE-IVC

Aircraft Type
Airbus A320

ICAO Type Designator
A320

An Easyjet Europe Airbus A320-200, registration OE-IVC performing flight U2-14 from Edinburgh,SC to London Luton,EN (UK) with 180 passengers and 6 crew, was accelerating for takeoff from Edinburgh's runway 06.

An Norwegian Air International Boeing 737-800, registration EI-FJW performing flight D8-1601 from Newburgh,NY (USA) to Edinbugh,SC (UK) with 159 passengers and 7 crew, was on final approach to Edinburgh's runway 06 advised to expect a late landing clearance. The aircraft continued for the approach until the flare, when the crew received landing clearance, touched down and rolled out.

The AAIB reported that by the time the landing B738 flew over the runway surface the departing A320 was still in the takeoff roll. The distance between the two aircraft reduced to 875 meters/2870 feet horizontal. The A320 became airborne 2 seconds prior to the B738 touching down.

The AAIB released their final report concluding the probable causes of the serious incident were:

A succession of short delays to the departure of OE-IVC and the higher than normal speed approach of EI-FJW led to the rapid closure of the gap between EI-FJW and OE-IVC. The loss of spacing went unnoticed by both the trainee controller and the On-the-Job-Training-Instructor (OJTI) until EI-FJW came out of cloud which was just before the crew prompted them by calling at 0.5 nm. At this point the OJTI made the decision that it was safer to land EI-FJW than risk having two aircraft that he could not separate visually close to each other in cloud above the airport.

The crew of OE-IVC were completely unaware of the developing situation as they could not see EI-FJW nor had the trainee controller instructed them either to be ‘ready immediate’ or cleared them for an ‘immediate takeoff’.

The AAIB reported Edinburgh tower was staffed by a trainee controller and an OJTI (On-the-Job-Training-Instructor).

The A320 had taxied to runway 06 via taxiway A and was holding short of A1. The B738 was at about 6nm from the threshold when tower cleared the A320 to line up runway 06. However, the trainee controller did not turn off the stop bar lights. Another aircraft called ready for departure and the controller talked to them for 9 seconds. Immediately after this transmission the captain of the A320 transmitted "stop bars!", the controller turned off the stop bar lights. The A320 began to taxi into position about 29 seconds after the stop bar lights extinguished.

35 seconds after the A320 began to taxi into position tower cleared the A320 for takeoff from runway 06, the B738 was about 3nm from touchdown.

The A320 began their takeoff run about 40 seconds after being cleared for takeoff, the B738 was just over 0.5nm from touchdown at that point. Reaching 0.5nm from touchdown the B738 called tower reminding tower they had not yet been cleared to land.

The OJTI took over from the trainee controller, decided that it was safer to have the B738 continue the landing instead of having two aircraft over the airport in clouds and not being able to separate from each other visually. The B738 continued, crossed the runway threshold and wsa already in the landing flare when the OJTI issued landing clearance just as the A320 became airborne. 2 seconds later the B738 touched down, the horizontal distance between the two aircraft was 875 meters at that time, the A320 had climbed to 60 feet AGL by that time.

The AAIB reported that the B738 was flown by 3 captains: a captain under supervision was occupying the left hand seat, a training captain occupied the right hand seat and was commander of the flight, and a training captain supervising the captain in the left hand seat occupied the observer's seat.

The AAIB analysed:

At 0945:55 hrs, the preceding aircraft landed at EDI. At this point EI-FJW was 6 nm from touchdown, which was exactly the spacing required in the EDI MATS Part 2 for gap mode.

The trainee controller then preceded to give OE-IVC line up clearance as had been planned for the gap before EI-FJW landed. Due to a combination of factors, the gap rapidly closed and the departing aircraft was at only 60 ft aal when the landing aircraft touched down.

Factors leading to the gap closure

Stop Bar

The airfield was in safeguarding due to the meteorological conditions and, therefore, the Stop Bars were in use. The trainee controller did not have much experience of working in conditions similar to those of the day of the incident and had little experience of using the Stop Bars. The Stop Bar was not turned off expeditiously and, as a result, OE-IVC could not move from the holding point to line up. There are two possible explanations; the trainee controller may have forgotten to do it or may not have activated the Stop Bar controls correctly. Turning off the Stop Bar requires a controller to move a cursor using a mouse and click within a very small box, before moving the cursor to the beginning of the active runway and clicking again. During this process, the cursor may have been mispositioned or the selection may have been performed in the wrong order, leading to the Stop Bar remaining illuminated.

Having been cleared to line up but with the Stop Bar still illuminated, it was natural for the crew of the departing aircraft to then question the illumination of the Stop Bar with the controller. However, before the crew of OE-IVC could do this, another aircraft on the same frequency egan a transmission. As a result, there was a 16 second delay between OE‑IVC being cleared to line up on Runway 06 and the crew asking the controller to turn off the Stop Bar so they could proceed onto the runway. This delay caused a significant part of the gap closure.

Speed of landing aircraft on approach

EI-FJW had been instructed by EDI approach to maintain a speed of at least 160 KIAS on the approach until 4 nm to assist with the spacing between it and the following aircraft. It would have been more usual for an aircraft on the approach to be instructed to maintain a speed of exactly 160 KIAS until 4 nm from touchdown, so the instruction given to EI-FJW permitted the aircraft to be flown at a higher speed than was normally expected. The crew complied with the instructions and were at 181 kt ground speed at 6 nm when the preceding aircraft touched down on the runway. EI-FJW complied with all the operator’s requirements for a stable approach, having begun to slow after they passed 6 nm from touchdown. The higher than normal speed of EI-FJW on the approach may have caught the trainee controller by surprise.

Any speed control given to an approaching aircraft by the radar controller was displayed on the strip information, and the groundspeed was displayed on the radar picture display at the tower controller’s station. However, the trainee controller was more familiar with being able to see the aircraft on the approach and to judge the gap visually rather than relying on the screens provided. With the weather conditions, the trainee controller was unable to see the aircraft until it was inside 2 nm from touchdown. The higher speed of the approaching aircraft combined with the less familiar need to refer to the radar display meant that the closure of the gap went unnoticed until the late stages of the approach.

The OJTI, seated or standing behind the trainee controller could not see the screens in detail without making a deliberate attempt to move his position, so the developing situation may also have not been obvious to him.

Time taken for the departing aircraft to take off

The crew of OE-IVC were unaware of the closing gap. They had not been instructed to expedite their line-up, nor had they been cleared for an immediate takeoff. Had either of the tower controllers issued these instructions it is likely that the training captain would have taken control of the aircraft and conducted the takeoff. The training captain estimated that this could have saved 10-15 seconds.

Reaction to the closing gap

EI-FJW

The crew of EI-FJW were familiar with the much busier air traffic environment of LGW, where the aircraft spacing is optimised to allow a large number of movements from a single runway. They were not concerned about the closing gap, as they did not consider it unusual. As the aircraft approached 0.5 nm from touchdown, they could clearly see the other aircraft was still on the runway. PM called the tower controller and was told to expect a late landing clearance. This confirmed in the minds of the crew that the controllers were fully aware of the position of both aircraft.

The crew in EI-FJW consisted of three captains, which, for the reasons given earlier, could make the dynamics of decision making challenging especially when considering that the captain who was PM in the left seat was being assessed before completing his training.

There may have been reluctance from all three pilots to voice their concerns for fear of jeopardising the assessment.

The aircraft commander reported he was tired due to the overnight flight and his previous roster that included several transatlantic flights. He had had as much sleep as could be expected given his roster pattern and his flying performance was unlikely to be affected by fatigue. However, his feeling of tiredness may have made him hesitant to go around because this would extend the flight time.

The phenomenon of plan continuation bias may also have added to the crew’s reluctance to go around even when they had not received a landing clearance at such a late stage.

Plan continuation bias is an ‘unconscious cognitive bias to continue [the] original plan in spite of changing conditions’. The bias can cause people to discount cues which indicate the situation requires a different course of action and has a stronger effect on behaviour the closer someone is to the completion of their plan; for example, the closer someone is to landing at the planned destination.

Overall, the above factors came together to contribute to the crew of EI-FJW not making a decision to discontinue the approach and go around.

OE-IVC

The crew of the departing aircraft were unaware of the developing situation and so could not react. The absence of any indication from the tower to the contrary resulted in the aircraft departing as planned. Even after takeoff, they were completely unaware of the situation that had developed and the closeness of EI-FJW behind them.

Controllers

The trainee controller was still relying on techniques more suited for use in better weather conditions. The trainee controller was using a rule-based strategy which checked the gap was sufficient as the preceding aircraft touched down and was not effectively monitoring the aircraft speeds or size of the gap as the situation progressed. All this meant that the trainee controller did not become aware of the gap closure until late and so then had little time to react.

As the crew of EI-FJW called at 0.5 nm, the trainee controller responded by instructing EI‑FJW to continue the approach. This call also coincided with the RIMCAS Stage 2 visual and audible alert which would have continued in the background until cancelled. Both the 0.5 nm call and the RIMCAS Stage 2 alert may have been unfamiliar to the trainee controller. Whilst the trainee controller would have been familiar with the instructions in EDI MATS Part 2 stating that a RIMCAS Stage 2 alert requires the issue of a go-around unless it is ‘positively known that there is no runway infringement’, the trainee controller did not have the capacity or experience to immediately make that decision.

The trainee controller had little or no experience of instructing a go-around. This inexperience, together with the short time period available to act after becoming fully aware of what was happening resulted in an inability to recover the situation. The lack of experience probably also caused a reluctance to intervene in such a serious situation immediately without confirmation from the OJTI that it was the correct thing to do.

The OJTI was monitoring the trainee controller but had missed the developing situation. He became aware of the seriousness of the situation when EI-FJW came out of cloud a few seconds before the RIMCAS Stage 2 alert began to sound. He was startled by the suddenness of the situation and this caused a further delay in his reaction. His immediate concern was for the separation of the two aircraft. He could see both aircraft out the window and although they were close he was not concerned about them closing together.

He considered that it was too late to stop OE-IVC taking off as he considered its speed was above 80 kt because it had passed the glide path aerials as specified in EDI MATS Part 2. His options were therefore to either instruct EI-FJW to conduct a go-around or allow it to land. His biggest concern was that if he instructed the go-around, he would have two aircraft, which he could see were close, disappear into cloud where he could not visually separate them. He made the decision to allow EI-FJW to land, which he did by giving them landing clearance. He considered that the decision was the safest at that point.

An earlier intervention could have enabled EI-FJW to go around whilst keeping OE-IVC on the ground, preventing the risk of two aircraft in cloud without minimum separation.

Had EI-FJW gone around from the approach, both aircraft would have been airborne with limited lateral separation. Given the TCAS inhibits, neither would have received an RA until reaching 1,000 ft radio altitude (737) or 1,100 ft radio altitude (A320). Whether the aircraft would have received an RA after this point would have depended on the actions of the controller to separate the aircraft, and their relative speeds and climb rates. It is not possible to model the flight paths of the aircraft accurately enough to be able to fully understand whether the TCAS RA would have been activated.

Being an OJTI can be a challenging position which requires experience and sound judgement to decide when and how to intervene with a trainee. The OJTI was relatively inexperienced in the role which would have made intervention decisions more challenging. As a trainee controller progresses through the training programme, OJTIs are encouraged to intervene less and less to allow the trainee controller to develop the skills and confidence required to qualify. With the trainee controller a considerable way through the second of three parts of the training, the OJTI would have been expecting the trainee controller to perform with little or no support from him. He had also had two sessions in the days before the incident during which the trainee controller had performed well. These factors and the difficulty of reading the screens could explain why the OJTI was not monitoring the situation closely once the initial gap had been checked and thus it increased the surprise21 factor when the seriousness of the situation became clear to him.

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