Norwegian International B738 at Alicante on Jun 7th 2018, rejected takeoff due to operational error (vehicles on runway)
Last Update: July 17, 2019 / 17:22:43 GMT/Zulu time
The aircraft returned to the holding point runway 10 and departed about 6 minutes later.
Spain's CIAIAC reported Alicante's tower had cleared two vehicles to enter runway 10 at the end for a runway inspection. About 4 minutes later the controller cleared the Boeing for takeoff. The vehicle drivers, who were listening to the tower frequency, reported immediately they were still on the runway, which prompted the controller to instruct the Boeing to stop. The crew rejected takeoff and vacated via a taxiway. The occurrence is being investigated by the CIAIAC.
On Jul 17th 2019 the CIAIAC released their final report reporting the probable cause of the incident was:
The incident occurred because aircraft IBK2WH was issued an incorrect takeoff clearance by the tower when the runway was occupied by two runway and apron service vehicles that had previously been cleared to enter the runway.
The following contributed to the incident:
- The possible excessive workload for a student controller.
- The single-position configuration in the tower.
- The lack of effective supervision by the instructor at the time of the incident.
- The use of Spanish to communicate with the SPP vehicles, which prevented the crew of the aircraft from understanding their content.
The CIAIAC summarized the event:
At the time of the incident, with one control position staffed in the control tower, there was a student controller in training and an instructor.
Four minutes earlier, at 16:26, the control tower had cleared two runway and apron service (SPP in Spanish) vehicles to check the runway. These vehicles were on the runway at the time of the takeoff. The takeoff clearance given to the aircraft was heard by the SPP vehicles, which immediately cleared the runway and informed the tower of the situation. The controller instructed the aircraft to reject its takeoff. The vehicles exited the runway without further incident. The aircraft stopped its takeoff run and also exited the runway without further incident.
The investigation has determined that the distance between the aircraft and the two vehicles was in excess of 1000 m throughout the event.
The CIAIAC annotated that at the time of the takeoff clearance the frequency had been busy for 70.1% of time during which the controller handled:
- Coordination with an SPP car to reposition EZY34RE.
- 1 taxi clearance for EZY34RE.
- 1 clearance issued to last departing traffic (IBK5302), which was still outstanding.
- 1 proactive clearance issued proactively (that is, with no call made by the crew) to a departing aircraft (EZY45DR).
- 1 clearance request for a new departing aircraft (RYR761Y9), which he tells to stand by.
- Information to AFL2523 that its CTOT is 16:43.
- 1 line up and wait clearance for IBK5358.
- 1 takeoff clearance for IBK2WH
Following the rejected takeoff the aircraft vacated the runway via taxiway C2 about 1600 meters/5200 feet down the runway. The crew acknowledged the reject takeoff instruction as the aircraft was accelerating through 80 knots over ground, the maximum speed reached was 88 knots over ground.
The CIAIAC analysed:
The interaction between the SPP vehicles and ATC, as just another operator, was correct. The communication procedure employed with ATC was appropriate. They communicated their position at all times, reported their intentions and acknowledged the instructions issued by ATC. In fact, when they were unable to acknowledge their instruction to enter the runway at the 28 threshold, they stayed where they were. Their positions during the entire incident were known to ATC and were correctly annotated by the controller on the strip.
The practice by both drivers when picking up objects from the runway of driving as close as possible so as not to have to get out of and move away from the car, allowed the drivers to monitor the tower frequency constantly. When the aircraft was cleared to take off, PAPA6 was picking up some debris, but this did not prevent the driver from monitoring the tower frequency. The active listening by the drivers at all times while driving the SPP vehicles allowed them to identify the conflict and provided a barrier that kept the incident from becoming worse. Considering the speed and acceleration of an aircraft of these characteristics, which is airborne in 37 s (as the second takeoff showed), a delay in identifying the conflict may not have allowed the vehicles to vacate the runway on time.
Both drivers, the COAM and the TOAM, immediately detected the conflict. Their reaction was immediate and similar: to vacate the runway as quickly as possible. The frequency was busy, which prevented them from communicating with the TWR until 25 s after the conflict began, but by then they had already taken the initiative and vacated the runway. The reaction of the SPP vehicles was fast and appropriate.
Lastly, the use of English to give the takeoff instruction to the aircraft did not prevent the TOAM and COAM from understanding it. Thanks to this, they identified the conflict situation they were in and took measures that helped to mitigate the consequences of the incident. All communications between the tower and the SPP vehicles were held in Spanish, which kept the crew of the aircraft from understanding the instruction clearing the SPP vehicles to enter the runway. If this instruction had been given in English, it may have made it more likely for the aircraft crew to detect the conflict, and not just the SPP vehicle drivers.
From the standpoint of the aircraft and its actions during the incident, the main conclusion is that it did not contribute to the incident. As with the SPP vehicles, the communications held with the TWR were complete and correct, and each of the aircraft’s position in the airport was known by the TWR. The movements made by the aircraft were authorized by the controller, and at no point was the aircraft in an unauthorized position.
There was no visual contact between the crew and the SPP vehicles, as confirmed by both the crew and the drivers. This was due not only to the gradient of the runway, but primarily to the distance separating them (in excess of 1000 m at all times).
With respect to the controller the CIAIAC analysed:
Since the runway is completely visible from the controller’s position in single-position operations, that makes it possible to identify the vehicles on the runway, and since visibility on the day of the incident was ideal, and assuming the information on the strip board was true, there are two possibilities:
- The takeoff clearance was given without looking at the strip board (that is, looking outside), or
- The takeoff clearance was given while looking at the strip board (that is, looking inside).
The first option would mean that the student did not visually scan the entirety of the runway (from one threshold to another), since in that case he would have seen the SPP vehicles. The second option would mean that he did not assimilate the information he was seeing on the strip board. The ATC communications showed that the takeoff clearance was issued as the aircraft was entering the runway, before lining up with the centerline. That clearance, at that moment, implies that the controller must have been looking at the aircraft. It thus seems likely that the clearance was given with the controller looking at the runway, but only focusing on the threshold.
The ATC communication in the 20 minutes prior to the event showed high use of the frequency. The student controller’s actions were correct (use of phraseology, acknowledgments, situational awareness and proactivity). His English level was very high, and this is not thought to have been a factor that influenced the incident.
The controller’s faster speaking speed as time went by was obvious in his communications, no doubt a result of the increased activity at the airport, and to offset the long time needed for clearance delivery (11 to 17 s) and the pushback and start up clearances (7 and 11 s) he had to issue, in comparison to the other clearances (taxi, line up and wait, takeoff and transfer to APP, lasting 3 to 6 s).
The number of aircraft handled during this 20-minute period was 10 departing and 1 arriving aircraft, along with other activities (CECOA and SPP vehicles). The listing of tasks (section 1.9) carried out during the time the controller was on watch indicates that the activity on the frequency was high. The workload increased above what was expected when an aircraft requested to reposition, which doubled the number of communications and coordination required. The increased delay in issuing clearances (from being issued immediately at the start of the shift from being delayed 2-3 minutes) is indicative of the controller’s increasing workload.
Potential evidence of the increase in workload, in addition to the high use of the frequency, the faster speaking speed and the need to delay clearances, is the fact that in the takeoff clearance issued to IBK5358, the controller forgot to include wind data.
To the above we must add the fact that the controller on the frequency was a controller in training, whose cognitive effort is higher than that required of a more experienced person. The student was also a perfectionist, who was in training, who had made two mistakes that the instructor had pointed out to him, one of which was the focus of the training phase he was in. The focus that the student himself mentioned on achieving the proper takeoff sequence, while ignoring the strip board and the lack of visual monitoring, could be the result not only of a lack of experience, but of the student’s abilities being undermined by the increase in workload.
In short, there are indications that the student could have been subjected to a workload during the incident that was too high for him, which affected his ability to focus on and execute tasks that he normally carried out very meticulously.
However, based on the service provider’s own criteria, the number of positions that should have been staffed for this expected number of movements should have been two, since it exceeded the stated capacity by 3 movements/hour and the maximum capacity by 1 movement/hour.32 These values were taken into account by the instructor when setting up the unit, and for the first ten minutes, he in fact staffed two positions. The decision to close one was due, according to the instructor’s statement, to the subsequent reduction in traffic and to the fact that keeping two positions open for the entire hour would not benefit the student, because the workload would be too low for him.
The reality of the incident is that the amount of work in a single-position configuration was too much for the student, and while the decision may have been correct, it may have required more active oversight from the instructor.
With respect to the controller's instructor the CIAIAC analysed:
Because he was a controller in training, there was an instructor in the control room to help with and supervise the controller’s actions. In this incident, the instructor’s oversight was evident in two observations he made to the student (when the SPP vehicles did not enter the runway the first time, and when he sequenced the three departing aircraft incorrectly before the incident), and when he corrected the assistant’s mistake when placing a strip on the bay.
As his statement showed, he was tracking the sequence of events and was aware of the situation with the vehicles and aircraft, so he knew immediately what had happened when he heard PAPA6 report the event. The immediate instruction he gave the student to cancel the takeoff shows that he was perfectly cognizant of the traffic situation at the airport.
However, at the last second, he did not exercise this oversight, and the incident occurred. Based on the information gathered during the investigation, this distraction was due to:
- Excess confidence in the abilities of the student controller.
- Lack of experience as an instructor, since it was his second day acting in that capacity.
- Excessive attention to the assistant, to whom he was giving explanations at the time of the incident.
- Lack of experience of the assistant, who was on his first day on the job.
This article is published under license from Avherald.com. © of text by Avherald.com.
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