Alert
On Saturday, January 18 2020, 16 landings took place on runway 18C /36C (Zwanenburgbaan), although this runway had not yet been formally made available to LVNL at that time. These landings took place over a period of 25 minutes. All parties involved were aware of the use of runway 18C /36C (Zwanenburgbaan). The runway had been inspected, and the runway lighting with the corresponding stopbars that protect against unauthorized entry onto the runway had been switched on. This ensured that there was no risk of collision.
LVNL reported the occurrence to the Dutch Safety Board (Onderzoeksraad voor Veiligheid) and is also conducting its own investigation into this occurrence.
Description of occurrence
At Schiphol Airport, runway 36L (Polderbaan) and runway 24 (Kaagbaan) were in use for outbound traffic and runway 27 (Buitenveldertbaan) was in use for inbound traffic. During an outbound peak, Schiphol uses two take-off runways and one landing runway. In addition to runway 27 (Buitenveldertbaan), which is already in use for outbound flights, air traffic control had also scheduled use of runway 36C (Zwanenburgbaan) to handle inbound traffic for the upcoming inbound peak, partly on the basis of expected wind direction. The plan was to reduce outbound flights from runway 24 (Kaagbaan).
During an inbound peak, two runways are used for landing and one runway is used for take-off. The runway combination during the anticipated inbound peak was supposed to be: take-off from Polderbaan and land on runway Buitenveldertbaan and Zwanenburgbaan.
Inspection of runway 36C (Zwanenburgbaan)
More than half an hour before the planned use of runway 36C (Zwanenburgbaan), it was inspected by the airport at the request of the air traffic control tower. The formal request to the airport for availability of the runway was not communicated directly.
Precautionary landing on runway 27 (Buitenveldertbaan)
Fifteen minutes before the planned use of runway 36C (Zwanenburgbaan), it became known that an inbound aircraft would make a scheduled precautionary landing on runway 27 (Buitenveldertbaan). Because it had been indicated that this aircraft would block the runway after landing, inbound traffic that was supposed to land on runway 27 (Buitenveldertbaan) was diverted to runway 36R (Aalsmeerbaan).
Inspection and availability of runway 36R (Aalsmeerbaan)
Before runway 36R (Aalsmeerbaan) was put into use, it was inspected by the airport at the request of LVNL. After the inspection of the runway had taken place, the air traffic control tower requests the airport by telephone (as prescribed by the procedure) to make runway 36R (Aalsmeerbaan) formally available to LVNL. The runway status panel then showed a visual indication (runway is illuminated yellow on the panel) that runway 36R (Aalsmeerbaan) had been formally made available to LVNL by the airport.
Start of inbound peak; runway lighting switched on for runway 36C (Zwanenburgbaan)
After the last take-offs had taken place from runway 24/06 (Kaagbaan), the inbound peak started. The first aircraft for landing on runway 36C (Zwanenburgbaan) reported in. The runway lighting on runway 36C (Zwanenburgbaan) and associated stop bars, which protect against unauthorised runway access, had been switched on by tower traffic control.
Request to make runway 36C (Zwanenburgbaan) formally available
By that point, sixteen landings had taken place on runway 36C (Zwanenburgbaan). Tower control observed that the runway in question had not yet been formally made available to LVNL by the airport. This was visible because runway 36C (Zwanenburgbaan) was not illuminated yellow on the runway status panel. Once this had been established, the tower immediately contacted the airport to make runway 36C (Zwanenburgbaan) formally available.
Go-around
It took some time to make runway 36C (Zwanenburgbaan) formally available. Therefore, the next inbound aircraft at 1.1 nautical miles (two kilometres) from runway 36C (Zwanenburgbaan) was instructed by tower control to make a go-around. This was to prevent another landing on the runway that had not yet been made available. The aircraft executed this standard procedure. After instruction, the aircraft first descended to an altitude of approximately 200 feet (60 meters) above the runway and then climbed to the standard altitude for a go-around.
Runway 36C (Zwanenburgbaan) formally available
Shortly after this, runway 36C (Zwanenburgbaan) appeared on the runway status panel ‘illuminated yellow'. After that, inbound aircraft continued landing on runway 36C (Zwanenburgbaan). The aircraft that made the go-around also landed safely on runway 36C (Zwanenburgbaan) a little later.
The sixteen landings on a formally unavailable runway were all registered as runway incursions (category D, no direct safety effect).
Results of the investigation
No formal request to airport
In accordance with the procedures, the airport was informed by LVNL prior to the planned use of runway 36C (Zwanenburgbaan) as a landing runway. As part of this, the runway was then inspected by the bird controller.
After an inspection, LVNL must formally ask the airport to make the runway available. This did not happen, because runway 36C (Zwanenburgbaan) was being used to allow aircraft to cross, in this case towards runway 18R/36L (Polderbaan) which was being used for outbound aircraft. As a result of the request for availability of runway 36C (Zwanenburgbaan), the stop bars that secure the crossing to and from runway 36L (Polderbaan) were switched on. Switching these stop bars on and off for every aircraft that wants to cross means a great deal of additional coordination for the air traffic control tower; this requires considerable attention. Therefore, the decision was made not to immediately request the availability of the runway, since crossings were still taking place; the plan was to do this at the time of the last agreed runway crossing of runway 36C (Zwanenburgbaan).
The runway lighting and the stop bars of runway 36C (Zwanenburgbaan) were switched on just before the last runway crossings. The final step of the administrative task of formally requesting the availability of the runway (request availability by phone) did not take place due to the intense level of dynamic activity at the tower at that time. This was mainly due to the following activities happening simultaneously within a short period of time: the handling of the precautionary landing on runway 27 (Buitenveldertbaan), escort by emergency services for this landing, the use of runway 36R (Aalsmeerbaan) and the corresponding restructuring of the traffic flows because it was no longer possible to use runway 27 (Buitenveldertbaan), the last few crossing aircraft at runway 36C (Zwanenburgbaan), and extra bird chasing on runway 24 (Kaagbaan). The focus of the air traffic control tower was on these activities; as a result, the phone request to make the runway available was not made.
No risk of collision
The potential risk of landing on a runway that has not been made available is that a conflict could arise between an inbound aircraft and another aircraft or vehicle on the same runway. The parties involved were aware of the planned use of runway 36C (Zwanenburgbaan), and the runway lighting and associated stop bars were on. At all times, regardless of the status of the runway, permission from tower control is required for an aircraft or vehicle to enter a runway and for an aircraft to land.
At the moment that it became clear that the runway had not been made available, the decision was made to have the next aircraft execute a go-around instead of making a landing on an unavailable runway. This was to prevent an additional runway incursion.
Runway 36C (Zwanenburgbaan) was not yet available in administrative terms; however, due to the aforementioned factors, it would have been impossible for there to be any conflicting traffic at the time of the landings on that runway. That is why there was no risk of collision.
Follow-up to the investigation
The main cause of the incident was the fact that LVNL air traffic control did not request that Amsterdam Airport Schiphol formally made the Zwanenburgbaan available.
New safety net prevents repetition
In order to prevent precisely these types of situations, LVNL has been working on additional system support for some time now. Developing such support became possible after the implementation of Electronic Flight Strips (EFS) in the tower in 2019. During the night of 16 to 17 March 2020, this new safety net was successfully implemented in the EFS system at the Schiphol towers. The new function gives an additional warning that the runway is unavailable and blocks the electronic flight strips. In this way, we can prevent a runway that has not been made available from being used. This measure is part of the Schiphol Safety Improvement Roadmap of the joint sector Integral Safety Management System (ISMS).
Classification: significant incident