On Thursday 22 November, during parallel approaches to the Zwanenburgbaan runway (36C) and the Aalsmeerbaan runway (36R) at Amsterdam Airport Schiphol, two aircraft flew closer together than is permitted by the separation minima. LVNL (Air Traffic Control the Netherlands) is conducting an investigation into this occurrence itself and reported the occurrence to the Onderzoeksraad voor Veiligheid (Dutch Safety Board).
Description of occurrence
At Schiphol, the Aalsmeerbaan runway and the Zwanenburgbaan runway are used simultaneously for landings from the south. A Boeing 737 was approaching from the east to land on the Aalsmeerbaan runway, while an Airbus 330 was approaching from the west for a landing on the Zwanenburgbaan runway.
Two approach controllers were on duty: one controller handling the air traffic for the Aalsmeerbaan runway and the other for the Zwanenburgbaan runway.
The Zwanenburgbaan runway controller instructed the Airbus to descend to 4,000 feet (over 1,200 meters). 4,000 feet is the altitude at which air traffic has to turn for the Zwanenburgbaan runway in the event of simultaneous use of the Aalsmeerbaan runway. This instruction was confirmed by the pilot. Several minutes later, the Airbus executed a turn at 4,050 feet to make a final approach onto the Zwanenburgbaan runway.
The approach controller for the Aalsmeerbaan runway instructed the Boeing to descend to 3,000 feet (over 900 meters) in order to ensure that while turning towards the Aalsmeerbaan runway, it would maintain a separation of 1,000 feet (over 300 meters) from the Airbus, which was approaching to land on the Zwanenburgbaan runway. This instruction was confirmed by the pilot.
The Boeing descended at a slower rate than the controller had anticipated, resulting in the Boeing conducting the turn at around 3,850 feet in order to make its final approach to the Aalsmeerbaan runway (rather than the intended 3,000 feet). At that point, the Airbus was flying at 4,050 feet during its final approach to the Zwanenburgbaan runway.
Both aircraft landed safely.
At the moment of the loss of separation, the minimum distance was approximately 1.7 nautical miles (around 3 kilometers) horizontally. During the approach phase at the particular point in the flights in question, the separation norm is 3 nautical miles horizontally, or 1,000 feet vertically. This norm applies until the point at which both aircraft have stabilized according to the localizer (the part of the instrument landing system that establishes the ideal course line). The vertical distance at that moment was 200 feet (over 60 meters).
The occurrence was able to happen because the Boeing 737 was descending at a slower rate than expected by the approach controller. Based on this occurrence and a number of comparable occurrences, Air Traffic Control the Netherlands (LVNL) has conducted an internal investigation to thoroughly analyse all underlying causes of occurrences with parallel approaches at Schiphol Airport. The results of this investigation have led to the implementation of a number of improvements:
- extra attention to the specific procedures for parallel approach by both air traffic controllers and pilots
- exploration of technological options for further support of air traffic controllers
- more detailed monitoring of the parallel operation in order to learn from it.