On Monday 28 September 2020, during parallel approaches to the Zwanenburgbaan runway (36C) and the Aalsmeerbaan runway (36R) in front of 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
A Boeing 737-800 aircraft was on approach from the west with the intention to land on runway 18C-36C (Zwanenburgbaan). The aircraft was flying at an altitude of 1.2 kilometres (4,000 feet). Coming in from the east, a Bombardier A220-100 aircraft was on approach with the intention to land on runway 18L-36R (Aalsmeerbaan). This aircraft was descending to an altitude of 900 metres (3,000 feet).
There were two approach controllers on duty at the time, one assigned to runway 18L-36R (Aalsmeerbaan) and another to runway 18C-36C (Zwanenburgbaan).
The approach aircraft controller for runway 18L-36R (Aalsmeerbaan) instructed the Bombardier to descend to an altitude of 900 metres according to the established procedure for this runway combination. The pilot of the Bombardier confirmed this instruction and then carried it out. The Boeing was already flying at an altitude of 1.2 kilometres, as instructed by the approach traffic controller for runway 18C-36C (Zwanenburgbaan), according to the procedure for this runway combination. The Bombardier was reducing its speed, which resulted in a slower descent. At the moment of turning to intercept the Instrument Landing System (ILS) for the final approach, this created a difference in altitude between the two aircraft that was less than the standard minimum distance of 300 metres (1,000 feet).
The moment when the loss of distance occurred was the moment in which the Bombardier was still on descent to the instructed altitude of 900 metres and the Boeing was already flying at the instructed altitude of 1.2 kilometres.
The minimum distance between the two aircraft was approximately 2.8 kilometres (1.5 nautical miles) horizontally and more than 150 metres (600 feet) vertically. The separation standard for the phase of the final approach in which the aircraft were located at that moment is: 5.5 kilometres (3 nautical miles) horizontally or 300 metres (1,000 feet) vertically. This standard remains in effect until both aircraft have a stable link to the part of the ILS that ensures an ideal flight path (localiser) to land.
Conclusions of the investigation and follow-up actions
The incident occurred because the Bombardier had not yet reached the altitude of 900 metres before the turn to intercept ILS for the final approach on runway 18L/36R (Aalsmeerbaan) and was flying a wider turn. As a result, the Bombardier ended up to the left of the heading for the intercept flight path. The approach controller then instructed the Bombardier to correct the aircraft to the localiser/intercept course.
Based on a number of comparable occurrences, LVNL has conducted an internal investigation to thoroughly analyse all underlying causes of occurrences with parallel approaches at Amsterdam Airport Schiphol. The results of this investigation have led to the implementation of a number of improvements: an additional training module for air traffic controllers regarding the specific procedures for parallel approach, additional attention for pilots by means of an animated video regarding the specific procedures for parallel approach, monitoring of the parallel operation in a dashboard, and the addition of a distance marker on radar display. An investigation is underway on the technical options for further support of air traffic controllers.
Classification: serious incident