On 14 February, during the approach along the Zwanenburgbaan (18C) of Amsterdam Airport Schiphol, two aircraft came closer to each other than is allowed by the separation minima. LVNL is investigating the occurrence and has reported the occurrence to the Dutch Safety Board.
Loss of separation
The horizontal or vertical distance between aircraft in flight is referred to as their ‘separation’. Separation minima have been established to maintain air traffic safety whilst at the same time making optimum use of air space. Air traffic control is responsible for maintaining this minimum separation between aircraft in its control zone. When two aircraft come closer to each other than the separation minima allow, the situation is known as a loss of separation.
The criteria for separation minima have been designed in such a way that they allow enough time to restore the minimum horizontal or vertical distance. An air traffic controller must undertake a number of steps in a very short time:
- detect the loss of separation;
- identify an effective solution;
- communicate that solution to the pilot(s) concerned, in the form of instructions (regarding their altitude, bearing and speed);
- monitor that the pilot(s) follow these instructions so that safe horizontal or vertical distance is restored as quickly as possible.
LVNL’s primary safety task is to maintain the separation of aircraft in the air, and between vehicles and other obstacles when on the ground. Air traffic controllers internally report any safety related occurrence, with the objective to learn lessons from those occurrences, thereby reducing the chance that similar occurrences will take place again in the future. All reported occurrences are investigated by LVNL, as part of LVNL’s ongoing commitment to improve safety.
Description of the situation
An Airbus 319 approaches from the south for a landing on the Zwanenburg runway. At the same time, a Boeing 737 approaches from the east for a landing on the same runway. The approach controller instructs the Airbus to descend to flight level 40 - over 1,200 metres - and the Boeing to 3,000 feet - some 900 metres. By doing so, the approach controller anticipates sufficient vertical distance between the two aircraft.
The approach controller then directs the Airbus towards the west in order for it to turn for a landing on the Zwanenburg runway. At that moment, both aircraft are at the same height, but horizontally at a sufficient distance from each other. Because the turn of the Airbus turns out to be larger than anticipated, the aircraft also come too close together on a horizontal level according to the separation standards.
The air traffic controller then gives both aircraft additional instructions to correct the resulting loss of distance.
The minimum distance is 1.6 nautical miles horizontally - over 2.9 kilometres - and 200 feet vertically - over 60 metres. During the phase of the approach in which the flights are at that moment, the separation distance is 3 nautical miles horizontally - over 5.5 kilometres - or 1,000 feet - about 300 metres - vertically.
The incident was the result of a wider turn than anticipated in combination with the lack of a good height buffer. Immediately after giving additional instructions to both the Boeing and the Airbus, the loss of distance was corrected, with the result that there was no risk of collision.