On Friday 24 March, during the parallel approach along the Zwanenburgbaan (36C) and the Aalsmeerbaan (36R), 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.
At Schiphol, the Aalsmeer runway and Zwanenburg runway are both in use for landings from a southerly direction. An aircraft of the type Embraer 190 approaches from an easterly direction to land on the Aalsmeer runway. From the west, a propeller aircraft of the type Bombardier Dash 8 approaches to land on the Zwanenburg runway.
There are two approach controllers on duty. One air traffic controller is handling traffic for the Aalsmeer runway, while the other controller is handling traffic for the Zwanenburg runway.
The air traffic controller for the Zwanenburg runway has instructed the Bombardier to descend to 4,000 feet (over 1,200 metres). 4,000 feet is the height at which aircraft have to turn in for the Zwanenburg runway when the Aalsmeer runway is also in use. The pilot confirms this instruction and a few minutes later, the Bombardier banks at 4,000 feet for the final approach to the Zwanenburg runway.
The approach controller for the Aalsmeer runway instructs the Embraer to descend to 3,000 feet (over 900 metres). This is to ensure that when the aircraft turns towards the Aalsmeer runway, there is 1,000 feet (over 300 metres) separation from the Bombardier which is approaching for a landing on the Zwanenburg runway. This instruction is also confirmed by the pilot, after which the Embraer starts the descent to 3,000 feet.
The Embraer descends less fast than anticipated by the air traffic controller. This means that the Embraer banks at around 4,000 feet – instead of the planned 3,000 feet – for the final approach to the Aalsmeer runway. On its final approach to the Zwanenburg runway, the Bombardier is also flying at a height of 4,000 feet. The pilots on the Bombardier are given information from air traffic control about the Embraer which is banking at their height for the parallel runway. The pilot on the Bombardier confirms that he can see the Embraer.
Both aircraft landed safely.
The remaining separation is 1.6 nautical miles lateral (around 3 kilometres) and 0 feet vertical. The separation standard in the current phase of the approach of the aircraft is 3 nautical miles lateral or 1,000 feet vertical. This standard applies until the moment when both aircraft are stabilised on that part of the instrument landing system that ensures the ideal course (localizer).
The incident occurred because the air traffic controller’s estimated vertical flight profile for the Embraer did not correspond with the actual flight profile. This was acknowledged by air traffic control. Because both aircraft were almost stabilised on the localizer – this happened a few seconds after reaching the minimum separation – and because the pilot of the Bombardier had confirmed that he could see the Embraer, no corrective instructions were given.
Classification: major incident