On Monday 3 April an aircraft approaching for the Buitenveldertbaan at Amsterdam Airport Schiphol and a helicopter 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.
A helicopter departed from Schiphol heading for Amsterdam. The pilot requested permission to fly to the south of the axis of the Buitenveldertbaan. The runway controller specified that the helicopter could fly at an altitude of 1,500 feet - somewhat more than 450 metres. The runway controller also said that the Buitenveldertbaan was active and that the pilot would be informed when the helicopter must have exited the approach area to the Buitenveldertbaan, the so-called ILS area. The runway controller coordinated this with the approach controller.
After some time, the helicopter pilot asked permission to climb to 2,500 ft - somewhat more than 760 metres. This was permitted and the runway controller coordinated this with the approach controller.
The helicopter pilot then asked permission to cross the approach area of the Buitenveldertbaan from south to north. The runway controller gave permission for this and instructed the helicopter pilot to also stay out of the ILS area after crossing the area. The runway controller also coordinated this with the approach controller.
About one minute later, the helicopter pilot asked the runway controller for permission to continue to fly to the east. This route falls within the control area of the approach controller and the helicopter had exemption to fly in this area. The runway controller coordinated the intentions with the approach controller and the helicopter pilot was instructed to contact the approach controller.
The helicopter pilot contacted the approach controller and requested permission to continue to fly to the east. The approach controller permitted this as long as the helicopter would remain to the north of the ILS area. The traffic controller also reported that an Airbus A320 aircraft was approaching Schiphol at a distance of 20 nautical miles - somewhat more than 37 kilometres - from the Buitenveldertbaan.
A little later, the approach controller gave both the Airbus pilot and the helicopter pilot information about the presence of the other aircraft. The pilots reported that they both had visual contact. This meant that, both aircraft were visually separated.
After the Airbus had passed, the helicopter pilot requested permission to cross behind the aircraft. That was permitted. A little later, the Airbus pilot reported that there had been a resolution advisory TCAS warning. The Airbus temporarily maintained an altitude of 2,700 ft - circa 823 metres -, after which it continued its descent.
The approach controller realised later that visual separation is appropriate for the control area for which the runway controller is responsible, but not for the separation prescribed for the approach area (radar separation). The traffic controller reported this.
The minimum separation was 1.5 nautical miles horizontally - somewhat more than 2.7 kilometres - and 400 feet vertical (somewhat more than 120 metres). The separation standard in the area that the aircraft were in at the moment of the incident was 3 nautical miles horizontal - approximately 5.5 kilometres - or 1,000 feet - approximately 300 metres - vertical.
The incident was the result of a type of separation that is not appropriate for the control area concerned. Initially the helicopter flew under the control of the runway controller who geographically separated it from the approach area of the Buitenveldertbaan. The approach controller was informed of this. The flight was continued further to the east in the control area of the approach controller. The approach controller intuitively used visual separation between the helicopter and the approaching Airbus, while radar separation is prescribed in this control area.
The pilots of both aircraft were informed of the other’s position and had visual contact. Therefore, safety was not jeopardised, although a TCAS warning was generated, as a result of which the Airbus pilot interrupted the aircraft’s approach for a short period.
The incident was the reason to bring the aspect of types of separation to the attention of the air traffic controllers through an article in the LVNL Safety Magazine.
Classification: major incident