On 4 July 2016, shortly after departure from runway 21 an aircraft deviated from the instructed altitude and route. Therefore the aircraft came close to a second aircraft that departed from the same runway. The 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);
- ensure that the pilot(s) follow these instructions so that safe horizontal or vertical distance is restored as quickly as possible.
LVNL’s primary task with regard to safety is to keep aircraft separate from one another (including aircraft combined with vehicles on the ground). Air traffic control reports all occurrences that take place in practice within LVNL, in order to learn from them and to reduce the risk of such occurrences in the future. Within LVNL, all reported occurrences are investigated in order to be able to continuously improve safety.
Description of the situation
On the morning of 4 July 2016, two aircraft are planned to depart from Maastricht Aachen Airport around the same time, a Piper PA46 and a Raytheon PRM1. Both aircraft depart from runway 21 on a standard departure to the south. The Piper is the first to depart. The air traffic controller allows the Raytheon to start at the moment he can assign an altitude separated from the Piper.
The radar controller gives the Piper a heading instruction in order to leave the standard departure route, so the Raytheon, which has departed, in a later stage of its flight has a free route to climb and is correctly separated from the Piper. However, the pilot of the Piper makes a sharper turn than specified in the heading instruction. The radar controller issues a new heading instruction. The Piper does not respond. At that point, the Raytheon contacts the radar controller, climbing to 2,000 feet - over 600 metres. The Piper still has an altitude of 4,000 feet - over 1,200 metres - at this time. A short time later, the radar screen indicates that the Piper has started on a western heading at an altitude of 2,000 feet - over 600 metres.
The radar controller instructs the Raytheon to make a turn away from the Piper and informs the Raytheon about the Piper's position. The pilot of the Raytheon confirms having a visual of the Piper. A short time later contact with the Piper is re-established. The pilot asks to return to the airport. The Raytheon is instructed to proceed on its route to the south.
The minimum distance between the Piper and the Raytheon was 0.9 nautical miles - over 1.6 kilometres - horizontally, and 200 feet – approximately 61 metres - vertically.
Results of the investigation
The investigation revealed that the situation arose because the pilot of the Piper aircraft lost control of the aircraft. The Piper quickly lost height and deviated from the standard departure route. This caused the Piper and the Raytheon to come closer together than the separation minima prescribe.
The approach controller reacted adequately by ordering the Raytheon to follow a different northward-swerving course. Despite several attempts, the air-traffic controller was unable to make contact with the Piper. However, the air-traffic controller did provide details to the Raytheon about the position of the Piper. Shortly afterwards, the pilot of the Raytheon caught sight of the Piper. The Raytheon followed the curve to the north, which meant there was a greater distance between the two aircraft. Shortly after that, the approach controller made contact with the Piper. The Piper’s pilot expressed a wish to return to the airport and, to that end, the approach controller provided instructions as to which course the aircraft was to follow. Thereafter, the Raytheon was able to follow its own route.
LVNL cannot prevent such exceptional situations occurring. The incident was adequately and effectively detected and resolved. As far as air-traffic control is concerned, no further follow-up action is required.
Classification: major incident.