On Tuesday 22 March 2016 early afternoon, two aircraft breached the airborne separation minima during their final approaches to Groningen Airport Eelde (GAE). LVNL has reported this incident to the Dutch Safety Board and is conducting its own investigation.
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 airspace. Air traffic control is responsible for maintaining these minimum distances between aircraft in its control zone. When two aircraft come closer to one another than the 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 correct the situation before it presents a serious danger. An air traffic controller faced with a loss of separation 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 in order that safe separation 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.
On Tuesday afternoon, 22 March, a loss of separation occurs between two aircraft within the approach area of Groningen Airport Eelde. An aircraft type SR22 is instructed to hold at beacon SO - Sierra Oscar - at 3000 feet. An aircraft type PA34 makes a procedural turn at 2000 feet, to approach runway 23 via bacon SO. The vertical separation minimum for this situation is 1000 feet.
The loss of separation occurs when the aircraft type SR22 deviates from the instructed level and starts to descend. The SR22 descents to 1300 feet, which results in a vertical separation less than 1000 feet. As soon as the air traffic controller perceives the deviation he instructs the pilot to fly a divergent direction to solve the conflict. Both aircraft landed safely.
The loss of distance came about because the pilot of the type SR22 aircraft had lost control over the plane and could not maintain the allocated height. This resulted in a loss of separation with a type PA34 aircraft that was flying an approach to runway 23.
As soon as the air traffic controller detected the deviation, he immediately issued divergent direction and height instructions. By that time, the pilot of the SR22 had regained control over the aircraft. Both aircraft followed the instructions, whereupon separation was restored and they landed safely.
The minimal distance between the two aircraft was 1.3 nautical miles – almost 2.5 kilometres – horizontally and 0 feet vertically.
All parties worked in combination at the time of the incident. This means that no radar traffic controller was involved. In such cases, a working method has been determined where aircraft are separated vertically at a distance of 1,000 feet, or laterally by means of geographically separated radio beacons.
The air traffic controller acted in accordance with the regulations and restored the requisite mutual distance.
Follow-up as a result of the investigation
The cause of this incident is outside the sphere of influence of air traffic control. No follow-up is therefore necessary in the area of air traffic control.