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 pilot(s) follow these instructions in order that safe seperation is restored as quickly as possible.

To help prevent losses of separation, air traffic controllers have a number technical and procedural aids to warn them when aircraft come too close to one another. These include STCA (short-term conflict alert). Systems aboard aircraft themselves, such as TCAS (traffic collision avoidance system), can also help avoid losses of separation.