On 25 February 2014, three light 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.
LVNL’s primary safety task is to maintain the separation of aircraft from one another, and also from vehicles and other obstacles when on the ground. Air traffic controllers internally report any incidents falling within our area of responsibility, with the aim of learning lessons from them and so reducing the chance that similar occurrences will take place again in the future. All reported incidents are investigated by LVNL, as part of our ongoing commitment to improving safety.
Tuesday 25 February 2014 saw a high volume of training traffic at and around GAE, practising take-off and approach procedures. At one point three training flights (a Trinidad TB20, a Cessna C303 and a Cessna C172) all wished to practise approaches in the vicinity of the airfield. As the first two began their final approaches, there was a loss of separation. The air traffic controller identified this situation and, in order to rectify it, gave the second approaching aircraft additional instructions concerning its course. However, this reduced the separation between the second and third aircraft. In response, the air traffic controller therefore ordered the third one to abandon its approach so as to widen the distance between the flights. All three aircraft landed safely.
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 has completed its investigation into the loss of separation between three light aircraft at Groningen Airport Eelde (GAE). Below is a summary of the incident, with an illustrative infographic.
Tuesday 25 February 2014 saw a high volume of training traffic at and around GAE, practising take-off and approach procedures. Visibility was good. A Socata TB20 Trinidad (TB20) wishing to practise a VOR/DME (VHF omnidirectional radio range/distance measuring equipment) approach from the east was cleared to do so at Beacon SO. A Cessna C303 coming from the north then requested permission to make an ILS (instrument landing system) approach. Finally, a third training flight, a Cessna C172, contacted air traffic control (ATC).
The first aircraft, the TB20, received course instructions to begin its approach. As the TB20 was passing Beacon SO, the C303 was given course instructions intended to position it 3 nautical miles (nm) – the minimum radar separation – behind the TB20. At this point the C172 had just been instructed to fly to Beacon SO, from where it could start its own ILS approach.
However, ATC had failed to appreciate that the TB20 was flying a VOR/DME rather than an ILS approach. As a result, this aircraft turned into its final approach path some 700 metres northwest of the point at which ATC had expected it to do so. This reduced the separation between it and the C303 to just 1.9 nm. The controller immediately instructed the C303 to change course to restore its separation from the TB20, but that in turn resulted in the separation between the C303 and the C172 falling to 2.4 nm. At this point ATC asked the pilot of the C172 if he could see the C303 in front of him. Because the answer to that question was negative, ATC instructed the C172 to abandon its approach. It subsequently received new ILS approach instructions. All three flights continued without further incident and landed safely.
Classification: significant incident