Published on
On Wednesday, July 23, 2025, two aircraft approached each other closer than the separation minima permit. The incident took place during the approach to runway 24 at Rotterdam.
LVNL is conducting its own investigation into this incident and has reported it to the Dutch Safety Board, the Human Environment and Transport Inspectorate, and the Public Prosecution Service in accordance with the investigation process.
At Rotterdam The Hague Airport, aircraft take off and land in a southwesterly direction. A Boeing 737-800 (B738) is flying from the east towards Rotterdam and is descending to 2000 feet (approximately 600 meters) in order to intercept the Instrument Landing System (ILS) for landing on runway 24. Behind it, also flying from the east, is a Pilatus PC-12 (PC12), descending to 3000 feet (900 m). The PC12 is flying a few miles south of the B738 and receives a course instruction towards the ILS, behind the B738. The air traffic controller then instructs the PC12 to descend further to 2000 feet and intercept the ILS.
Shortly afterwards, the radar air traffic controller instructs the pilot of the PC12 to reduce speed so that the flight does not fly too close behind the B738. However, this instruction is not heard by the pilot of the PC12 due to a double transmission of radiotelephony on the same frequency. The controller does not notice that the PC12 pilot is not responding to his instruction.
The pilot of the B738 reports that he has stabilized on the ILS and is instructed to switch to the tower controller. At that moment, the PC12 has just crossed the flight path of the B738 and is about to turn to final. The radar controller informs the PC12 pilot that a B737 is flying 5 nautical miles (approximately 9.3 kilometers) ahead of the PC12. The radar controller warns the PC12 pilot about wake turbulence* and indicates that the PC12 pilot may determine the speed himself. At this point, the PC12 has stabilized on the localizer for runway 24. Under these circumstances, the radar controller is responsible for maintaining the correct separation between the two aircraft.
Below is a brief radio conversation between the PC12 pilot and the radar air traffic controller, in which the PC12 pilot indicates that he has experienced brief wake turbulence. The radar air traffic controller alerts the PC12 pilot to the still relatively high speed. The PC12 pilot is busy with the approach procedure and continues to fly at the same speed. This is not corrected by the radar controller and the PC12 is subsequently transferred to the tower controller. The lateral distance to the B738 is then 4.0 nautical miles (approximately 7.4 km) instead of the required 5 nautical miles**.
Shortly afterwards, the PC12 reduces speed as part of the approach. At this point, the radar controller and the tower controller discuss whether or not to abort the PC12's approach. The distance between the two aircraft has now decreased to 3.3 nautical miles (approximately 6 km), after which the radar controller instructs the tower controller to have the pilot of the PC12 perform a go-around. The required separation is then restored. The PC12 is sent back to the ILS and lands without incident.
Classification: serious incident.
* Wake turbulence separation: wake turbulence is air turbulence that occurs behind an aircraft. The heavier the aircraft, the stronger the turbulence behind it. Aircraft are therefore classified into different weight categories. This is taken into account when determining the minimum distance required between two aircraft.
A B738 falls into the 'Medium' wake turbulence category, while a PC12 falls into the 'Light' category. The PC12 flies behind the B738, which means that the minimum separation required during flight must be 5 nautical miles horizontally or 1,000 feet vertically.
** Wake turbulence separation on the ILS: aircraft intercepting the ILS follow a descending flight path at an angle of 3 degrees until they land on the runway. From the moment of interception, the aircraft therefore follow the same flight path . Although there may be 1000 feet between the aircraft at the same moment in time, this does not count as the required 1000 feet altitude separation: the leading aircraft was previously at the same altitude at the same point as the trailing aircraft is now, because the descent path to the runway is exactly the same. Therefore, the minimum required wake turbulence separation between the aircraft involved in this incident is 5 nautical miles of horizontal separation.
The air traffic controller involved identified the separation conflict and attempted to resolve it with a speed instruction. The radar air traffic controller was unaware that his instruction to slow down was not heard and acknowledged by the pilot of the PC12 due to a double transmission of the radio call. Responsibility for the speed of the PC12 had been given to the pilot, while responsibility for resolving the wake turbulence conflict lay with the radar air traffic controller.
The PC12 flew within the required wake turbulence separation minima before a go-around was ordered by the tower controller.
The incident was investigated within LVNL. The findings of the incident, and specifically the application of wake turbulence separation procedures, were discussed with the air traffic controllers involved and brought to the attention of the Rotterdam operational team.
