Loss of separation Rotterdam

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On Tuesday 24 December, an incident took place at Rotterdam The Hague Airport. It concerned an occurrence between an approaching aircraft landing on runway 24 and a helicopter that had just departed but returned due to deteriorating weather. LVNL (Air Traffic Control the Netherlands) has conducted an investigation into this occurrence and reported the occurrence to the Onderzoeksraad voor Veiligheid (Dutch Safety Board).

Description of occurrence

HEMS flight departed for medical flight in Special VFR conditions

A helicopter of the type Eurocopter 35 (EC135T2) departed from Rotterdam Airport (see 1 in figure) under Special Visual Flight Rules (SVFR). These are weather conditions in which pilots fly by sight (and not with the aid of instruments) in Visual Meteorological Conditions (VMC) with limited visibility. In this case, visibility was less than 5 kilometres and/or the cloud ceiling was lower than 1500 metres. The Helicopter Emergency Medical Services (HEMS) flight had a destination in Muiden and requested a direct route. The tower controller gave permission, in consultation with the radar controller for Rotterdam Approach (at Schiphol-East). The helicopter pilot received information about an inbound aircraft and an additional instruction to stay clear of the ILS area on the south-east side of the final approach for runway 24 (see figure). This was confirmed by the helicopter pilot of the HEMS flight to the controller.

Cessna Citation started to land

An aircraft of type Cessna Citation 560X was flying at a distance of 6 NM (approximately 11 kilometres) from runway 24, approaching Rotterdam The Hague Airport. The aircraft was on an ILS approach and descended to 1,000 feet (approximately 300 meters). This flight was executed under Instrument Flight Conditions (IFR); the pilots were in contact with the tower controller and received landing clearance. The flight crew of this aircraft also received information about the departing helicopter from the tower controller.

Return of HEMS flight due to poor visibility

Within two minutes after departure, the HEMS flight reported that the helicopter would be returning due to deteriorating weather conditions. The tower controller instructed the helicopter pilot to make a right turn to return to the airport; this instruction was confirmed by the pilot to the controller. This action would have increased the distance between the Cessna and the helicopter. The helicopter pilot commences the right turn (see 2 in figure). However, rather than making a U-turn, the right turn was prolonged. The pilot did not fly back to the airport in a south-westerly direction, but instead flew perpendicular to its intended route, in a north-westerly direction (see 3 in figure). Due to the low cloud cover, visibility was poor and the helicopter pilot had lost his geographical orientation. Once the helicopter pilot saw the approach lights of the runway, the pilot regained awareness of his position and made a left turn, in the knowledge that an aircraft was flying in on the ILS approach (see 4 in figure). At that moment, the Cessna Citation had already passed the helicopter, and the helicopter passed behind the Cessna.

Meanwhile, the tower controller instructed the helicopter pilot to fly to point Papa – southeast of the airport – which was confirmed by the pilot to the controller. Because the helicopter's manoeuvre deviated from what was expected, the tower controller asked the helicopter pilot to report his position, to which the helicopter pilot replied that he had stayed clear of the ILS area. However, he was not aware of his actual position at that moment, which was within the ILS area.



Minimum distance

The minimum distance between the two aircraft during this occurrence cannot be estimated accurately from the radar data. Radar loses accuracy at lower altitudes, making it impossible to measure an exact distance. Based on the available radar data and the statements from the pilots of the helicopter and the Cessna Citation, we know that the distance between the aircraft was too small.

Results of the investigation

During the occurrence, there were low-hanging clouds at an altitude of about 200 metres and visibility was 4 kilometres. As a result, the tower controller could not visually observe both aircraft. Visual observation is also not required. In SVFR conditions, different procedures are in place for departing VFR flights than in good visibility conditions, in which the tower controller visually monitors the traffic. The pilots of a SVFR flight are responsible for deciding whether the weather conditions are good enough to take off in their opinion. The tower controller's instruction to the helicopter pilot to remain clear of the ILS area was intended to ensure sufficient mutual distance (geographical separation). Upon departure, the helicopter pilot was instructed to take a left turn – take-off towards the south-east – in order to remain clear of the ILS area. Shortly after departure, the helicopter was no longer visible due to low-hanging clouds and the air traffic controller could no longer check whether the helicopter had stayed clear of the ILS area. VFR flights are not separated based on radar. In this case, the radar was only a tool for the tower controller and not a primary way to ensure sufficient safe distance (separation). The ILS area is not visible on radar for the tower controller or the radar controller. The radar controller saw that the track of the approaching helicopter initially remained clear of the ILS and thus of the landing Cessna Citation.


Due to low-hanging clouds, the pilot lost his reference for his position. During the return manoeuvre and the continuation of the right turn, he did not realise that the helicopter was flying into the ILS. Because the helicopter pilot temporarily lost his orientation and thus flew even deeper into the ILS area, the safety buffer between the Cessna and the helicopter was lost. Both aircraft were visible on radar; however, because the radar indication becomes less reliable at low altitudes, the radar positions on the screen shifted and it was unclear to both air traffic controllers which heading the helicopter was flying. As a result, the tower controller was unable to assess the situation properly. In order to maintain a large distance (separation), he instructed the helicopter to fly to the designated fixed route point Papa, but could not know that the helicopter pilot had lost orientation of his own position and therefore could not fly to that point.



The incident was the result of a number of factors. SVFR flights are required to depart via fixed routes (Papa route point). However, SVFR conditions for HEMS flights occur infrequently, which is why the procedure was not often applied. As a result, the exact procedure is not (or no longer) known to every air traffic controller. The helicopter deviated from the instructed route because the pilot temporarily lost his orientation due to low-hanging clouds and therefore flew into the ILS, where another aircraft was present at that time. Due to shifting radar plots, the heading of the helicopter was not clear and neither the tower controller nor the radar controller could accurately assess the situation. The tower controller was also unable to visually observe the two aircraft due to low-hanging clouds. LVNL will update and publish the procedures regarding Special VFR traffic – and ensure awareness of the procedures in LVNL and beyond.


Classification: serious incident


Editorial supplement August 2020

As a result of additional information exchange with the ANWB, LVNL has obtained additional information regarding the route of the Lifeliner (see figure below), and the situation as experienced by the helicopter pilot. The route of the helicopter is based on the systems on board and uses a different source than the radar of LVNL. The image below shows which route the helicopter followed. It has already been mentioned in the text that LVNL's radar is less accurate at low altitudes and that this was the cause of the shifting plots. For that reason, the routes as indicated in the two images deviate from each other. LVNL has also made a number of minor changes in nuance and details in the above text, such as the helicopter type and the nuance between "low-hanging clouds" and "flying in the clouds". Finally, in the image with the radar plot and in the text it has been changed that the pilot avoided high buildings. The helicopter pilot was looking for high buildings for orientation, but they were located elsewhere than previously indicated.


[1]The Instrument Landing System (ILS) area is an area lined up with the runway for the purpose of maintaining sufficient distance (geographical separation) between IFR and VFR flights. VFR flights outside the ILS areas are separated from IFR flights making an ILS approach on the runway concerned