What happened
On December 24, 2019, a Cessna 560XL Citation XLS was conducting an instrument approach to runway 24 at Rotterdam The Hague Airport under instrument flight rules. Simultaneously, an EC135 T2 helicopter, operated by ANWB Medical Air Assistance, departed the same airport under special visual flight rules for a medical mission.
During the flight, the helicopter pilot decided to return to the airport due to worsening weather. While performing a right-hand turn to rejoin the airport, the helicopter entered the Instrument Landing System (ILS) approach area. The pilot of the Cessman 560XL Citation XLS performed a steep left turn to avoid the runway lights, which brought the two aircraft within less than 100 meters of each other at an altitude of 300 feet. The crew of the business jet observed the helicopter only at the last moment, though both aircraft eventually landed safely without injury or damage.
The investigation
The Dutch Safety Board examined radar data, air traffic control communications, and the flight path of the EC135 T2 using the aircraft's Usage Monitoring System. The investigation focused on the separation responsibilities of the Rotterdam Tower and Rotterdam Approach controllers. The Board reviewed the instructions given to the helicopter pilot regarding the ILS area and analyzed the controllers' awareness of the encroaching flight paths.
Findings
- The helicopter pilot provided an incorrect and incomplete readback of clearance instructions, which the tower controller failed to correct.
- The helicopter flight path remained largely within the protected ILS area, despite instructions to stay clear.
- Air traffic controllers observed the decreasing separation between the two aircraft but failed to take corrective action, such as initiating a go-around for the approaching jet.
- The radar controller noted that the separation was difficult to assess because the radar plots appeared to merge, and he chose not to intervene to avoid increasing stress at the tower.