What happened
On April 19, 2012, a Fokker 70, registration PH-KZI, was operating a scheduled passenger flight from Schiphol to Sandefjord, Norway. While cruising at FL350 over the North Sea, southwest of the German island of Sylt, the aircraft encountered a sudden conflict with a military jet.
As the aircraft was under the control of Copenhagen Area Control Centre, the controller notified the crew of a fighter jet at a distance of ten nautical miles. Shortly thereafter, the aircraft's Traffic Alert and Collision Avoidance System (TCAS) issued a Traffic Advisory (TA), followed immediately by a Resolution Advisory (RA) commanding the crew to "CLIMB CLIMB." The flight crew responded by disconnecting the autopilot and initiating an aggressive climb. During this maneuver, the crew observed a light grey fighter jet passing just below them. The minimum lateral separation between the two aircraft was recorded at 0.39 nautical miles, with a vertical separation of only 512 feet.
The investigation
The investigation examined the flight paths of both the Fokker 70 and the F-15C (registration LN 84-000019), which was participating in the international military exercise "Frisian Flag." Investigators reviewed the actions of the fighter controller, the communications between the military formation and the control center, and the operational constraints imposed by the exercise.
It was established that the F-15C was operating under tactical radar assistance, where the pilot is responsible for collision avoidance. The investigation also looked into the NOTAMs (Notice to Airmen) published for the exercise and whether the civilian crew had been sufficiently informed of the specific risks posed by the military activity in that sector of the airway.