What happened
On April 24, 2003, at 06:34 UTC, an air traffic incident occurred approximately 13 NM southwest of Kloten within the Zurich TMA. A Pilatus PC-12/45, registration HB-FOQ, was operating a private instrument flight from Zurich to Florence with eight passengers. The aircraft was following the GERSA 3Y standard instrument departure (SID), which required the pilot to cross waypoint ZH559 at an altitude of at least 9000 ft.
Simultaneously, a Swiss Air Force F5F Tiger, registration T-203, was conducting a check flight from Dübendorf to Emmen. The military aircraft was climbing to FL80. During the climb, the HB-FOQ passed waypoint ZH559 at only FL79, failing to meet the minimum altitude requirement.
As the two aircraft progressed, they closed distance rapidly. The pilot of HB-FOQ received a TCAS Traffic Advisory (TA) indicating an intruder at 11 o'clock, 3 NM away, and 800 ft below. The aircraft eventually reached a minimum separation of only 1.9 NM horizontally and 600 ft vertically. The pilot of the HB-FOQ visually identified the intruder as a