What happened
On March 26, 2003, at 14:13 UTC, a serious airprox incident occurred within the Zurich control zone, approximately 6.6 NM northwest of the runway 14 threshold. The aircraft involved were a Canadair CL-604 Challenger (registration HB-JRC), operating an ambulance flight for Swiss Air Ambulance, and a Pilatus PC-6 Turbo Porter (registration HB-FKP), operated by Swissboogie.
The HB-JRC was conducting an instrument approach (ILS) to runway 14 under IFR. Simultaneously, the HB-FKP was operating under VFR, flying a route intended to take it outside the control zone. During the approach, the air traffic controller at Zurich Approach West provided traffic information to the HB-JRC crew regarding an aircraft crossing their path. The crew of the HB-JRC established visual contact and managed to adjust their descent rate to maintain separation. Radar data later confirmed that the two aircraft came within a horizontal distance of 0.3 NM of each other.
The investigation
The investigation examined radar tracks, radio communications, and pilot statements. It was established that the HB-FKP was flying a route that deviated from the pilot's stated intentions. While the pilot believed they were flying outside the control zone and below 3000 ft, radar tracks showed the aircraft had turned southwest, re-entering the controlled airspace near Eglisau and flying through the zone toward Weiach.
Investigators also reviewed the functionality of onboard safety systems. Although the HB-JRC was equipped with a functional ACAS II, the system failed to provide a timely warning because the HB-FKP was operating with its transponder turned off.
Findings
- The HB-FKP was operating within the Zurich control zone without authorization.
- The pilot of the HB-FKP likely lost situational awareness regarding their position, as the actual flight path deviated significantly from the planned route.
- The transponder on the HB-FK0 was not activated, which prevented the HB-JRC's ACAS II from detecting the collision risk.
- The pilot of the HB-FKP maintained a flight altitude that was higher than their intended 3000 ft limit, placing them in the path of the descending jet.
- The close encounter was mitigated by the timely traffic information provided by the controller and the crew's ability to maintain visual separation and adjust their descent.