What happened
On 22 August 2012, a near collision occurred at Zurich Airport involving a Darwin Airline Saab 2000, registration HB-IZG, and a Sportcrualler aircraft, registration HB-WYC. The Sportcruiser was conducting a training flight consisting of multiple touch-and-go landings on various runways.
While the light aircraft was established on the right-hand downwind for runway 16, the air traffic controller cleared the Darwin Airline flight, DWT 124, for takeoff from runway 28. Shortly after the Saab 2000 lifted off, the controller instructed the Sportcruiser to perform a 360-degree right turn. This maneuver caused the two aircraft to converge closely. The crew of the Saab 2000 received a traffic alert from their TCAS, prompting an increased rate of climb. The aircraft reached a minimum lateral separation of 205 meters and a vertical separation of only 75 ft.
The investigation
The Swiss Accident Investigation Board (SAIB) examined the sequence of events, the air traffic control instructions, and the technical systems involved. The investigation looked into the complexity of the training flight, the air traffic controller's assessment of the traffic, and the effectiveness of the RIMCAS and TCAS systems. The board also reviewed the history of special flights at Zurich Airport and the published visual approach procedures.
Findings
- The primary cause of the incident was the incorrect assessment of the situation by the air traffic controller, who authorized a takeoff on runway 28 while a light aircraft was approaching runway 16.
- Inadequate risk assessment by air traffic control contributed to the event.
- The training flight was highly complex, involving multiple runway changes during a period of increasing traffic volume.
- The TCAS on the commercial aircraft provided no information to the ground controller regarding the presence of the light aircraft, which limited the controller's situational awareness.
- A lack of established experience for visual approaches on runway 16 contributed to the difficulty in planning the traffic flow.
Safety action
Following the investigation, Safety Recommendation No. 481 was issued, stating that the Federal Office of Civil Aviation (FOCA) should work with Zurich Airport and skyguide to define or amend the general conditions for the safe management of special flights.