What happened
On 10 September 2010, a Darwin Airline Saab 2000, registration HB-IZJ, was conducting a scheduled passenger flight from Zurich to Lugano. While the aircraft was performing a visual approach to runway 19, it encountered a significant traffic conflict. Simultaneously, a Swiss Air Force Pilatus PC-7, registration A-939, was conducting a training mission originating from Locarno.
The flight instructor in the Pilatus PC-7 had requested permission to cross the Lugano control zone at 3,500 feet. Although the air traffic controller provided information regarding two aircraft on final approach, the training aircraft proceeded with the crossing. As the Saab 2000 turned onto its left-hand base leg, the crew received a climb resolution advisory (RA) from the Traffic Alert and Collision Avoidance System (TCAS). This forced the crew to immediately initiate a climb and execute a missed approach procedure. A second aircraft, a Beech 350, also received a TCAS advisory during the encounter.
The investigation
The Swiss Accident Investigation Board (SAIB) examined the flight paths, radar data, and air traffic control communications. The investigation focused on the coordination between the Air Force and Lugano aerodrome control, the procedures for managing VFR traffic within Class D airspace, and the technical performance of the TCAS units on the involved aircraft. The inquiry also reviewed the training and awareness levels of the flight crews regarding the complexities of mixed-use airspace.
Findings
- The primary cause was the convergence of the Air Force training aircraft with a commercial airliner because the flight instructor permitted the trainee pilot to maneuver the aircraft in a manner that endangered the commercial flight.
- The flight instructor and trainee were unaware of the immediate collision threat.
- The air traffic controller issued the crossing clearance without maintaining an adequate overview of the potential danger.
- There was a systemic lack of awareness among flight crews regarding how TCAS operates within Class D airspace.
- Ineffective information exchange existed between the Air Force and the Lugano control center regarding special flight operations.
- The Air Force mission parameters were not sufficiently error-tolerant for operations within the Lugano control zone.
Safety action
The investigation identified a need for improved training regarding the practical implications of TCAS in mixed-use airspace. Specifically, it was recommended that the Federal Office of Civil Aviation ensure training courses provide sufficient knowledge for pilots to understand the consequences of TCAS maneuvers in Class D airspace. Additionally, the investigation suggested developing better methods for updating flight crews on the complexities of flying in mixed airspace.