What happened
On July 20, 2014, a CESSNA 1t2, registration OY-AKH, was conducting a VFR cross-country flight from Bornholm to Roskilde. While traversing Swedish airspace, the pilot mistakenly believed they had received clearance to enter the Malmo TMA at 4,000 feet. Simultaneously, a BOEING 737 800, registration SU-GDY, was operating an IFR commercial flight approaching Copenhagen Kastrup at 4,000 feet.
During the flight, a passenger in the CESSNA 172 became ill, causing significant distraction for the pilot. This distraction delayed the pilot's planned descent to an altitude below the Copenhagen TMA boundary. Consequently, the light aircraft entered the controlled Copenhagen airspace at 4,000 feet, placing it on a collision course with the descending airliner. The two aircraft passed in close proximity near Falsterbo, creating a serious risk of collision.
The investigation
The investigation examined the communication between the pilot of OY-AKH and Sweden Control, noting that a transponder code error went unnoticed by air traffic controllers. It was established that the aircraft's transponder was not providing Mode C altitude information to radar or the TCAS of the BOEING 737 800. The investigation also looked into the complex airspace structure and the different roles of air traffic service providers in the region, which may have contributed to the pilot's confusion regarding flight clearances.
Findings
- The pilot of OY-AKH experienced a diverted focus due to a passenger becoming ill in the cockpit.
- The CESSNA 172 was operating without Mode C altitude information, which prevented ATC and the TCAS of the BOEING 737 800 from detecting the altitude conflict.
- The pilot of the light aircraft incorrectly believed they had authorization to fly at 4,000 feet within the controlled airspace.
- The pilots of the BOEING 737 800 likely misperceived the horizontal separation between the two aircraft, which influenced their decision not to take immediate evasive action.
- The complex nature of the local airspace and the different functions of various ATC units contributed to the pilot's misunderstanding of the required procedures.