What happened
On May 19, 2003, at approximately 15:22 local time, a loss of separation occurred between two commercial aircraft north of Friedrichshafen, on the route between Kempten and NEGRA. The incident involved a Bombardier CL-600-2C10 and a Bombardier CL-600-2B19.
Both aircraft had departed from Munich earlier that afternoon, with the CL-600-2C10 en route to Marseille and the CL-600-2B19 en route to Madrid. During the climb, both aircraft were instructed by Munich radar to transition to Swiss radar control. Upon contacting the new controller, the pilot of the CL-600-2C10 was asked for their desired cruising altitude. The crew responded with FL330 and began climbing to that level. However, the controller had not issued an actual clearance for FL330.
As the CL-600-2C10 climbed, it intercepted the flight level of the CL-600-2B19, which was climbing to FL280. The aircraft passed through the other's altitude with a lateral separation of only 1.6 NM. The crew of the CL-600-2B19 noticed the proximity of the other aircraft and alerted the controller, who subsequently ordered the climb of the CL-600-2B19 to be halted at FL290.
The investigation
The investigation, conducted by the relevant foreign authority, examined radio communications and radar records. The analysis focused on the sequence of instructions between Munich radar, Swiss radar, and the flight crews to determine why the aircraft deviated from their assigned altitudes.