Incident Overview
On May 19, 2003, at approximately 15:22 local time, a serious airprox event occurred north of Friedrichshafen, Switzerland, along the route between Kempten and NEGRA. The incident involved two commercial aircraft: a Bombardier CL-600-2C10 and a Bombardier CL-600-2B19. Both aircraft had departed from Munich, with the CL-600-2C10 bound for Marseille and the CL-600-2B19 heading to Madrid. The event was classified as a serious disturbance with no injuries or damage to the aircraft.
Sequence of Events
The CL-600-2C10 was cleared by Munich Radar to Flight Level 260 (FL260). Four minutes later, at 15:19:09, the crew was instructed to switch to Swiss Radar. Simultaneously, the CL-600-2B19 was instructed at 15:16:13 to climb to FL280 and switched to Swiss Radar at 15:20:13. Both crews reported climbing to their assigned levels. Upon identification by Swiss Radar, the controller asked the CL-600-2C10 crew for their desired flight level. The crew selected FL330 and began climbing without receiving an explicit clearance from the controller.
Contributing Factors
The investigation determined that the incident was caused by the CL-600-2C10 crew misinterpreting the controller's query about their desired flight level as a clearance to climb. Consequently, they continued climbing toward FL330 instead of holding at FL260 as originally instructed. The mutual monitoring (closed-loop) procedure failed to prevent the event because both crews were involved in the communication error. The CL-600-2B19 crew observed the approaching aircraft and reported it, prompting the controller to stop the climb at FL290. The separation was reduced to 1.6 nautical miles laterally as the CL-600-2C10 penetrated FL280.