What happened
On 3 March 2003, a Luxair Fokker 50, registration LX-LGC, was operating a scheduled flight from Turin to Luxembourg at flight level FL200. Simultaneously, a formation of four General Dynamics F16 aircraft, operating under the callsign NAF323 from the Royal Netherlands Air Force, was departing Sion for Leeuwen.
While navigating the VALOR BRAVO HIGH PERFORMANCE route, the F16 formation was instructed to maintain FL190. However, the aircraft were climbing through FL127 at an exceptionally high rate. At approximately 10:48 UTC, the military formation crossed the path of the Fokker 50 at a distance of only 1.8 NM. During this period, the F16s were climbing at an average rate of approximately 45,700 feet per minute, reaching speeds near Mach 1.
The flight crew of LX-LGC observed the military aircraft on their TCAS and visually identified the formation passing closely in front of them. The loss of separation lasted roughly 25 seconds, during which the vertical distance between the two aircraft dropped to nearly zero feet.
The investigation
An investigation by the Swiss Transportation Safety Investigation Board (SUST) analyzed radar plots from both civil and military sources. The investigation established that the F16 formation had failed to comply with altitude restrictions at point VALOR, which required a specific flight level. The investigation also examined the performance of safety systems, including the Traffic Collision Avoidance System (TCAS) and the Short Term Conflict Alert (STCA).
Findings
- The primary cause of the incident was the extreme rate of climb performed by the NAF323 formation, which rendered standard collision avoidance safeguards ineffective.
- The F16 pilots likely relied on Minimum Crossing Altitudes (MCA) shown on a map rather than the written altitude restriction for point VALOR, leading them to fly below the required level.
- The vertical speed of the F16s exceeded the technical limits of the Fokker 50's TCAS version 7, which is unable to process threats with vertical speeds exceeding 10,000 feet per minute.
- The radar controller's ability to intervene was limited by the 12-second radar refresh rate, which was too slow to capture the rapid vertical evolution of the fighter jets.
- The F16 formation failed to notify the Sion controller when passing 15,000 feet, delaying the identification of the altitude deviation.