History
On 3 March 2003 at 10:40 UTC, Luxair flight LGL6572, a Fokker 50 operating from Turin to Luxembourg, contacted Swiss Radar Area West sector INS on frequency 125.55 MHz. The radar controller assigned a transponder code, identified the aircraft, and cleared it on route MOLUS-PENDU at flight level FL200. Meanwhile, at Sion airport, the leader of Royal Netherlands Air Force formation NAF323, consisting of four General Dynamics F16s, requested take-off time from Sion Ground. At 10:41, the formation was cleared to its destination via departure route VALOR BRAVO HIGH PERFORMANCE at FL190. After coordination with military radar, the squadron was cleared for take-off from runway 25 at 10:45 and instructed to report passing 15,000 feet. At 10:47:50, the controller informed NAF323 it was 3 miles from point VALOR, which must be passed at FL190. Radar recordings show that by 10:48:23, the leader's aircraft was 1 NM from VALOR and maintaining FL127 for nearly half a minute, with its route perpendicular to LGL6572. Five seconds later, it crossed 1.8 NM in front of the Fokker 50 at an estimated FL164, climbing at an average rate of 45,700 feet per minute. The crossing occurred at 10:48:28. The F16s' airspeed was close to Mach 1, while the Fokker 50's ground speed was 187 knots.
At 10:48:31, the NAF323 leader announced to sector INS. The radar controller confirmed contact and instructed NAF323 to maintain FL190. After readback, the controller requested confirmation of flight level; the STCA had activated. The leader replied that they were passing FL190. During the 29-second radio exchange, radar plots show the squadron remained at FL188 for 4 seconds, climbed to FL198 for 8 seconds, then descended to FL190 at about 3000 ft/min. The Fokker 50 commander reported observing two targets on TCAS approaching rapidly; his copilot saw three military aircraft. At 10:49:00, the Fokker crew inquired about traffic; the controller replied that the traffic should have been at FL190 and was now at that level. Subsequently, both aircraft were handed over to other sectors. The controller later informed LGL6572 that NAF323 had committed an error leading to a critical convergence.
Analysis
The loss of separation between LGL6572 and NAF323 lasted 25 seconds. The minimum lateral distance was 1.5 NM, and the height difference was close to zero feet, though these did not occur simultaneously. Throughout the conflict, the trajectories were diverging. The conflict involved a military formation of fighters and an airliner in civil controlled airspace, with vastly different flight characteristics. The F16s' exceptionally high rate of climb rendered collision avoidance systems less effective.
Cause of the Conflict
Radar recordings show that the military formation passed point VALOR at FL127, not complying with altitude restrictions in the VALOR BRAVO HIGH PERFORMANCE procedure. It is possible that the leader only considered the Minimum Crossing Altitudes on the SID graphic and missed the written restriction on another page. He did not report passing 15,000 feet as instructed. When the controller reported proximity of VALOR, the leader and his wingmen activated afterburners and climbed at an average rate of 45,700 ft/min to FL190, exceeding the assigned flight level and coming into conflict with the Fokker 50 at FL200. Such rates of climb exceed the limits of technical safety systems (TCAS, STCA) and the reaction abilities of the controller and flight crew.
Loss of Safety Nets
TCAS version 7 surveillance is limited to vertical speeds ≤10,000 ft/min; above this, threat declaration is cancelled. The STCA alerted the controller at 10:48:43, 7 seconds after the loss of separation began.