Incident Overview
On November 27, 2003, at 07:55 UTC, an airprox incident occurred approximately three nautical miles northwest of the MILPA waypoint within the UAC Geneva sector. The event involved Iberia Flight 3513, an Airbus A320 registered as EC-IEF, and Delta Air Lines Flight 154, a Boeing 763 registered as N194DN. Both aircraft were operating scheduled services; Iberia was en route from Frankfurt to Madrid, while Delta was traveling from New York to Venice.
Sequence of Events
At 07:37 UTC, the crew of IBE3513 contacted Swiss Radar Area West and received a clearance to maintain flight level (FL) 330 on route BENOT-MEBAK. Shortly thereafter, the pilot requested a climb to FL350. The controller indicated that FL350 was occupied but assigned FL340 four minutes later. Despite receiving and reading back the clearance for FL340, the crew erroneously entered FL350 into the Flight Control Unit (FCU) altitude window.
At 07:48 UTC, DAL154 contacted the same sector at FL350 and was cleared on route MILPA-ORSUD-SARONNO. The routes of the two aircraft intersected perpendicularly near MILPA. At 07:53 UTC, the STCA (Short Term Conflict Alert) system triggered an alert. Radar data indicated IBE3513 had climbed to FL343, exceeding its assigned level. The controller immediately issued traffic information to both crews. DAL154 initiated a climb to FL355 in response to a TCAS resolution advisory, while IBE3513 descended back to FL340.
Findings and Analysis
Radar traces recorded a minimum horizontal separation of 4.6 nautical miles and an altitude difference of 600 feet between the two aircraft. The investigation revealed that the controller in charge was a trainee under direct supervision, and traffic load was average. The primary cause of the incident was identified as a crew error: the co-pilot of IBE3513 mistakenly set FL350 in the FCU instead of the cleared FL340. The commander reported being distracted by a cabin check for electronic device interference and system circuit-breaker checks, which likely contributed to the failure to monitor the altitude acquisition.