Synopsis
The serious incident occurred on 8 July 2010 at 13:41 UTC near waypoint VANAS, approximately 50 nautical miles south-southeast of Geneva, at flight level FL 320. A Boeing 737-300 (registration D-ABXS, callsign DLH 03K) operated by Deutsche Lufthansa AG on a scheduled flight from Nice to Frankfurt, and an Airbus A319-111 (registration G-EZIY, callsign EZY 529Y) operated by EasyJet Airline Company Limited on a scheduled flight from London Gatwick to Milan Malpensa, experienced a dangerous convergence. The minimum lateral distance was 2.2 NM and minimum vertical distance was 125 ft.
History of the Incident
At 13:31:11 UTC, DLH 03K contacted combined sector L14 of Geneva Area Control Center (ACC) on frequency 134.850 MHz. The aircraft was approaching waypoint IRMAR, climbing through FL 220 to FL 260. The controller cleared it to follow route IRMAR-KINES-DITON and continue climb initially to FL 300, then to FL 320.
In adjacent sector L56, EZY 529Y was cleared at 13:35:43 UTC to leave cruising level FL 390 and descend initially to FL 380 near waypoint GIRKU. The controller then instructed the crew to maintain heading and at 13:37:14 UTC to descend to FL 370. Thirty seconds later, after coordination with sector L14, EZY 529Y was cleared to continue descent to FL 330 with a vertical speed of at least 2000 ft/min. The readback was correct.
At 13:38:20 UTC, the flight crew of EZY 529Y reported traffic below them. The A319 was passing FL 366 at an average descent rate of 1200 ft/min. The controller replied that the traffic was an aircraft more than 5 NM distant at FL 360. The pilots explained that the traffic had generated a Traffic Alert and Collision Avoidance System (TCAS) alert, leading them to reduce their rate of descent. The controller then instructed them to continue the descent.
Aircraft and Crew Information
Both aircraft were certified and equipped for IFR operations. The Boeing 737-300 was registered in Germany, the Airbus A319-111 in the United Kingdom. Crews held valid licenses and met recent experience requirements. Specific flight experience details are documented in the full report.
Air Traffic Control
At the time, Geneva ACC sectors were combined: L1 through L4 as L14 (covering FL 245 to FL 354) and L5 and L6 as L56 (FL 355 and above). The controller handling L14 did not realize that the EZY 529Y crew reported an incorrect cleared flight level during initial contact. The crew also failed to verify the flight level they correctly read back.
Investigation
The incident was notified on 9 July 2010, and the Swiss Aircraft Accident Investigation Bureau (AAIB) opened an investigation on 26 July 2010. France delegated the investigation to Switzerland. The Swiss Accident Investigation Board (SAIB) published the final report.
Causes and Factors
The serious incident is attributable to the dangerous convergence of an aircraft descending below its cleared flight level to the same level occupied by an aircraft crossing on a perpendicular route. Contributing factors included an incorrect flight level entered into the flight management system by the EZY 529Y crew, the controller not realizing the crew reported an incorrect cleared flight level during initial contact, and the flight crew not performing the appropriate verification of the flight level they correctly read back.