2004 Airprox Between NetJets Hawker 800XP and Iberia A320 Near Kloten (EC-HAB)

Incident Overview and Location On 21 April 2004, a serious incident (airprox) occurred 6 NM south-west of the KLO DVOR/DME, near Zurich. The incident involved two aircraft: a Raytheon Hawker 800XP, registration CS-DNJ, operating as NJE 2754 for NetJets Transportes Aéreos S.A., and an Airbus A320-214, registration EC-HAB, operating as IBE 3500 for IBERIA Lineas Aéreas de Espana. The event took place at 08:48 UTC. ## Flight Operations and Sequence of Events IBE 3500 was conducting a scheduled flight from Madrid/Barajas (LEMD) to Frankfurt/Main (EDDF). At 08:37:27 UTC, the crew contacted the Zurich M2 sector and was instructed to maintain FL 320 via the route KORED-BERSU-KUDES-LADOL. NJE 2754 was flying from Northolt (EGWU) to Lugano-Agno (LSZA). The aircraft entered the Zurich airspace at FL 350 and was cleared to descend to FL 330 via the TRA-ODINA route. At 08:46:49 UTC, the Radar Executive (RE-M2) issued a clearance to Ryanair flight RYR 3745 to descend to FL 290, to be level over the ODINA waypoint. However, at 08:46:55 UTC, the crew of NJE 2754 responded, reading back the clearance: “Level two nine zero, to be level at ODINA, NJE two seven five four.” The RE-M2 did not correct this readback. Subsequently, RYR 3745 requested confirmation, and the RE-M2 replied, “that is correct, for you and,” before turning attention to another aircraft. ## TCAS Activation and Resolution The NJE 2754 crew initiated a descent based on the perceived clearance. Shortly after leaving FL 330, the crew received a TCAS Traffic Advisory (TA), followed by a Resolution Advisory (RA) to climb. The aircraft climbed to FL 342 and was stabilized at FL 330 by 08:48:38 UTC. Meanwhile, the IBE 3500 crew also received a TCAS TA and had visual contact with the other aircraft. A TCAS RA instructed the A320 to descend. According to the digital flight data recorder, the A320 began descending approximately 10 seconds before the crossing, which occurred at 08:47:47 UTC. At the time of the crossing, the A320 was at 31,760 ft. The aircraft then climbed back, stabilizing at FL 320 by 08:48:38 UTC. ## Contributing Factors The Radar Planner (RP-M2), who had recently taken over the position, noted that the sector was initially staffed with two air traffic controllers. The RP-M2 had briefly left the position for approximately ten seconds to obtain writing materials. Upon returning, the controller heard RYR 3745 requesting confirmation of the descent clearance. The RE-M2’s confirmation led the RP-M2 to believe the situation was resolved. The incident was noted to have developed very quickly, leaving the RP-M2 no opportunity to intervene. The report notes that the RE-M2 had overlooked the fact that NJE 2754 had read back the clearance intended for RYR 3745. The absence of a corrective response from the controller reinforced the NJE 2754 crew’s belief that the clearance was directed to them. Good visibility and TCAS information were cited as contributing to the resolution of the conflict.