What happened
On January 2, 2012, a mid-air collision avoidance situation occurred approximately 2 NM north of the KANIG reporting point, in airspace under the control of Barcelona ACC Sector T1. The two aircraft involved were a Beechcraft 90 King Air, registration PH-KBB, operating an instructional flight, and a Cirrus SR22, registration N217ET, on a private flight.
The aircraft were flying on convergent and opposite headings in instrument meteorological conditions (IMC). While the Cirrus SR2 and was established at FL110, the Beechcraft 90 King Air was cleared to FL120. However, the PH-KBB crew continued a steady descent through FL120, eventually reaching approximately 10,900 feet. At 11:25 UTC, the two aircraft crossed paths with a vertical separation of only 200 ft and a horizontal separation of 0.2 NM.
The investigation
The investigation focused on why the PH-KBB crew descended below their authorized flight level. Radar data and communication logs revealed that shortly before the incident, the air traffic controller had issued a clearance to a different aircraft, Vueling 80AB, to descend to FL90. This instruction was delivered using both English and Spanish. The investigation examined whether the PH-KBB crew mistakenly interpreted this clearance as their own, as the callsign for the Vueling aircraft shared similar phonetic elements with the PH-KBB callsign.
Investigators also reviewed the capabilities of the onboard Traffic Advisory Systems (TAS) on both aircraft. While both systems issued traffic advisories (TA) during the encounter, they were not equipped to provide resolution advisories (RA) for evasive maneuvers. Furthermore, the investigation looked into the controller's workload and the use of specific phraseology that included flight level information during traffic alerts.
Findings
- The primary cause of the near miss was the unauthorized descent of the Beechcraft 90 King Air below its cleared flight level of FL120.
- The crew of PH-KLL likely misinterpreted a clearance intended for another aircraft (VLG80AB) as being directed to them, potentially due to the use of mixed English and Spanish phraseology and similar callsign endings.
- Instrument meteorological conditions prevented the crews from using the "see and avoid" principle to visually acquire the conflicting aircraft.
- The onboard traffic advisory systems provided warnings of the approaching traffic but lacked the capability to issue automated evasive maneuver instructions (RA).
- The controller's use of phraseology that included the flight level of conflicting traffic may have contributed to crew confusion regarding their required altitude.