What happened
On 10 August 2023, at 08:34 UTC, a loss of in-flight separation occurred in the Palma terminal control area, Spain, involving a BOEING 737-8AS, registration EI-ENM, operated by Ryanair, and a CESSNA 525 CITATION JET M2, registration D-IPAA, operated by Heron Luftfahrt.
The Ryanair aircraft was flying southbound from Dublin to Ibiza, while the Cessna 525 was en route from Madrid to Palma de Mallorca. Prior to the incident, the Cessna 525 had been transferred from the GXX en-route control sector to the F1X approach control sector. At the time of the conflict, the two aircraft were in different radio contact sectors, despite both being within the GXX airspace.
A controller in the take-off sector identified the potential conflict and alerted the F1X executive controller. Although evasive instructions were issued to the Cessna 5 and the short-term conflict alert (STCA) system provided warnings, the aircraft still experienced a loss of separation. The minimum distance reached was 0.9 NM horizontally and 500 ft vertically. During the encounter, the TCAS on the BOEING 737-8AS activated in resolution advisory (RA) mode, instructing the crew to descend, which they promptly executed. No injuries or aircraft damage were reported.
The investigation
way the CIAIAC examined the sequence of events and the performance of air traffic control services. The investigation focused on the handoff between the GXX and F1X sectors and the effectiveness of the automated conflict alert systems. The investigation also reviewed the role of a third aircraft, operated by TAP Air Portugal, which was following a similar route to the Cessna 525 and indirectly influenced the traffic scenario.
Findings
- The primary cause was that control services did not take effective and timely action to prevent the loss of separation.
- Air traffic controllers performed an incorrect analysis of the traffic scenario in the GXX sector when identifying potential conflicts and transferring the aircraft.
- There was a lack of monitoring regarding the descent rate of the CESSNA 525 CITATION JET M2, as controllers incorrectly assumed the aircraft would maintain a descent rate consistent with their expectations.
- Software limitations within the ENAIRE STCA system prevented the early identification of the potential loss of separation.
- The transfer of the D-IPAA aircraft to the F1X sector was a conflicting transfer that contributed to the loss of situational awareness between the two different radio sectors.