What happened
On July 9, 2009, at approximately 09:10 UTC, a serious airprox event occurred near the ROBAS waypoint within the Milan East (MIE) sector of Roma Control. The incident involved three commercial aircraft: an Airbus A319-CJ, registration CS-TFU; an Airbus A320, registration G-MIDX; and an Airbus A320, registration F-GKXF.
The sequence began when the controller in charge of the MIE sector received a series of aircraft into the sector. A conflict alert (STCA) first triggered for flight AFR2221 and WHT923P at flight level 360. To resolve this, the controller instructed WHT923P to descend to flight level 350. However, flight BMA8343 was already operating at flight level 350 on an intersecting path. As WHT923P descended, a second STCA alert activated, indicating a conflict between WHT923P and BMA8343.
During the maneuver, the controller issued a heading instruction to WHT923P, but failed to perceive the pilot's read-back, which indicated the aircraft was descending to flight level 350 rather than maintaining its level. This resulted in a medium-severity reduction in separation between WHT923P and BMA8343 (with a closest point of approach of 2.18 NM and 400 feet) and a further reduction in separation between WHT923P and AFR2221 (with a closest point of approach of 3.83 NM and 0 feet). No injuries or aircraft damage were reported.
The investigation
The ANSV investigation focused on the air traffic control (ATC) environment during the handover between the outgoing and incoming Executive Controllers (CTA EXE). The investigation examined the radar interface differences between the Milan and Rome ACC centers, specifically how the data labels were displayed. It also looked into the coordination between the Executive Controller and the Planner (CTA PLN), noting that high workloads often forced the Planner to use telephone communications, which could be difficult to hear over radio transmissions.
Findings
- The primary cause of the event was the failure of the air traffic controller to maintain full situational awareness.
- A critical factor was the handover process between controllers, which relied on mutual professional confidence rather than a detailed sharing of active traffic strategies.
- Strong West-North-West winds caused significant differences in ground speeds between the aircraft, complicating separation management.
- Differences in the radar interface configuration between Milan and Rome ACCs may have hindered the controllers' ability to quickly acquire necessary flight data.
- There was a lack of coordination from the adjacent sector regarding the impact of a direct routing instruction previously issued to WHT9923P.
Safety action
- The ANSV recommended that ENAC and ENAV S.p.A. review handover procedures to ensure a minimum defined overlap period where both the outgoing and incoming controllers are on the same radio frequency to share active strategies.
- A recommendation was made to ENAV S.p.A. to standardize radar interface configurations across different ATC centers to reduce errors caused by ingrained automated habits.
- The investigation suggested evaluating the implementation of Medium Term Conflict Detection (MTCD) software to assist controllers in strategic planning.