What happened
On 2 March 2002, a near-miss incident occurred in the airspace approximately 18 NM northwest of Aosta. The encounter involved two aircraft operating under instrument flight rules in visual meteorological conditions: an Alitalia MD11, registration I-DUPE, and an Air Anatolia B737-400, registration TC-ANH.
The Alitalia flight was climbing from flight level 260 toward a cleared level of 280. Simultaneously, the Air Anatolia aircraft was cruising at flight level 290. Although the radar controller had provided traffic information regarding the opposing aircraft, the Alitalia crew experienced a TCAS Resolution Advisory (RA). Following the advisory, the MD11 increased its rate of climb significantly, passing through its cleared altitude and reaching flight level 285.
At the closest point of convergence, the two aircraft were separated by only 500 feet of altitude and 1 NM of lateral distance, with a closing speed of approximately 753 knots. The pilot of the Air Anatolia aircraft reported the aircraft passing very close to his left side, while the Alitalia crew later confirmed they had followed the TCAS "Climb" and subsequent "Descend" instructions.
The investigation
The investigation examined radar data, TCAS recordings, and cockpit communications. Investigators analyzed the flight parameters of the I-DUPE, noting that the rate of climb surged from 1184 feet per minute to 2872 feet per minute during the maneuver. The study also reviewed the performance of the Short Time Conflict Alert (STCA) at the Geneva Area Control Centre, which triggered a proximity alert to the controller only 12 seconds before the aircraft crossed.
Findings
- The primary cause of the incident was the erroneable behavior of the crew of flight AZA622 and the failure of the crew of flight NTL6300 to react to their respective TCAS alerts.
- The Alitalia crew's response to the TCAS RA led them to exceed their cleared altitude of 280.
- The ergonomics of the MD11 TCAS display were found to be sub-optimal, potentially leading to misinterpretations of information.
- Existing traffic avoidance procedures for both airlines were not sufficiently adapted to the specific technical features of TCAS instrumentation.
- There was a lack of coordination between the automated flight systems and the crew, as the automatic pilot was disengaged during the maneuver, and the crew's procedures did not clearly define the roles of the pilot flying and pilot monitoring during an RA.