What happened
On September 3, 2001, at 11:26 UTC, a serious airprox event occurred within the Rome TMA, approximately 30 NM northwest of Ostia. The incident involved a Boeing 737-300, registration G-ECAS, operated by British Midland, and an MD-80, registration I-SMEP, operated by Meridiana.
The British Midland flight was climbing through 15,000 feet toward the Elba VOR, while the Meridiana aircraft was descending on a converging path toward the Tarquinia VOR. The aircraft breached separation minimums, reaching a minimum vertical separation of only 200 feet and a minimum horizontal separation of 0.8 NM. The conflict was ultimately resolved by the onboard Traffic Collision Avoidance Systems (TCAS) of both aircraft.
The investigation
The ANSV investigation examined radar data, radio communications, and statements from the pilots and the air traffic controller. The investigation established that both aircraft had been cleared by Rome ACC to fly intersecting trajectories. The controller's intervention via radar only occurred after the Short Term Conflict Alert (STCA) was triggered on the radar screen.
Investigators found that the air traffic controller used non-standard phraseology and failed to provide necessary traffic information. Furthermore, the investigation noted that the first altitude restriction issued to the British Midland flight was not immediately understood by the pilot, and the pilot did not promptly request clarification. The investigation also noted that the event occurred near a shift change for the radar controller and that the pilots failed to use the standard radio phraseology required when performing a TCAS Resolution Advisory (RA) maneuver.
Findings
- The primary cause was the pilot of flight BMA8PK failing to immediately understand an altitude restriction issued by ATC, combined with a lack of prompt confirmation or request for repetition.
- The air traffic controller failed to use standard phraseology and did not provide adequate traffic information.
- The use of Italian language in certain critical communications increased the risk of misunderstanding.
- Both crews failed to follow the prescribed radio communication procedures following the TCAS RA maneuvers.
- The separation breach was mitigated by the TCAS systems and favorable visual meteorological conditions (VMC).