What happened
On September 7, 2012, at approximately 07:45 UTC, a serious incident involving a loss of separation occurred within the Prague/Ruzyně (LKPR) control zone. An Air France Airbus A319, operating flight AFR1482 on the LOMKI 4S STAR, was approaching runway 24. Simultaneously, a Czech Airlines Boeint 735, flight CSA77E, was established on the ILS approach for the same runway.
While following the LOMKI 4S arrival, the A319 crew reached the ERASU intermediate approach fix. Although the arrival charts specified that the aircraft should maintain a heading of 062° after ERASU unless otherwise instructed, the crew initiated a turn toward the localizer without ATC instruction. This maneuver placed the A319 on a collision course with the B735, which was at the same altitude.
Air traffic control (ATCo) identified the conflict and issued an instruction to the A319 to turn left to a heading of 060° when the aircraft were 4.1 NM apart. Due to a slow response from the A319 crew, who initially stated they were following the standard arrival, the ATCo had to repeat the left turn instruction when the distance had decreased to 3 NM. The controller then instructed the A319 to climb to flight level 60. Despite these interventions, the horizontal separation between the two aircraft decreased to a minimum of 1.7 NM.
The investigation
The ÚZPLN investigation examined the actions of the A319 crew, the air traffic controller, radio communications, and radar records. The investigation reviewed the navigation documentation used by the crew, which was compliant with the Czech AIP. The investigation also analyzed the Short Term Conflict Alert (STCA) system logs, noting that the separation minimum of 1.9 NM had been breached before the system's intervention could prevent the reduction in separation.
Findings
- The pilot in command (PIC) of the A319 did not accept a suggestion from the first officer to request clarification from ATC regarding the procedure after passing ERASU.
- The A319 crew deviated from the published STAR LOMKI 4S procedure by initiating a turn to the ILS approach without ATC clearance.
- The A319 crew's response to the controller's initial evasive instruction was delayed.
- The primary cause was human error, specifically the failure of the A319 crew to adhere to the established ATS procedures.