What happened
On June 13, 2015, a loss of separation occurred within the Warsaw Area Control Center (ACC) sector involving two aircraft on intersecting courses. The first aircraft, a Boeing 737-800, was climbing to flight level (FL) 380 toward the OGSEN waypoint. The second aircraft, an Airbus A319, was cruising at FL 370 along the LAGAR-POLON-RUDKA route.
At 20:43:55, the crew of the Boeing 737-800 requested and received clearance to climb to FL 380 after passing FL 260. Radar vectors indicated a collision course with the Airbus A319. Shortly after, the Airbus A319 requested a 130-degree turn to avoid cloud cover, which the controller approved.
As the Boeing 737-800 continued its climb, the distance between the two aircraft decreased. At 20:52:05, a Short Term Conflict Alert (STCA) triggered a yellow warning while the Boeing 737-800 was passing FL 374. The controller subsequently instructed the Boeing 737-800 to increase its rate of climb. Despite this instruction, a red STCA alert was triggered at 20:52:20 as the aircraft passed FL 376. The aircraft eventually passed each other with a vertical separation of only 700 feet, failing to maintain the required 1,000-foot minimum.
The investigation
The investigation examined radar data, radio communications, and the operational environment of the Air Traffic Services (ATS) provider. The inquiry focused on the controller's performance, the status of cockpit/radar warning systems, and the workload within the sector at the time of the incident.
Findings
- The air traffic controller had recently returned to duty following a three-day break.
- Traffic density in the sector was at the upper limits of normal capacity.
- The controller's attention was focused on non-conflicting aircraft rather than the climbing Boeing 737-800.
- Increased radio communications were occurring due to aircraft maneuvering to avoid clouds.
- The Medium Term Conflict Detection (MTCD) warning system was disabled.
- The primary cause was an error in air traffic management (ATM) due to the controller'mal assessment of the situation, specifically failing to account for the changing rate of climb of the ascending aircraft.