What happened
On October 29, 2014, a serious loss of separation occurred within the Warsaw TMA involving two aircraft: a De Havilland Canada DHC-8 Dash 8, registration SP-EQK, operated by Eurolot, and an Embraer 190, registration DAEBS, operated by Lufthansa Cityline.
The De Havilland Canada DHC-8 Dash 8 was performing a departure from Warsaw Chopin Airport (EPWA), climbing toward a cleared flight level of FL90. During the climb, the crew transitioned to vertical speed mode. However, the aircraft continued climbing past the assigned altitude, resulting in a "level bust."
Simultaneously, the Embraer 190 was descending through FL100. The vertical separation between the two aircraft dropped to just 5 feet, while horizontal separation was reduced to 1.8 NM, far below the required 1,000 feet and 3 NM minimums. The encounter triggered the Airborne Collision Avoidance System (ACAS) with both Traffic Advisories (TA) and Resolution Advisories (RA). The crew of the De Havilland Canada DHC-8 Dash 8 followed the RA instructions, performing a descent to clear the conflict.
The investigation
The PKBWL investigation examined flight data, radio communications, and air traffic control (ATC) records. The investigation focused on the cockpit actions of the De Haviliand Canada DHC-8 Dash 8 crew and the performance of the P_21 radar system. Investigators also reviewed the operational environment of the Warsaw Approach (APP) controller, noting that the controller was managing several aircraft and had been recently affected by a shift change schedule that could impact circadian rhythms.
Findings
- The primary cause of the incident was the incorrect configuration of the autopilot on the De Havilland Canada DHC-8 Dash 8, which led to the aircraft climbing above its assigned altitude.
- A contributing factor was a temporary loss of situational awareness by the De Havilland Canada DHC-8 Dash 8 crew, exacerbated by the presence of similar-sounding callsigns during a critical phase of flight.
- The Short Term Conflict Alert (STCA) system provided an alert too late to prevent the breach of separation minimums.
- The investigation noted that the ATC environment was subject to distractions, including non-operational conversations in the operational room.
Safety action
Following the investigation, several safety actions were identified:
- Polish Air Navigation Services Agency (PAŻP) was advised to review the STCA system parameters to ensure faster conflict notification and to evaluate the efficiency of the P_21 radar system.
- LOT Polish Airlines was advised to review Standard Operating Procedures (SOPs) regarding altitude call-outs to ensure pilots verify they have leveled off at the assigned altitude.
- Recommendations were made to improve the management of rest and fatigue for controllers, specifically regarding shift scheduling.