What happened
On October 29, 2005, a Ukraine International Airlines Boeing 737-300 (registration UR-GAL) and a Lufthansa German Airlines Airbus 321 (registration D-AIRL) experienced a loss of separation while descending toward Madrid. Both aircraft were following the same track during their descent phase.
At approximately 10:12 UTC, the Madrid Area Control Centre (LECM) instructed the Boeing 737-300 to increase its rate of descent to 2,000 ft/min or more to reach flight level 210. While the crew read back the new flight level, they did not acknowledge the specific instruction regarding the descent rate, and the air traffic controller (ATCO) did not request a formal acknowledgment of that specific parameter. Simultaneously, the Airbus 321 was instructed to maintain flight level 260.
Shortly thereafter, the Airbus 321 crew received a TCAS Traffic Advisory (TA), followed by a TCAS Resolution Advisory (RA) instructing them to climb. The crew complied, climbing to flight level 265. The Boeing 737-300 crew also performed a TCAS RA maneuver, descending to maintain separation. Radar data indicated that the minimum vertical separation between the two aircraft dropped to approximately 700 feet during the event. No injuries or aircraft damage were reported.
The investigation
The investigation examined radar data, flight data recorder (DFDR) information from the Boeing 73 and-300, and air traffic control communications. The investigation established that the Airbus 321 was descending at a rate of 2,200 ft/min, significantly faster than the Boeing 737-300, which was descending at 1,200 ft/min.
Investigators found that the Boeing 737-300 crew likely did not realize the severity of the event or report the RA maneuver because they were in the process of switching radio frequencies to Madrid Approach at the time the conflict occurred. Furthermore, the investigation noted that the ATCO provided an instruction regarding the aircraft's position without including a call sign, which went unacknowledged.
Findings
- The primary cause of the separation infringement was that air traffic control instructions were issued too late to allow for a timely reaction by both aircraft.
- The Airbus 321 crew did not reduce their high rate of descent despite observing the conflicting traffic below them.
- The ATCO failed to request a specific readback for the required descent rate for the Boeing 737-300 and failed to use a call sign during a critical traffic update.
- Neither the controller nor the supervisory personnel reacted promptly to the automated conflict alert warnings (CPA/CVA) generated by the radar system.
- The Boeing 737-300 crew did not follow standard reporting procedures for a TCAS RA, mistakenly treating the event as a nuisance warning.