What happened
On 31 May 2023, at approximately 2000 UTC, two Emirates Airline flights were traversing the Colombo Flight Information Region (FIR) via the L896 air route. The first aircraft, an Airbus 380 with registration A6-EVG (callsign UAE 5CL), was traveling from Sydney to Dubai at flight level 360. Shortly after, a Boeing 77W with registration A6-EGI (callsign UAE 359) entered the same airspace from Jakarta, maintaining flight level 340.
At 2021 UTC, the crew of the Boeing 77W requested a climb to flight level 360 via Controller Pilot Data Link Communications (CPDLC). The air traffic controller approved this request, which placed both aircraft at the same altitude. Because the aircraft were only 15 to 18 nautical miles apart—well below the required 50 nautical mile longitudinal separation standard—a separation breakdown occurred. The controller did not realize the breach had occurred until an ADS update approximately 11 minutes later, at which point the aircraft was descended back to flight level 340 to restore safety.
The investigation
The investigation examined the actions of the air traffic controller and the operational environment within the Colombo Oceanic Control Area. Investigators reviewed the CPDLC message queue, the use of flight progress stripe boards, and the controller's adherence to established communication protocols during aircraft handovers. The inquiry also scrutinized the controller's duty records, noting that the individual had worked over 200 hours in a single month, exceeding prescribed limitations.
Findings
- The primary cause of the incident was the controller providing an unintended instruction to UAE 349, clearing the aircraft to a flight level that eliminated vertical separation from the preceding aircraft.
- The controller failed to update the flight progress stripe board, which hindered effective decision-making.
- An un-cleared queue of CPDLC messages contributed to the loss of situational awareness.
- The controller was operating under significant fatigue, having exceeded monthly hour limitations.
- Inadequate supervision and the timing of controller handovers during peak traffic periods further compromised safety.
- There was a failure to follow published coordination procedures for the transfer of control.