What happened
On January 5, 2022, at approximately 03:29 UTC, a serious air traffic incident occurred in Chilean airspace, roughly 35 nautical miles south of the SORTA intersection on airway UL7780. The event involved two Boeing aircraft operating in opposite directions.
Flight DAE1557, traveling from Miami to Santiago, was cruising at FL350. At the same time, flight AAL940, traveling from Santiago to Dallas Fort Worth, was operating at FL360. The Air Traffic Controller (ATCO) at the Oceanic Control Area Center (ACCO) authorized DAE1557 to climb to FL370. However, the controller was unaware that AAL940 was approaching the same intersection from the opposite direction.
As the aircraft approached each other, the vertical separation dropped to just 300 feet. The onboard Traffic Alert and Collision Avoidance System (TCAS) issued Resolution Advisories (RA) to both crews. To avoid a collision, AAL940 was forced to climb 500 feet, while DAE1557 was forced to descend. The incident was only identified after the Lima Control ATCO reported that AAL940 had experienced a TCAS RA.
The investigation
The investigation by DGAC Chile examined radar data, audio recordings of pilot-controller communications, and coordination logs between the ACCO and Lima Control. Investigators analyzed the radar presentation, specifically noting the use of a "pseudo-track" for DAE1557, which represents an aircraft not currently under active radar coverage but calculated based on previous parameters.
Investigators reviewed the handover process between controllers and the controller's monitoring of flight progress strips. The investigation also looked into the communication coverage in the SORTA sector, noting that the ATCO had previously instructed AAL940 to switch to Lima Control due to poor communication range in that specific area.
Findings
- The primary cause of the incident was the ATCO's failure to use procedural control techniques to ensure separation in an area lacking continuous radar coverage.
- The controller authorized the climb of DAE1557 without verifying the crossing time with the oncoming AAL940.
- The controller relied on a pseudo-track for separation purposes, which was unreliable because the radar signal for AAL940 had been lost.
- The controller failed to notice that the flight progress strips indicated a potential conflict and did not calculate the estimated time of crossing.
- There was a lack of permanent radar and communication coverage in the SORTA sector, contributing to the difficulty in maintaining situational awareness.
- The controller did not observe the crossing of the aircraft on the flight progress strips.
Safety action
- The investigation recommends that pseudo-tracks should not be used for active air traffic control due to the high risk of operational errors.
- There is a need to update procedures regarding the use of pseudo-tracks and to reinforce procedural control techniques.
- It is suggested that international studies be conducted to establish protocols for sharing radar signals between adjacent control centers, such as ACCO and Lima Control.
- Recommendations include periodic retraining for controllers regarding flight progress strip marking, workload management, and handover procedures.
- The investigation suggests avoiding scenarios where ATCOs work alone and instead prioritizing teams of two or more controllers during shifts.