What happened
On 30 August 2025, at approximately 23:47 UTC, a serious airprox incident occurred within the Mumbai Flight Information Region (FIR). Two aircraft, a Turkish Airlines Airbus A330-223F (registration TC-JOO) and a Flydubai Boeing 737 MAX 8 (registration A6-FKR), were operating on reciprocal tracks along route P574. The Turkish Airlines cargo flight was cruising at FL340, while the Flydubai passenger flight was maintaining FL350.
During the flight, the pilot of the Turkish Airlines aircraft entered a period of controlled rest. While the pilot was resting, the First Officer requested a climb to FL360 via Controller-Pilot Data Link Communications (CPDLC). Although Air Traffic Control (ATC) had previously sent an "unable" message due to traffic, a system-generated reminder on the aircraft's display led the First Officer to believe a clearance had been granted. Consequently, the TC-JOO initiated a climb through the flight level occupied by the Flydubai aircraft. This maneuver caused a loss of both vertical and lateral separation, triggering Traffic Advisory (TA) alerts on both flight decks.
The investigation
The AAIB India investigation focused on the communication chain and the cockpit's interpretation of datalink messages. Investigators examined the CPDLC logs and found that the ATC response was transmitted as an independent message without a Message Reference Number (MRN). Because the MRN was missing, the aircraft's onboard system failed to correlate the ATC's refusal with the original request, instead triggering a visual reminder of the initial request.
Further examination of the cockpit environment revealed that the First Officer misinterpreted this reminder as an authorization to climb. The investigation also noted that the pilot in command, who was in controlled rest, was awakened by the TCAS alert and initially attempted to verify the clearance via voice and text, but the climb had already compromised separation.
Findings
- The primary cause of the incident was the crew of TC-JOO initiating a climb without valid ATC clearance due to a misinterpretation of the CPDLC reminder message.
- The ATC response was sent as a standalone message without an MRN, which prevented the aircraft system from correctly linking the refusal to the original request.
- The First Officer was influenced by expectation bias, perceiving the reminder as a positive authorization.
- The lack of cross-verification between the crew during the climb contributed to the separation loss.
- The aircraft were operating in an area without radar surveillance, relying on procedural control.