What happened
On the night of March 23–24, 2024, two wide-body aircraft operated by El Al Israel Airlines and Qatar Airways converged on intersecting airways within the Mumbai Flight Information Region (FIR). The El Al Boeing 777-200, registered 4X-ECB, was en route from Ben Gurion to Bangkok, while the Qatar Airways Boeing 777-300ER, registered A7-BOB, flew from Doha to Malé. Both aircraft were cruising at Flight Level 350 (FL350) on airways L875 and L894, respectively, which intersect at the waypoint GOLEM.
According to flight progress strips, the two flights were scheduled to cross this intersection at the same altitude during the early morning hours. Despite adequate time for detection, no flight level change was assigned to either aircraft by the initial controller. The conflict went unnoticed through two watch handovers until a third controller identified the breach at 0206 UTC. At that moment, the longitudinal separation had reduced to approximately 9.1 nautical miles (about one minute of flight time) with zero vertical separation. The controller immediately instructed the El Al aircraft to descend to FL330, resolving the conflict as the aircraft proceeded on diverging routes. Both flights landed safely at their destinations with no injuries or damage reported.
The investigation
The Aircraft Accident Investigation Bureau (AAIB) of India examined the procedural controls used by the Oceanic Control Centre (OCC) South Sub-Sector in Mumbai, which relies on manual strip-based control rather than radar surveillance. Investigators reviewed duty rosters, communication logs, and automated system alerts to reconstruct the sequence of events.
The inquiry established that the initial Duty Air Traffic Controller (DATCO-1), who was also supervising trainees, failed to identify the developing conflict despite having access to flight progress information. Crucially, DATCO-1 did not brief the incoming controller (DATCO-2) about the potential collision risk at GOLEM during the watch handover. DATCO-2 subsequently took over the position but also failed to detect the breach of standard minimum separation minima for 26 minutes. When DATCO-3 assumed control, they recognized the conflict only after an automated alert was triggered by the system, prompting the immediate altitude change.
Findings
The AAIB determined that the primary cause of the serious incident was a departure from basic procedural control techniques. Controllers failed to scan and update flight progress strips for conflict detection and instead relied excessively on secondary automated alerts. This over-reliance was compounded by the fact that pilot position estimates were not entered into the automated system, which prevented the Medium Term Conflict Detection (MTCD) warning from generating earlier.
Additionally, the investigation found that the prescribed procedures for handing over and taking over watch, as documented in the Manual of Air Traffic Services (MATS-1 and MATS-2), were not followed. This non-adherence to safety-critical Standard Operating Procedures (SOPs) meant that critical conflict information was lost during shifts. The lack of adequate supervision of trainee controllers during on-the-job training was also identified as a contributing factor, as the supervising controller did not engage with the developing situation.
Safety action
The AAIB issued several safety recommendations to the Airports Authority of India (AAI) to prevent recurrence. Key actions include:
- Evaluating and improving the effectiveness of watch handover and takeover briefing procedures.
- Mandating the recording of critical conflict information in logbooks during shift changes to ensure continuity of situational awareness.
- Assessing the minimum data inputs required by controllers in automated systems to ensure effective conflict detection tools function correctly.
- Strengthening on-the-job training supervision protocols to ensure instructors actively manage traffic conflicts with trainees.
- Conducting periodic briefings for controllers on the limitations of secondary systems and the necessity of adhering strictly to manual procedural control techniques.