What happened
On August 21, 2017, two aircraft approaching Chhatrapati Shivaji International Airport in Mumbai experienced a significant breach of separation. The first aircraft, a B737-800 operated by Jet Airways with registration VT-JBE, was arriving from Calicut and was positioned as the first in the arrival sequence. The second aircraft, an A321 operated by Air India with registration VT-PPL, was arriving from Varanasi and was second in the sequence.
While the Jet Airways flight was performing an orbit to its right, the Approach Radar Controller issued a descent instruction to flight level 100. Simultaneously, the Air India aircraft was maintaining flight level 110. This sequence of instructions led to a reduction in lateral separation to 2.3 NM and vertical separation to just 400 feet. During the descent, the B737-800 received a TCAS Resolution Advisory (RA), while the A321 received a Traffic Advisory (TA).
The investigation
The AAIB India investigation focused on the actions of the Mumbai Approach Radar Controller during a period of high traffic density. The investigation examined radar replays and communication transcripts, revealing that the controller was managing 12 aircraft on departure and 6 on arrival.
Investigators found that the controller was struggling with radar label management, frequently moving the cursor and readjusting data blocks. Furthermore, the investigation identified communication errors, noting that the controller mistakenly addressed the Air India flight using the call sign for IndiGo, which resulted in the crew not complying with certain instructions. The investigation also noted a delay in responding to the Predicted Conflict Warning (PCW) before it escalated to a Current Conflict Warning (CCW).
Findings
- The primary cause was the controller's attempt to combine a descent instruction with an orbiting instruction within a high-density traffic environment.
- The controller experienced a momentary loss of situational awareness, focusing heavily on arrival sequencing at the expense of monitoring the conflict between the two aircraft.
- Ineffective radar label management and frequent cursor adjustments contributed to the loss of situational awareness.
- There was a significant delay in detecting and reacting to the conflict after the initial automated warning was generated.
- Communication errors, specifically misidentifying an aircraft's call sign, hindered effective coordination.