What happened
On November 17, 2023, two IndiGo Airbus aircraft, an A321-271NX (registration VT-IUO) and an A320-251N (registration VT-ISO), were involved in a serious airprox incident at Indira Gandhi International Airport, Delhi.
Flight IGO 2113, operating from Delhi to Hyderabad, was cleared for departure from Runway 27 using the AKRIB 6A standard instrument departure (SID). Simultaneously, flight IGO 2206 was departing from Runway 29R using the ITBAN 6C SID. During the climb phase, the crew of VT-IUO performed a left turn that deviated from their assigned route, inadvertently heading toward the takeoff path of Runway 29R. This maneuver brought the two aircraft into close proximity, with a minimum vertical separation of only 400 feet and a lateral distance of 1.2 NM. The conflict triggered a Short-Term Conflict Alert (STCA) and prompted both aircraft to perform TCAS Resolution Advisory (RA) maneuvers.
The investigation
The AAIB India investigation focused on the cockpit procedures of the crew of VT-IUO and the effectiveness of ground-based safety nets. Investigators examined flight data, cockpit voice recordings, and air traffic control logs. The inquiry scrutinized the airline's safety management system, noting that the crew had failed to update the Flight Management Guidance System (FMGS) with the correct departure information and had not maintained a sterile cockpit during taxi. The investigation also looked into the frequency of unwarranted STCA alerts at the airport, which occur when the distance between active runways is less than 3 miles.
Findings
- The primary cause was the failure of the crew of VT-IUO to adhere to Standard Operating Procedures (SOP), specifically failing to update the SID in the FMGS after receiving clearance.
- The crew of VT-IUO did not verify SID information during their briefing and failed to monitor heading deviations during the climb.
- The sterile cockpit environment was not maintained during the taxi phase.
- The air traffic controller responded promptly to the conflict alert, successfully preventing a collision by instructing the second aircraft to halt its climb.
- There were identified shortcomings in the operator's reporting system, as some previous SID deviations had not been reported to the DGCA or AAIB.
- Frequent unjustified STCA alerts are occurring due to the proximity of the two runways, and no formal safety risk assessment had been conducted regarding this phenomenon.