Synopsis
On 10 November 2023, at 044548 UTC, a serious incident of airprox occurred approximately 3 NM west-southwest of the Aerodrome Reference Point (ARP) of Indira Gandhi International (IGI) Airport, New Delhi. The incident involved two aircraft: Vistara flight VTI946, an Airbus A320-251N registered as VT-TQL, and Ethiopian Airlines flight ETH689, a Boeing 787-800 registered as ET-ATL. Both flights were operating scheduled international services under Instrument Flight Rules (IFR).
Flight Details
Vistara flight VTI946 originated from Ahmedabad (VAAH) at 0337 UTC and was destined for Delhi (VIDP), with an estimated time of arrival of 0445 UTC. The aircraft carried 171 persons on board, including 2 flight crew and 5 cabin crew. Ethiopian Airlines flight ETH689 departed from Delhi (VIDP) at 0445 UTC bound for Addis Ababa Bole International Airport (HAAB), with 56 persons on board, including 2 flight crew and 4 cabin crew. No injuries were sustained by any occupants, and neither aircraft sustained damage.
Operational Conditions
At the time of the incident, IGI Airport was operating in Segregated Dependent Westerly Mode, with Runway 29L designated exclusively for arrivals and Runway 29R for departures. Runway 10/28 was temporarily closed for resurfacing. The weather was daylight with reported wind shear in the area.
Sequence of Events
ETH689 was cleared for take-off from Runway 29R. Simultaneously, VTI946 was on approach to Runway 29L with a Time-To-Threshold (TTT) below the minimum of 90 seconds established by Standard Operating Procedures (SOPs). During its approach, VTI946 initiated a missed approach due to wind shear. The missed approach track of VTI946 intersected with the Standard Instrument Departure (SID) track being followed by ETH689, leading to a loss of separation.
At 044548 UTC, the Traffic Alert and Collision Avoidance System (TCAS) issued a Resolution Advisory (RA) to both aircraft, which the flight crews followed. After the first RA, the Approach Departure Controller provided instructions to ETH689 intended to de-conflict traffic, but these instructions were not suitable for the traffic situation. Consequently, lateral separation between the two aircraft again decreased, triggering a second TCAS RA event. At 044753 UTC, the minimum separation was approximately 0.2 NM horizontally and 400 feet vertically.
Aftermath
Thereafter, the required separation was re-established. ETH689 continued its flight to Addis Ababa without further incident. VTI946 was re-vectored for an Instrument Landing System (ILS) approach to Runway 29L and landed at Delhi Airport at 0504 UTC.
Investigation
The Aircraft Accident Investigation Bureau (AAIB) of India initiated an investigation under Rule 11(1) of the Aircraft (Investigation of Accidents and Incidents) Rules, 2017. The investigation utilized ATS system recorder data, radar recordings, Cockpit Voice Recorder (CVR) and Digital Flight Data Recorder (DFDR) from VTI946, information from operators and the air navigation service provider, as well as statements from air traffic controllers and flight crew of VTI946.