Ethiopian B788 and Vistara A20N at New Delhi on Nov 10th 2023, loss of separation, TCAS resolutions

Last Update: September 15, 2025 / 15:28:55 GMT/Zulu time

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Photo of Ethiopian Airlines ET-ATL, Boeing 787-8 Dreamliner — Ethiopian Airlines ET-ATL, Boeing 787-8 Dreamliner (Photo credit: airlines470 / Flickr / License: CC by-sa)

Incident Facts

Date of incident
Nov 10, 2023

Classification
Report

Airline
Ethiopian Airlines

Flight number
ET-689

Departure
Delhi, India

Destination
Addis Ababa, Ethiopia

Aircraft Registration
ET-ATL

Aircraft Type
Boeing 787-8 Dreamliner

ICAO Type Designator
B788

An Ethiopian Airlines Boeing 787-8, registration ET-ATL performing flight ET-689 from Delhi (India) to Addis Ababa (Ethiopia) with 50 passengers and 6 crew, departed Delhi's runway 29R.

At the same time a Vistara Airbus A320-200N, registration VT-TQL performing flight UK-946 from Ahmedabad to Delhi (India) with 164 passengers and 7 crew, was on final approach to Delhi's runway 29L when the aircraft encountered windshear prompting the crew to go around.

Missed approach procedures 29L and standard departure route 29R intersect, therefore the separation between the aircraft reduced until TCAS resolution advisories occurred in both aircraft. The separation reduced to 400 feet vertical and 0.2nm horizontal.

On Sep 15th 2025 India's AAIB released their final report concluding the probable cause of the serious incident was:

The serious incident of airprox occurred due to a loss of situational awareness of the Aerodrome Controller (ADC-S2), wherein an aircraft was allowed to take off from Runway 29R even though the arriving aircraft’s Time-to-Threshold (TTT) had already breached the minimum set value of 90 seconds while approaching dependent parallel Runway 29L.

Subsequently, the arriving aircraft, due to an unstabilised approach on finals, initiated a Go-around from Runway 29L and simultaneously the other aircraft got airborne from the parallel Runway 29R which consequently led to intersection of their projected flight paths.

Contributory Factors

The following are identified as contributory factors to the serious incident:

a) Operational Interdependency and Complexity:

The ADC-S2 controller’s dependency, while issuing take-off clearance to aircraft under their jurisdiction, on the position of arriving aircraft on Runway 29L and concurrent operations on Runway 27 under adverse weather conditions created a complex and high-stress environment, increasing susceptibility to human error and compromising decisionmaking.

b) Cognitive Overload on the ADC-S2 Controller:

The ADC-S2 controller was required to manage multiple simultaneous safety-critical tasks at a very busy airport resulted in cognitive overload. This impaired the controller’s ability to effectively prioritize actions and respond to critical situations in a timely manner.

c) Delayed Transfer of Communication During Missed Approach:

The ADC-S1 controller’s delayed transfer of communication to the Approach Departure Controller regarding execution of missed approach, impeded efficient conflict resolution and limited the controller’s ability to manage the situation effectively.

d) Ineffective Conflict Resolution Instructions:

The Departure Controller issued inappropriate resolution instructions to the aircraft involved in the conflict potentially resulted into less separation between both aircraft and escalated the risk of airprox.

e) Inadequate Separation Assurance in SID Design:

The design of the Standard Instrument Departure (Dudum6C) did not adequately ensure positive separation between departing aircraft from Runway 29R and aircraft executing a missed approach from Runway 29L, increasing the risk of loss of separation.