A320 / A320, en route, east of Nashik India, 2022

A320 / A320, en route, east of Nashik India, 2022

Summary

On 21 March 2022, an Airbus A320 level at FL 360 lost separation with another Airbus A320, which continued its descent beyond its cleared level. A predictive conflict alert prompted the controller to issue multiple calls confirming the clearance limit but with no response. When both aircraft tracks crossed at FL 360, lateral separation was reduced to 3.8 nm. It was concluded that the immediate cause of the conflict was the failure of the descending aircraft to respond to ATC alerting calls, but that its origin was an undetected incorrect readback of the descent clearance.

Description

On 21 March 2022, an Airbus A320 (VT-IAY) operated by Indigo on a scheduled domestic passenger flight from Delhi to Mumbai as IGO6261, which had just been cleared to begin descent from FL380, came into close proximity in day VMC with another Airbus A320 (VT-HYD) operated by Air Asia. The Air Asia aircraft was on a scheduled domestic passenger flight from Delhi to Goa as IAD773, which was maintaining FL360 on a crossing track. Minimum lateral separation was 3.8 nm after the descending A320 failed to respond to ATC alerting prompted by activation of a Predicted Conflict Warning (PCW). No TCAS RA was activated, and neither aircraft crew was aware of the loss of separation or notified of it by ATC.

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