Synopsis
On 29 February 2020 at 1259 UTC, a serious incident occurred between Air Asia (India) Ltd flight IAD776 (A320, registration VT-CCU) and Indigo flight IGO2124 (A320, registration VT-IAR) in Delhi Approach airspace. The incident involved a loss of standard separation, with the aircraft coming as close as 0.5 NM laterally and 600 feet vertically. Separation was restored within 26 seconds. No injuries or damage were reported.
History of the Flight
IAD776 was operating a scheduled flight from Goa to Delhi, while IGO2124 was operating a scheduled flight from Delhi to Chennai. At 1244 UTC, IAD776 contacted Delhi Approach Controller and was cleared for the RNAV STAR DIPS5F arrival. Due to bad weather, the aircraft deviated to the right of its assigned track. The controller issued descent clearances to FL140, then FL120, and finally FL110. All instructions were correctly read back.
IGO2124 departed from Runway 09 at 1247 UTC, initially cleared to FL90. After departure, it was handed over to Approach Control, which cleared it to climb to FL100. IGO2124 was following the SID AKRIB 5D departure.
Due to adverse weather, aircraft in the area were deviating from their assigned routes, creating complex traffic conditions. At the time of the incident, IGO2124 was maintaining FL100 and IAD776 was descending to FL110. The automation system displayed an alert of a level burst on IAD776, which was neglected by the controller. Subsequently, IAD776 descended below its assigned altitude of FL110 and came into conflict with the reciprocal traffic IGO2124 at FL100.
The radar controller observed system alerts and attempted to resolve the situation, but by then IAD776 reported a Traffic Collision Avoidance System Resolution Advisory (TCAS RA). Both aircraft received RAs and executed the associated maneuvering.
Aircraft and Personnel Information
Both aircraft were Airbus A320s. IAD776 (VT-CCU) was manufactured in 2011, and IGO2124 (VT-IAR) was manufactured in 2014. All flight crew held valid licenses and were qualified for their respective flights. The pilots-in-command of both aircraft held Airline Transport Pilot Licenses (ATPL), and the co-pilots held Commercial Pilot Licenses (CPL) or ATPL as noted. No fatigue factors were identified for the controller or flight crew.
Air Traffic Control and Systems
The radar controller on duty held a valid Terminal licence with endorsements for Aerodrome Control and Approach Control. All automation systems, VHF channels, and ATS surveillance systems at Delhi Airport were reported to be functioning normally. The Short Term Conflict Alert (STCA) system generated a predicted alert, which soon escalated to a violation alert.
Meteorological Conditions
At the time of the incident, weather conditions included visibility of 1800 meters, wind from 030 degrees at 10 knots, temperature 22°C, QNH 1011, with broken cloud layers. The trend indicated temporary wind gusts up to 25 knots associated with thunderstorms and rain.
Conclusion
The standard separation reduced to 0.5 NM laterally and 600 feet vertically. Standard separation was restored in 26 seconds.