ASN Wikibase Occurrence # 318252
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| Date: | Monday 21 March 2022 |
| Time: | 15:52 UTC |
| Type: |  Airbus A320-232 (WL) |
| Owner/operator: | IndiGo Airlines |
| Registration: | VT-IAY |
| MSN: | 6336 |
| Year of manufacture: | 2014 |
| Engine model: | IAE V2527-A5 |
| Fatalities: | Fatalities: 0 / Occupants: |
| Aircraft damage: | None |
| Category: | Serious incident |
| Location: | 227 km NNE of Mumbai -
 India
|
| Phase: | En route |
| Nature: | Passenger - Scheduled |
| Departure airport: | Delhi-Indira Gandhi International Airport (DEL/VIDP) |
| Mumbai-Chhatrapati Shivaji International Airport (BOM/VABB) | |
| Investigating agency: | AAIB India |
| Confidence Rating: |  Accident investigation report completed and information captured |
IndiGo Airlines flight 6E6261, an Airbus A320-232 (VT-IAY), and AirAsia India flight IAD773, an Airbus A320 (VT-HYD), were involved in a serious airprox incident in Mumbai airspace, India.
IAD773 was cruising at FL360, when it came in contact with Mumbai Radar at 15:49 UTC after being changed over from Ahmedabad. The aircraft was advised to proceed direct to waypoint MABTA maintaining FL360. Meanwhile 6E6261 was maintaining FL380 when it contacted Mumbai Radar at 15:50 UTC. When radar contact was established, the flight crew requested descent. The Radar controller gave descent instructions to FL370. However, the descent instruction was readback incorrectly by the flight crew as "descent level 310 IFLY6261 confirm" and the same was also acknowledged by the radar controller as "IFLY6261 Affirm". Thereafter, the 6E6261 started descending at a fast rate.
A PCW (Predicted Conflict Warning) was generated when the radar controller was giving heading instructions to the aircraft. The controller checked the data block of flight 6E6261 and observed that the pilot selected altitude (which is displayed on CCWS) was FL310. The radar controller then instructed 6E6261 to check the selected altitude by transmitting "IFLY6261 Mumbai now turn right fly heading 217 and maintain flight level 370 on reaching sir and check your selected altitude 370 was the cleared level". However, there was no response from the flight crew of 6E6261 for this transmission. The radar controller again transmitted 6E6261 to maintain FL370 and again there was no response from the aircraft. By the time the aircraft responded to the subsequent call given by the radar controller it informed that it had already crossed FL370 and had reached FL360 i.e., the same level as that of flight IAD773 which was cruising at FL360. Thereafter, a CCW (Current Conflict Warning) was generated. The standard vertical and lateral (radar) separation got reduced to 0 feet and 3.8 NM respectively.
Probable cause of the incident
The breach of separation occurred due to non-adherence of SOP on the part of flight crew of IGO6261, wherein they were not maintaining listening watch when the area controller transmitted multiple times to maintain FL370 after PCW warning was generated.
Contributory Factors
• Readback error made by the flight crew of IGO6261 to the cleared descent level of FL370 given by the controller.
• Controller not correcting the readback error made by the flight crew of IGO6261 and confirming the cleared descent level as FL310 instead of FL370.
• Crew of IGO6261 were busy in handing over/taking over controls as PIC immediately left the cockpit after co-pilot re-entered the cockpit, which probably led to crew not maintaining listening watch at critical situation.
• Loss of situational awareness on the part of controller who kept on calling IGO6261 which was not responding instead of shifting focus and instructing IAD773 to avoid potential conflict as PCW warning has already generated with aircraft IGO6261 descending at a faster rate.
• High Rate of Descent of IGO6261 which was higher than the prescribed limit for descending to FL370 due to the readback/hearback error.
Accident investigation:
 |
|
Sources:
AAIB India
Location
Revision history:
| Date/time | Contributor | Updates |
|---|---|---|
| 21-Jul-2023 17:09 | harro | Added |
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