ASN Wikibase Occurrence # 310028
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| Date: | Wednesday 14 September 2022 |
| Time: | 02:39 UTC |
| Type: |  Boeing 787-9 Dreamliner |
| Owner/operator: | Virgin Atlantic |
| Registration: | G-VBZZ |
| MSN: | 37976/401 |
| Year of manufacture: | 2016 |
| Fatalities: | Fatalities: 0 / Occupants: 165 |
| Aircraft damage: | None |
| Category: | Serious incident |
| Location: | near waypoint ANKOX -
 Indian Ocean
|
| Phase: | En route |
| Nature: | Passenger - Scheduled |
| Departure airport: | London-Heathrow Airport (LHR/EGLL) |
| Mumbai-Chhatrapati Shivaji International Airport (BOM/VABB) | |
| Investigating agency: | AAIB India |
| Confidence Rating: |  Accident investigation report completed and information captured |
Virgin Atlantic flight VS354, a Boeing 787-9 Dreamliner (G-VBZZ), and Air India flight AI912, a Boeing 787-8 (VT-ANM), were involved in a serious airprox incident.
AI912 was maintaining FL390 on airway Route L301 en route from Dubai (DXB) to Mumbai (BOM). VS354 was trailing AI912 on same airway while maintaining FL410.
The PIC of VS354 was undertaking controlled in-flight rest in the crew rest bunk and the cockpit was being manned by the co-pilot as Pilot Flying in the right seat and relief pilot as Pilot Monitoring on the left seat. The aircraft was in the U-5 sector of Mumbai Oceanic Control and maintaining FL410. The U-5 sector is said to have poor VHF coverage as per the statements of the crew.
Both aircraft were data link capable. As per the e-AIP, India, CPDLC is the primary means of communication and VHF/HF is the secondary means of communication for the aircraft successfully logged on to ADS/CPDLC when operating in Mumbai OCC.
The relief pilot who was PM left cockpit to use the bathroom and PF donned the headset. The PF stated to have received descent clearance to FL 340. This coincided with clearance to increase speed to 0.84 MACH sent by CPDLC at 02:37 UTC.
No descent clearance was given by Mumbai and in fact descent clearance at this stage was unexpected and unplanned. Neither was descent clearance given to any other aircraft.
There is possibility that PF of VS354 mistook a broken transmission over VHF as descent clearance and started descent ignoring the fact that no such clearance was issued on CPDLC which was the primary means of communication in the Mumbai OCC.
The PF set the FL to 340 and aircraft started descent. The aircraft continued to descent until it was pointed by OCC-N controller to maintain FL400 over CPDLC.
The minimum vertical separation was reduced to zero as VS354 descended and later climbed back to the assigned flight level while lateral separation reduced to 3 NM. None of the aircraft reported receiving TCAS RA alert.
Probable Cause of the Serious Incident
The incident was probably caused by confirmation bias on part of crew that a descent may be expected, given that traffic below was ahead and higher MACH has been requested. A broken VHF communication was possibly mistaken for descent clearance and descent was initiated by G-VBZZ without obtaining confirmation over CPDLC.
Accident investigation:
 |
|
Sources:
AAIB India
Revision history:
| Date/time | Contributor | Updates |
|---|---|---|
| 02-Apr-2023 06:43 | harro | Added |
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