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ASN Wikibase Occurrence # 194705
Last updated: 29 April 2017
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Date:05-JAN-2016
Time:06:32 UTC
Type:Silhouette image of generic B739 model; specific model in this crash may look slightly different
Boeing 737-96NER (WL)
Owner/operator:Jet Airways
Registration: VT-JBZ
C/n / msn: 36539/2596
Fatalities:Fatalities: 0 / Occupants: 191
Other fatalities:0
Airplane damage: None
Category:Serious incident
Location:Yangon Airspace -   Myanmar
Phase: En route
Nature:International Scheduled Passenger
Departure airport:Mumbai-Chhatrapati Shivaji International Airport (BOM/VABB)
Destination airport:Bangkok-Suvarnabhumi International Airport (BKK/VTBS)
Investigating agency: Aircraft Accident Investigation Bureau (India)
Narrative:
Jet Airways flight 9W70 from Mumbai, India to Bangkok, Thailand departed at 04:10 UTC. There were 8 crew members and 183 passengers on board the aircraft. The First Officer was Pilot Flying.
About 2 hours and 10 minutes into the flight, the aircraft was maintaining FL350 and experiencing light turbulence in Yangon Airspace.
Still experiencing light to moderate turbulence, the flight crew requested permission from Yangon ATC to descend to FL310. At about 06:28 UTC the aircraft received the clearance from Yangon ATC to descend to FL310. Following the clearance from
and the airplane commenced descent to FL310.
At 06:29 UTC, while passing FL340, the 'AUTO FAIL' master caution light illuminated for air-conditioning. The pilot in command took over the controls of the airplane. The cockpit crew started to perform the air-conditioning AUTO FAIL Non Normal Checklist. As per checklist the Pressurisation Mode Selector was put to ALTERNATE.
After selecting ALTN mode, the AUTO FAIL light did not extinguish. The Pressurisation Mode Selector was further switched to MANUAL mode as per checklist.
As a part of the Non Normal checklist, the outflow valve control switch needed to be opened or closed as needed to control the cabin altitude and rate. While using the MAN mode it is stated in FCOM procedures to use outflow valve control switch selector momentarily to modulate the outflow valve to avoid large and rapid pressurisation changes. While operating the outflow valve control switch, the CABIN ALT warning horn and light illuminated.
A passenger announcement was made by the flight crew regarding the rapid descent and a MAY DAY call was made to Yangon ATC. The aircraft started descent to FL110 on ATC instructions.
As per cabin crew statements they heard a loud bang sound near R2 door followed by deployment of all the oxygen mask. Considering the distance to planned destination and fuel consumption at FL110, the crew decided to land at the nearest suitable airport which was Yangon, Myanmar.
The aircraft landed safely on runway 21 at Yangon Airport.

CONCLUSION:
1. AUTO FAIL came ON in flight, the crew operated outflow valve in Manual Mode.
2. The Cabin Altitude warning generated as a consequence of crew action of keeping the outflow valve switch in the open position for longer period of time.
3. Cabin Altitude Warning or rapid depressurisation quick actions performed by the crew were not as per Non-normal checklist.
4. Cockpit crew lacked a clear understanding of the usage of outflow valve switch during manual mode operation.
5. Declaration of emergency was delayed.

Sources:

http://dgca.nic.in/accident/reports/incident/VT-JBZ.pdf

Accident investigation:
cover
investigating agency: Aircraft Accident Investigation Bureau (India)
status: Final
number: Final report
released:10 February 2017
duration of investigation: 1 year and 1 months
download report: Final report

Images:


the cabin pressure control system of the aircraft (AAIB India)

Revision history:

Date/timeContributorUpdates
09-Apr-2017 19:07 harro Added
09-Apr-2017 19:10 harro Updated [Narrative]
09-Apr-2017 19:19 harro Updated [Photo, ]

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