Loss of pressurization Serious incident Boeing 737-809 (WL) B-18612,
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ASN Wikibase Occurrence # 314616
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Date:Thursday 22 July 2010
Time:17:37 LT
Type:Silhouette image of generic B738 model; specific model in this crash may look slightly different    
Boeing 737-809 (WL)
Owner/operator:China Airlines
Registration: B-18612
MSN: 30173/695
Year of manufacture:2000
Fatalities:Fatalities: 0 / Occupants: 96
Aircraft damage: Minor
Category:Serious incident
Location:NE of Taipei -   Taiwan
Phase: En route
Nature:Passenger - Scheduled
Departure airport:Taipei-Taiwan Taoyuan International Airport (TPE/RCTP)
Destination airport:Hiroshima International Airport (HIJ/RJOA)
Investigating agency: ASC
Confidence Rating: Accident investigation report completed and information captured
China Airlines flight flight CI112, a Boeing 737-800, experienced a depressurization while enroute to Hiroshima, Japan.

According to the pilot interviews and Flight Data Recorder (FDR), CM1 informed CM2 of no pressurization at the left hand side at 1712:45 hours at the altitude of 31,000ft. Flight crew checked cockpit pressure vertical speed indication rising 900ft/minute, when the aircraft was passing the altitude of 33,000ft, at around 8,000ft flight crew checked cabin altitude. FDR showed that there was a Master Caution at 17:27:13 hours at the altitude of 35,300ft. When cabin altitude was rising close to 10,000ft, CM2 requested ATC for permission to descend to 32,000ft and informed ATC that the aircraft had cabin pressurization issue. After noting that cabin altitude and the climb rate kept rising, flight crew requested ATC for permission to descend to 10,000ft and to return back. During descent, the aircraft was passing altitude of 36,200ft at 17:29:07 hours and cockpit had warning sound; flight crew performed emergency descent procedures. During descent flight crew found the of oxygen masks already dropped down; at 17:34:29 hours at the altitude of 18,130ft, CM2 called out ‘MAYDAY’ and set the transponder at 7700 and requested to descend to 8,000ft, after clearance and instructions from ATC the aircraft had air turn back to Taoyuan Airport and landed at 18:11 hours Taipei time, without any damage or injury.

Findings Related to Probable Causes
1. At the time of the aircraft dispatch, Flight Maintenance Log Book had recorded the defect of Engine no. 1 (left engine) bleed air system with low pressure. The system had malfunction during climb, though maintenance personnel had performed checks and regarded it as normal. Due to the left bleed air system failure, the left air conditioning pack could not provide sufficient cabin pressure; while a flexible duct ruptured at the air cycle machine outlet of the right air conditioning pack, the right pack could not provide sufficient cabin pressurization compressed air. both packs failed to provide cabin pressure, which led the aircraft lose pressurization during climb.
2. The malfunction of Engine no. 1 bleed-air system was caused by a broken kiss seal from the pre-cooler control valve, which failed to control the pre-cooler to supply cool air, and therefore, the bleed-air system without sufficient cool air auto shut off due to temperature over limit.
3. The rupture of the flexible duct at the outlet of the right air cycle machine might be caused by chaffing of the duct on metal rings under the normal operation of the air conditioning pack.

Accident investigation:
Investigating agency: ASC
Report number: 
Status: Investigation completed
Duration: 11 months
Download report: Final report



Revision history:

02-Jun-2023 18:59 ASN Update Bot Added
04-Jun-2023 16:04 harro Updated

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