Loss of pressurization Serious incident Airbus A330-342 B-HLH, 14 Sep 2008
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ASN Wikibase Occurrence # 76613
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Type:Silhouette image of generic A333 model; specific model in this crash may look slightly different    
Airbus A330-342
Owner/operator:Cathay Pacific Airways
Registration: B-HLH
MSN: 121
Fatalities:Fatalities: 0 / Occupants: 72
Other fatalities:0
Aircraft damage: None
Category:Serious incident
Location:near Taipei -   Taiwan
Phase: En route
Nature:Passenger - Scheduled
Departure airport:Tokyo-Narita Airport (NRT/RJAA)
Destination airport:Taipei-Taiwan Taoyuan International Airport (TPE/RCTP)
Investigating agency: ASC
Confidence Rating: Accident investigation report completed and information captured
Cathay Pacific Airways Flight number CX521, an Airbus A330-300 aircraft, flew from Tokyo-Narita Airport (NRT/RJAA) , Japan to Taipei-Taiwan Taoyuan International Airport (TPE/RCTP).
The flight departed with 72 occupants on board including 59 passengers, 11 cabin crew members and 2 flight crew members.
The aircraft encountered interruptions of the bleed air system supply at 38,544 ft during descent from flight level FL400. Flight crew members conducted an emergency descent and landed safely at Taipei international airport at approximately 19:29. The aircraft was not damaged and none of the 72 occupants were injured.

Finding related to the probable cause:
Due to the THC's grid filter contaminated from which to reduce the muscle air pressure to control fan air valve that resulted in the fan air valve could not open properly to provide sufficient cooling air to pre-cooler. The no.2 engine bleed air valve was shut down automatically due to bleed air overheat. Both air conditioning systems lost the compressed air source and thereby aircraft lost its pressurization capability.

Findings related to the risk include maintenance related as: The repeated defects of the numerous dual bleed air system and number one engine bleed air defects prior to the occurrence revealed the deficiency of the bleed air system' reliability and potential operation risk.

Findings related to flight operation which include: The flight crew premature change of frequency might have caused by distracted by the system failure, confused the similar call signs on the same control frequency and did not adhere to company communication procedures by inadvertently omitting the CX521 flight number at the end of one of the transmissions and that the transmission was stepped on, thus resulted in a lost opportunity for the pilot and the controller to correct the mistake and prevent the premature change of frequency.

Finding related to ATC include: Approach controller should be aware the existing similar call sign situation and follow the ATMP regulation for pilot' distinguishing when the CX521 acknowledged instruction and read back frequency change incorrectly for other aircraft, did not acknowledge the CX521 distress message immediately on Guard frequency until one minute latter, controller did not follow the ATMP request to provide maximum assistance and first priority to distress aircraft; lack of coordination and information exchange internally from both the TPE Tower and the Approach controllers plus TACC controllers failed to receive the CX521 u201CMaydayu201D call at 1859:56 on 121.5 Frequency until 1900:52. Other risk findings include Datum Mt and Mekong. Emergency frequencies unable to cover each other due to the 140NM distance and geographic influence, TACC North Sector guard frequency test omitted the occurrence neighbor area waypoint SALMI. (The omitted way point test may have resulted in TACC controllers missing Mayday call from CX521) and the ATMP English version and Chinese version 2-4-15 regarding emphasizing to aid in distinguishing between similar sounding aircraft are inconsistent.

Finding related to survival factors include: Some cabin crew members whose oxygen mask did not drop down, did not try to open their access panels or using portable oxygen bottle around their seats, Some cabin crew members may not be familiar with the cabin masks design features and operation with regard to pulling down on the cord to activate oxygen flow and not be fully aware of the normal operation of the cabin masks and some cabin crew members who were not to or not able to use their oxygen masks may have misled passengers into thinking that wearing the mask was not required plus the side effects of the chemical oxygen generators did not list in any cabin related manual and training course.



Accident investigation:
Investigating agency: ASC
Status: Investigation completed
Download report: Final report

Revision history:

30-Aug-2010 14:52 harro Added
05-Jun-2021 09:54 harro Updated [Narrative, Accident report]

Corrections or additions? ... Edit this accident description

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