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ASN Wikibase Occurrence # 160381
Last updated: 7 May 2020
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Type:Silhouette image of generic B744 model; specific model in this crash may look slightly different
Boeing 747-409F (SCD)
Owner/operator:China Airlines Cargo
Registration: B-18716
C/n / msn: 33732/1339
Fatalities:Fatalities: 0 / Occupants: 3
Other fatalities:0
Aircraft damage: None
Location:near Taipei -   Taiwan
Phase: En route
Departure airport:Taipei-Taiwan Taoyuan International Airport (TPE/RCTP)
Destination airport:Abu Dhabi International Airport (AUH/OMAA)
Investigating agency: ASC
China Airlines Cargo flight 5621, a B747-400F, registration number B-18716, took off from Taoyuan International Airport at 03:20 Taipei time for Abu Dhabi International Airport. An excessive cabin altitude warning message showed up on the cockpit instruments panel when the aircraft climbed to 30,000 feet, the flight crew immediately performed emergency descent procedures, put on oxygen masks and declared emergency (MAYDAY) to the Taipei Control. The aircraft returned and landed at Taoyuan International Airport at 05:51 without damage and people on board without injuries.
It was found that #3 air condition duct which supply conditioned air to forward cargo compartment fell off from the connection of check valve and duct assembly.

Findings related to probable causes:
1. As the maintenance personnel tried to repair the duct assembly, the materials above and below flange were protruded to form a flat geometry of the flange such that the clamp could not be secured on the flat flange of duct assembly after installation.
2. The recommended tightening procedure of clamp in Aircraft Maintenance Manual lacked instruction on how to tap the coupling.
Therefore, the tightness of coupling might not reach required constant torque value. That caused the clamp could not be secured on the flange
of duct assembly. Under the condition of airplane operation and the 4 usage of pack, the tightness of clamp was insufficient to sustain the
interactions of airplane vibration and the clockwise bending moment resulted from the conditioned air acted on the air condition duct. The
air condition duct fell off from the connection of check valve and duct assembly, conditioned air leaked from the opening of airframe
continuously and caused excessive cabin pressure altitude warning.



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

Revision history:

10-Sep-2013 18:40 harro Added
22-Oct-2014 19:50 harro Updated [Total occupants, Source, Narrative]

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