Aviation safety investigations & reports

Loss of Pressurisation; 15km north-west of Jindabyne, NSW

Investigation number:
Status: Completed
Investigation completed


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On 9 November 2005 at 0834 Eastern Daylight-saving Time, a Boeing Company 737-7Q8 aircraft, registered VH-VBI, was being operated on a scheduled passenger service from Sydney, NSW to Melbourne, Vic. The aircraft was at an altitude of 40,000 ft (Fight Level 400) when the pilot in command (PIC) noticed the cabin rate of climb indicator suddenly indicate a maximum rate of climb. The PIC disengaged the autopilot and commenced an emergency descent to an altitude of 10,000 ft. When levelled at 10,000 ft, the crew observed that the cabin had repressurised, so they elected to maintain 10,000 ft and continue the flight to Melbourne. There were no reported injuries to passengers or crew.

The PIC reported feeling upset in the stomach and discomfort in the ears before noticing that the cabin rate of climb indicator showed a sudden increase in cabin altitude. Flight data recorder information showed that the aircraft descended to approximately 500 ft below the assigned altitude for 50 seconds. The co-pilot contacted air traffic control and requested an emergency descent to 10,000 ft; when the clearance was obtained the PIC continued the descent.

The PIC attempted to inform the cabin crew of the emergency descent but the announcement was not heard on the passenger address system in the cabin. The cabin crew reported that not all passengers had put their oxygen masks on after the masks were deployed.

The crew observed that at approximately FL300 the cabin altitude was stabilising. At approximately FL230 the cabin altitude was 9.000 ft and the cabin altitude warning ceased.  At approximately FL160 when the cabin altitude was 4.000 ft, the pilot elected to reduce the rate of descent and the cabin supervisor was advised by the copilot that the oxygen masks could be removed. The aircraft levelled off at 10,000 ft approximately 11 minutes after the descent was initiated.

The examination of the pressurisation system revealed that the sudden increase in cabin altitude was due to the positive pressure relief valves opening at a lower pressure than required.

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General details
Date: 09 November 2005   Investigation status: Completed  
Time: 08:32 ESuT    
Location   (show map): 46km S Tanta, (IFR)    
State: New South Wales   Occurrence type: Air/pressurisation  
Release date: 06 February 2007   Occurrence category: Serious Incident  
Report status: Final   Highest injury level: None  

Aircraft details

Aircraft details
Aircraft manufacturer The Boeing Company  
Aircraft model 737  
Aircraft registration VH-VBI  
Serial number 30644  
Type of operation Air Transport High Capacity  
Damage to aircraft Nil  
Departure point Sydney, NSW  
Destination Melbourne, VIC  
Crew details
Role Class of licence Hours on type Hours total
Pilot-in-Command ATPL 3646 6355
Co-Pilot/1st Officer ATPL 1520 15300
Last update 16 February 2016