This information bulletin is designed for cabin crew and will supplement your airline's cabin crew emergency procedures manual and should enhance your knowledge about what can occur during an aircraft depressurisation.

Why are aircraft pressurised?

Modern aircraft are designed to fly at high altitudes. For example, a Boeing 747 aircraft normally cruises at an altitude of 28,000 – 35,000 ft. This is because aircraft consume less fuel and fly in relatively smooth air, avoiding bad weather and turbulence. However, the human body is not designed to survive at such high altitudes so the air pressure inside the cabin must be controlled.

The air pressure inside the cabin cannot usually be kept the same as the ambient air pressure at ground level as doing so would put excessive stress on the aircraft fuselage. Therefore, the cabin air pressure altitude (as measured by the equivalent outside altitude) gradually rises from take-off to a maximum of 8,000 ft during the cruise. During the descent to the destination airport, the cabin pressure altitude is gradually reduced to match the ambient air pressure of the airport. Without a fully functional pressurised cabin, passengers and crew need to use oxygen systems at the altitudes typically attained during cruise.  

What is depressurisation?

Depressurisation, also called decompression, is the reduction of atmospheric pressure inside a contained space such as the cabin of a pressurised aircraft.

Each year, 'responsible persons', as defined in the Transport Safety Investigation Regulations 2003, Part 2.5, provide the Australian Transport Safety Bureau (ATSB) with reports on aviation accidents and incidents, collectively termed occurrences. These reports are used by the ATSB to assist with the independent investigation of occurrences and for identifying safety trends.

This report provides aviation occurrence data for the period 1 January 1999 to 30 June 2009. The data contained herein is dynamic and subject to change pending the provision of new information to the ATSB.

The data will be adjusted biannually to reflect new information received during the reporting period.

This study reviewed safety trends in the Australian aviation charter industry for the period 1 January 2001 to 31 December 2006. It builds on a previous descriptive study that reviewed immediately reportable matters (IRMs) for regular public transport (RPT) aviation operations. Together, charter and RPT operations make up the air transport sector in Australia. Similar to the previous report, a subset of generally more serious IRMs were reviewed including: accidents; violations of controlled airspace (VCA); breakdowns of separation (BOS) and airproxes; fire, smoke, explosions or fumes; crew injury or incapacitation; fuel exhaustion; and uncontained engine failures. Charter flying activity, measured as flying hours and number of charter operators, was also reviewed.

Hours flown in charter operations initially declined over the study period with an increase across 2004 to 2006. However, the number of hours flown in 2006, the latest year reviewed, was not as high as the historical peak in charter hours observed in 1999. The number of charter operators decreased in 2005 and 2006, so fewer operators conducted more of the hours flown in those years.

Total IRMs reported and the IRM categories examined, were generally stable with the exception of accidents. The rate of accidents decreased significantly between 2001 and 2006. Occurrences involving fire, smoke or fumes, and airspace-related occurrences such as VCA and BOS/airprox, remained stable with no statistically significant increase in the rate across 2001 to 2006. The rate of fuel exhaustion occurrences for the period was 0.4 occurrences per 100,000 hours flown. The other IRM categories; crew injury/incapacitation and uncontained engine failures, were rare.

This review provided encouraging data on the charter accident rate, emphasised the stability of the rate of airspace related occurrences, and the rarity of uncontained engine failures and crew incapacitation in charter operations.

This report provides aviation accident and incident, collectively termed occurrence, data for the period 1 January 1998 to 31 December 2008. This data was provided to the Australian Transport Safety Bureau by 'responsible persons' as defined in the Transport Safety Investigation Regulations 2003, Part 2.5. The data excludes non-VH registered operations in the sport aviation category, and is current as at 31 December 2008.

The data will be adjusted quarterly to reflect new information received during the reporting period.

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