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Difference between revisions of "Aircraft Pressurisation Systems"

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==Discussion==
 
==Discussion==
  
Aircraft engines become more efficient with increase in altitude, burning less fuel for a given airspeed. In addition, by flying above weather and associated turbulence, the flight is smoother and the aircraft less fatigued. Crews will therefore normally fly as close to the aircraft’s Cruise Ceiling as they can depending on flight rules and any other constraints such as the aircraft oxygen system. In order to be able to fly at high attitudes, the aircraft needs to be pressurised so that the crew and passengers can breathe without the need for supplemental Oxygen.
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Aircraft engines become more efficient with increase in altitude, burning less fuel for a given airspeed. In addition, by flying above weather and associated turbulence, the flight is smoother and the aircraft less fatigued. Crews will therefore normally fly as close to the aircraft’s Cruise Ceiling as they can depending on flight rules and any other constraints such as the aircraft oxygen system. In order to be able to fly at high attitudes, the aircraft needs to be pressurised so that the crew and passengers can breathe without the need for supplemental oxygen.
  
The cabin and cargo holds (or baggage compartments) on most aircraft are contained within a sealed unit which is capable of containing air under pressure higher than the Ambient Pressure outside of the aircraft. Bleed Air from the turbine engines is used to pressurise the cabin and air is released from the cabin by an Outflow Valve. By managing the flow of air through the outflow valve, using a cabin pressure regulator, the pressure within the aircraft can be increased or decreased as required either to maintain a set Differential Pressure or a set Cabin Altitude.  
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The cabin and cargo holds (or baggage compartments) on most aircraft are contained within a sealed unit which is capable of containing air under pressure higher than the Ambient Pressure outside of the aircraft. [[Bleed Air Systems|Bleed Air]] from the turbine engines is used to pressurise the cabin and air is released from the cabin by an Outflow Valve. By using a cabin pressure regulator, to manage the flow of air through the outflow valve, the pressure within the aircraft can be increased or decreased as required, either to maintain a set Differential Pressure or a set [[Cabin Altitude]].  
In practice, as an aircraft climbs, for the comfort of the passengers, the pressurisation system will gradually increase the cabin altitude and the differential pressure at the same time. When the maximum differential pressure is reached then, if the aircraft continues to climb, the differential pressure will be maintained while the cabin altitude climbs. The maximum cruise altitude will be limited by the need to keep the cabin altitude at or below 8,000 ft.
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In practice, as an aircraft climbs, for the comfort of the passengers, the pressurisation system will gradually increase the cabin altitude and the [[Differential Pressure|differential pressure]] at the same time. If the aircraft continues to climb once the maximum differential pressure is reached, the differential pressure will be maintained while the cabin altitude climbs. The maximum cruise altitude will be limited by the need to keep the cabin altitude at or below 8,000 ft.
  
 
A safety valve:
 
A safety valve:
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*acts as a dump valve, allowing the crew to dump cabin air manually.
 
*acts as a dump valve, allowing the crew to dump cabin air manually.
  
A Cabin Altimeter, Differential Pressure Gauge, and Cabin Rate of Climb gauge help the crew to monitor the aircraft pressurisation.  
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A Cabin Altimeter, Differential Pressure Gauge, and Cabin Rate of Climb gauge help the crew to monitor the aircraft pressurisation.
  
 
==Related Articles==
 
==Related Articles==
  
 
*[[Explosive Depressurisation]]
 
*[[Explosive Depressurisation]]
*[[Emergency Depressurisation]]
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*[[Rapid Depressurisation]]
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*[[Gradual Depressurisation]]
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*[[Loss of Cabin Pressurisation]]
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*[[Oxygen Systems]]
 
*[[Hypoxia]]
 
*[[Hypoxia]]
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[[category: Flight Technical]]
 
[[category: Flight Technical]]
 
[[category: Operational Issues]]
 
[[category: Operational Issues]]
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==Accident & Incidents==
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Events held on the SKYbrary A&I database which include reference to the air conditioning system include:
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{{#ask: [[AW Group 1::Air Conditioning and Pressurisation]]
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Latest revision as of 14:07, 26 January 2017

Article Information
Category: Flight Technical Flight Technical
Content source: SKYbrary About SKYbrary
Content control: SKYbrary About SKYbrary

Definition

A system which ensures the comfort and safety of crew and passengers by controlling the cabin pressure and the exchange of air from the inside of the aircraft to the outside.

Discussion

Aircraft engines become more efficient with increase in altitude, burning less fuel for a given airspeed. In addition, by flying above weather and associated turbulence, the flight is smoother and the aircraft less fatigued. Crews will therefore normally fly as close to the aircraft’s Cruise Ceiling as they can depending on flight rules and any other constraints such as the aircraft oxygen system. In order to be able to fly at high attitudes, the aircraft needs to be pressurised so that the crew and passengers can breathe without the need for supplemental oxygen.

The cabin and cargo holds (or baggage compartments) on most aircraft are contained within a sealed unit which is capable of containing air under pressure higher than the Ambient Pressure outside of the aircraft. Bleed Air from the turbine engines is used to pressurise the cabin and air is released from the cabin by an Outflow Valve. By using a cabin pressure regulator, to manage the flow of air through the outflow valve, the pressure within the aircraft can be increased or decreased as required, either to maintain a set Differential Pressure or a set Cabin Altitude.

In practice, as an aircraft climbs, for the comfort of the passengers, the pressurisation system will gradually increase the cabin altitude and the differential pressure at the same time. If the aircraft continues to climb once the maximum differential pressure is reached, the differential pressure will be maintained while the cabin altitude climbs. The maximum cruise altitude will be limited by the need to keep the cabin altitude at or below 8,000 ft.

A safety valve:

  • acts as a relief valve, releasing air from the cabin to prevent the cabin pressure from exceeding the maximum differential pressure,
  • acts a vacuum relief valve, allowing air into the cabin when the ambient pressure exceeds the cabin pressure, and
  • acts as a dump valve, allowing the crew to dump cabin air manually.

A Cabin Altimeter, Differential Pressure Gauge, and Cabin Rate of Climb gauge help the crew to monitor the aircraft pressurisation.

Related Articles

Accident & Incidents

Events held on the SKYbrary A&I database which include reference to the air conditioning system include:

  • B737 en-route, Glen Innes NSW Australia, 2007 (On 17 November 2007 a Boeing 737-700 made an emergency descent after the air conditioning and pressurisation system failed in the climb out of Coolangatta at FL318 due to loss of all bleed air. A diversion to Brisbane followed. The Investigation found that the first bleed supply had failed at low speed on take off but that continued take off had been continued contrary to SOP. It was also found that the actions taken by the crew in response to the fault after completing the take off had also been also contrary to those prescribed.)
  • A320, en-route, west southwest of Karachi Pakistan, 2018 (On 5 March 2018, the crew of an Airbus A320 in descent towards Karachi observed a slow but continuous drop in cabin pressure which eventually triggered an excessive cabin altitude warning which led them to don oxygen masks, commence an emergency descent and declare a PAN to ATC until the situation had been normalised. The Investigation found that the cause was the processing of internally corrupted data in the active cabin pressure controller which had used a landing field elevation of over 10,000 feet. It noted that Airbus is developing a modified controller that will prevent erroneous data calculations occurring.)
  • B744, en-route, South China Sea, 2008 (On 25 July 2008, a Boeing 747 suffered a rapid depressurisation of the cabin following the sudden failure of an oxygen cylinder, which had ruptured the aircraft's pressure hull. The incident occurred 475 km north-west of Manila, Philippines.)
  • B738, en-route, southern Austria, 2010 (On 9 May 2010, Boeing 737-800 being operated by Swedish operator Viking Airlines on a public transport charter flight from Sharm el Sheikh, Egypt to Manchester UK and which had earlier suffered a malfunction which affected the level of redundancy in the aircraft pressurisation system, experienced a failure of the single air conditioning pack in use when over southern Austria and an emergency descent and en route diversion to Vienna were made. There were no injuries to any of the 196 occupants.)
  • E190, en-route, southwest of Turku Finland, 2017 (On 3 December 2017, an Embraer E190 en-route at FL310 was already turning back to Helsinki because of a burning smell in the flight deck when smoke in the cabin was followed by smoke in the flight deck. A MAYDAY was declared to ATC reporting “fire on board” and their suggested diversion to Turku was accepted. The situation initially improved but worsened after landing prompting a precautionary emergency evacuation. The Investigation subsequently attributed the smoke to a malfunctioning air cycle machine. Issues with inaccessible cabin crew smoke hoods and with the conduct and aftermath of the evacuation were also identified.)

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