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Difference between revisions of "Aircraft Pressurisation Systems"

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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==

Revision as of 12:09, 25 May 2011

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

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 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.

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.

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:

  • LJ35, Aberdeen SD USA, 1999 (On 25 October 1999, a Learjet 35, being operated on a passenger charter flight by Sunjet Aviation, crashed in South Dakota following loss of control attributed to crew incapacitation.)
  • B733, en-route, northwest of Athens Greece, 2005 (On 14 August 2005, a Boeing 737-300 was released to service with the cabin pressurisation set to manual. This abnormal setting was not detected by the flight crew involved during standard checks. They took no corrective action after take-off when a cabin high altitude warning occurred. The crew lost consciousness as the aircraft climbed on autopilot and after eventual fuel exhaustion, the aircraft departed controlled flight and impacted terrain. The Investigation found that inadequate crew performance had occurred within a context of systemic organisational safety deficiencies at the Operator compounded by inadequate regulatory oversight.)
  • A320, en-route, north of Öland Sweden, 2011 (On 5 March 2011, a Finnair Airbus A320 was westbound in the cruise in southern Swedish airspace after despatch with Engine 1 bleed air system inoperative when the Engine 2 bleed air system failed and an emergency descent was necessary. The Investigation found that the Engine 2 system had shut down due to overheating and that access to proactive and reactive procedures related to operations with only a single bleed air system available were deficient. The crew failure to make use of APU air to help sustain cabin pressurisation during flight completion was noted.)
  • RJ1H, en-route, South West of Stockholm Sweden, 2007 (On 22 March 2007, climbing out of Stockholm Sweden, the crew of a Malmö Aviation Avro RJ100 failed to notice that the aircraft was not pressurised until cabin crew advised them of automatic cabin oxygen mask deployment.)
  • B762, San Francisco CA USA, 2008 (On 28 June 2008 a Boeing 767-200 being operated as a Public Transport cargo flight by ABX Air (DHL) experienced a ground fire after loading had been completed and all doors closed and just before engine startup at night. The fire was located in the supernumerary compartment of the airplane. This compartment, which is present on some cargo airplanes, is located directly aft of the cockpit and forward of the main deck cargo compartment which is where the toilet, galley, and three non-flight crew seats are located (see diagram below).The flight crew evacuated the aircraft through the flight deck windows and were not injured, but the aircraft was substantially fire damaged and later classified as a hull loss.)

... further results