Event Details

Title:Pressurization emergency, Final Report No. 1820 by the Aircraft Accident Investigation Bureau concerning the serious incident to the aircraft Airbus A 321-111, HB-IOA, operated by Swissair under flight number SWR 809 on 21 February 2000 during the flight
Micro summary:Pressurization failure on this Airbus A320 triggers an emergency descent.
Event Time:2000-02-21 at 2001 UTC
File Name:2000-02-21-CH.pdf
Publishing Agency:Aircraft Accident Investigation Bureau (AAIB)
Publishing Country:Switzerland
Report number:1820
Site of event:Cruise, 21 minutes after takeoff
Departure:London Heathrow Airport, London, England, United Kingdom
Destination:Zurich International Airport (Kloten Airport), Kloten, Switzerland
Airplane Type(s):Airbus A321-111
Flight Phase:Cruise
Type of flight:Revenue
Serious Injuries:0
Other Injuries:0
Executive Summary:At 19:40 UTC on 21 February 2000, aircraft HB-IOA took off from London-Heathrow on scheduled flight SWR 809 to Zurich-Kloten.

At 20:01 UTC, after a continuous climb of approximately 21 minutes duration and shortly after the aircraft had reached its cruising altitude of flight level (FL) 330, the co-pilot reported a rapid increase in cabin altitude to the commander. The commander noticed that control system 2, which regulates the cabin pressure, was indicating a malfunction. He further discovered that control system 1 did not take over the intended function and that the cabin altitude was increasing further. A little later control system 1 also failed and the outflow valve remained half open, so the air in the cabin could escape unhindered within a very short time. Inside the aircraft, because of this adiabatic expansion, distinct cooling accompanied by condensation was perceived.

When the cabin altitude had exceeded 9550 ft, the "excess cabin altitude" warning in the cockpit was triggered. The commander then decided to initiate an emergency descent immediately. Both flight crew members put on oxygen masks and the co-pilot as pilot flying initiated the descent. The commander reported to air traffic control that SWR 809 was in an emergency situation and subsequently received several clearances for a rapid descent to FL 100. During the following 6 minutes the aircraft descended to the cleared flight level at an average rate of descent of 3800 ft/min. During the descent the flight crew implemented the corresponding ECAM procedure. After the incident the flight crew indicated that throughout the entire event they had not noticed any master caution or master warning. Since the cabin altitude had reached 14,000 ft in the meantime, the oxygen masks in the passenger cabin were released and the passengers were requested by an automatic announcement to put them on.

When HB-IOA reached FL 100, the flight crew took off their oxygen masks and the commander informed the passengers. Since none of the passengers exhibited any adverse health effects and since there was sufficient fuel to continue the flight to Zurich at a lower altitude, the commander decided not to perform a diversion landing and to continue the flight to the destination. The flight crew ascertained that the cabin could be pressurised manually. Since icing conditions prevailed at FL 100 on the remaining segment of the flight to Zurich, a climb to FL 140 was carried out and the cabin pressure was controlled manually. As a precaution, the flight crew asked for a doctor to be present on landing to care for passengers, if necessary. This was not needed.

The landing in Zurich-Kloten took place at 21:01 UTC.

The serious incident is attributable to the fact that because of a known malfunction of a cabin pressure controller, the outflow valve of the pressurised cabin opened and the redundant controller was not able to correct the malfunction.

Learning Keywords:Systems - Pressurization
Other - Manufacturing Issues
Close match:Pressurization emergency, Boeing 737-500 (EI-CDF), near Wallesley, North Wales, January 16, 2001
Rapid decompression, Lockheed L-1011, August 23, 1995


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