D2/2011L Airliner Engine Bleed Air System Failure: Serious Incident on a Scheduled Flight on 5 March 2011

On 5 March 2011 at approximately 06:50 a pressurisation failure led to a serious incident on Finnair flight AY831. An Airbus A320-214 airliner, registration OH-LXL with call sign FIN831L, was on a scheduled flight from Helsinki to London. The aircraft departed with Bleed No1 inoperative according to Minumum Equipment List (MEL 36-11-01).The aircraft was flying in Swedish airspace, north of the Island of Öland at Flight Level (FL) 360 (ca. 10950 m) with both air conditioning packs supplied by Bleed No2 and cross bleed valve opened. 10 minutes after reaching cruise altitude, the remaining bleed (Bleed No2) failed. As a result of this, the flight crew had to execute a descent rapidly to a safe altitude.

The serious incident on the OH-LXL was caused by rising Cabin Pressure which, in turn, could have been the result of a failure of the Fan Air Valve (FAV) or Temperature Control Thermostate (TCT) grid filter clogging in the right engine's bleed air system (Bleed No2).
With the other system being inoperative for flight, the cooling capacity of only one system proved insufficient. The pre-cooled air was too hot, therefore the temperature sensor of the system worked as per its design and shut off the overheated system.

The Safety Investigation Authority, Finland recommends that the EASA oblige Airbus S.A.S. to compile all engine bleed air failure-related emergency procedures that pilots use, and display the complete set of instructions on the ECAM.

The Safety Investigation Authority, Finland also recommends that the EASA oblige Airbus S.A.S. to amend the OEB in a manner that clearly segregates the procedures for prior to the flight and during the flight. Additionally Airbus S.A.S. needs to assure that all the appropriate actions included in the OEB are in line with QRH.

D2/2011L Report (pdf, 0.76 Mt)