Aviation Safety Council (ASC) released the investigation report of an EVA Airways (EVA Air) Airbus A330-203 dual pressure regulator sensors failed occurrence.

On December 29, 2010 an EVA Air Airbus A330-203 (bearing national registration number B-16312) was on a scheduled passenger flight from Bangkok International Airport, Thailand to Vienna International Airport, Austria. There were 3 flight crew, 8 cabin crewmembers and 66 passengers on board. During cruise over Ukraine at 40,000 ft, the aircraft had loss of both bleed air systems that caused abnormal cabin pressure. With the ATC guidance the flight crew performed emergency descent procedures to divert to Simferopol International Airport, Ukraine. The aircraft had no damage and all people on board were safe.

According to Aviation Occurrence Investigation Act Article10, ASC forwarded a notification to State Aviation Administration of the Ukraine National after the occurrence. Referring to the Convention of International Civil Aviation Annex 13, on December 30, 2012 State Aviation Administration of Ukraine delegated ASC to proceed the investigation. ASC following Aviation Occurrence Investigation Act and relevant procedures started the investigation. In accordance with the law, those organizations and authorities that were invited to conduct the investigation were Civil Aeronautics Administration, Ministry of Transportation and Communications (CAA), Bureau of Enquiry and Analysis for Civil Aviation Safety, France, Airbus and the civil aviation authorities from Ukraine. The investigation report was reviewed and approved by ASC’s 153rd Council Meeting on March 20th, 2012 and was published on April 20th, 2012 after those concerned organizations and authorities confirmed the content without objection.

There is one ’finding related to probable causes’: Inside the pressure regulator sensors of Engine no.1 and no.2 air bleed systems, moister had accumulated to water due to temperature variation in the environment. During cruise the aircraft was in an extremely low temperature environment, which led the water contained in the pressure regulator sensors to freeze. The sensors of both air bleed systems, affected in succession by icing, generated the erroneous signals of the air bleed pressure; which caused the air bleed monitor computer to erroneously regard the air bleed as over pressure and tshut off the pressure regulator valve which then resulted in the occurrence. ‘Findings related to risks’ include 2 items. After the warning ‘CAB PR EXCESS CABIN ALT’ coming up the flight crew performed emergency descent as per procedure. During descent the flight level was level off at FL280 as ATC requested for separation purpose. Though keeping requesting for a lower flight level, the flight crew did not neither to request for emergency descent nor to declare the emergency situation; therefore the aircraft did not get the most prioritized assistance from the ATC to descend promptly to a safe altitude. According to the information provided by Airbus on flight test data and statistics of the A330, among the pressure regulator sensors in the pylons of General Electric Company (GE), Pratt & Whitney (PW) and Rolls-Royce (RR) engines, there is a higher risk of the air bleed system malfunction when an A330 is fitted with GE engines.

ASC issued 14 Safety Recommendations. Seven recommendations issued to EVA Airways. To mandate pilots to request for emergency descent or to declare promptly the emergency situation to ATC when encountering cabin de-pressurization to obtain the most prioritized assistance. To promote the cases of the twin engine aircraft about loss of both air bleed systems to improve the alertness and emergency reaction to the similar situations. To perform an A330 fleet wide one-time inspection of the pressure regulator sensors and to study the maintenance plan for loss of both air bleed systems to prevent the reoccurrence of ‘loss of both air bleed systems’. To set up procedures for disabling CVR such that maintenance personnel may refer to and follow when it is required. To adopt relevant measures and trainings to ensure those maintenance personnel take appropriate manuals as the reference to fill in the maintenance log book. To have an overall review to the policies, operation procedures, trainings and the internal control mechanism of each aircraft type and the relevant personnel concerning the preservation of FDR’s evidence when a flight safety event occurs, to prevent FDR’s data from being overwritten and to handle the case by replacing a FDR as far as possible. To request cabin crew communicate the information of aircraft’s abnormal status in a speedy and effective way when an abnormal event occurs to ensure cabin safety. Six recommendations are issued to the Civil Aeronautics Administration, Ministry of Transportation and Communications. To supervise EVA Air to mandate pilots to request for emergency descent or to declare promptly the emergency situation to ATC when they encounter cabin de-pressurization and have to have emergency descent, so that the most prioritized assistance may be acquired. To supervise that the A330 aircraft type perform a fleet wide one-time inspection of the pressure regulator sensors and to study all maintenance procedures for loss of both air bleed systems to prevent any reoccurrence of ‘loss of both air bleed systems’. To supervise to set up procedures for disabling CVR such that  maintenance personnel may follow when it is required. To supervise EVA Air to have an overall review and to improve the policies, operation procedures, trainings and the internal control mechanism concerning the preservation of FDR’s evidence so that they may prevent the repeated cases of FDR data being overwritten and to handle the case by replacing a FDR as far as possible. To promote the regulations of Aviation Operation Management Regulations Article 111 related to the Airbus A330 FDR and MEL to each governed airlines to prevent the occurrence of the similar case. One recommendation is issued to Airbus. The occurrence aircraft had the incident due to the installations of the P/N ZRA380-00 pressure sensor manufactured by Auxitrol in the GE engine pylons. “Airbus” should promptly find a solution and communicate the information in a technical document more in detail than ‘Technical Follow Up’ to the operators of the A330 aircraft type for their maintenance reference.

The full investigation report in Chinese is available for download at http://www.asc.gov.tw

Sherry Liu, Engineer
Tel: 89127388-330  Email:sherry@asc.gov.tw