Eva Air A332 near Simferopol on Dec 29th 2010, loss of cabin pressure

Last Update: April 23, 2012 / 14:49:33 GMT/Zulu time

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Incident Facts

Date of incident
Dec 29, 2010

Cause
Loss of cabin pressure

Airline
Eva Air

Aircraft Type
Airbus A330-200

ICAO Type Designator
A332

Taiwan's Aviation Safety Council (ASC) released their final report in Chinese concluding the probable cause of the incident were:

The pressure sensors of the engine #1 and engine #2 bleed pressure regulator systems were exposed to condensed water due to ambient temperature changes. When the aircraft was enroute in temperatures below zero degrees Centigrade, the condensed water in the pressure sensors iced up in succession resulting in erroneous pressure indications, the regulator computer therefore closed the pressure regulating valves.

When the cabin altitude warning appeared and the relevant checklist required a descent, the crew requested a descent but did not declare emergency or initiate an emergency descent. The unaware controller did therefore not provide priority and cleared the aircraft only for a descent to FL280.

The captain and aircraft commander (52, ATPL, 12,152 hours total, 4,781 hours on type) was taking his planned rest, the first officer (37, ATPL, 5,268 hours total, 2,137 hours on type) was pilot flying from the right hand seat, a second captain (40, ATPL, 12,419 hours total, 4,929 hours on type) was pilot monitoring occupying the left hand seat, when the crew received "AIR ENG 1 BLEED FAULT" and "AIR ABNORM BLEED CONFIG" messages. The crew worked the checklists and attempted to reset the pressure control system twice without success. As the checklists did not recommend any further action the crew did not notify the commander and continued the flight at FL400.

26 minutes later the second captain left the cockpit for a toilet break, the first officer remained on the flight deck alone, when a "AIR ENG 2 BLEED FAULT" message appeared and the cabin pressure began to rise. The first officer attempted to reset the system one time without success and requested a descent about one minute later. Ukraine's ATC cleared the aircraft to descend to FL360. ATC inquired whether the flight would declare emergency, the first officer replied negative.

The second captain, while still in the lavatory, felt the rising cabin pressure via his ears and immediately returned to the cockpit.

Two minutes after the second bleed fault message the ECAM displayed "CAB PR EXCESS", the aircraft was just descending through FL370 and the cabin altitude climbed through 9500 feet. Both second captain and first officer donned their oxygen masks. The second captain subsequently requested a descent to 10,000 feet. The air traffic controller, unaware of the developing situation on board, considered conflicting traffic and cleared the flight to descend to FL280. The second captain now requested the purser to notify the commander, who in turn arrived at the cockpit when the aircraft descended through FL320 and the cabin altitude climbed through 11,000 feet and took the observed seat. Just before levelling off at FL280 the crew received a TCAS traffic advisory. While level at FL280 the commander considered that he could not estimate how long the conflict with other traffic would persist, the passenger oxygen masks would be automatically released at 14,000 feet and decided to manually release the passenger oxygen masks and to request vectors from ATC for further descent.

6 minutes after the second bleed fault message the crew managed to reset one of the bleed air systems, the cabin altitude reached a peak of 12,352 feet and began to decrease again, when air traffic control cleared the flight down to 10,000 feet. 2 minutes later, the aircraft descended to FL160 with the cabin altitude still above 11,000 feet, the crew requested further descent to 8000 feet. After levelling off at 8000 feet the cabin altitude excess indication extinguished. The commander and second captain changed place, the commander took control of the aircraft and the first officer assumed role of pilot monitoring. The commander assessed that the aircraft was unable to continue to destination and decided to divert to Simferopol for a safe automatic landing. There were no injuries.

According to the quick access recorders the ambient outside air temperature at FL400 had been between -72 and -70 degrees Centigrade over a period of 65 minutes prior to the first bleed fault. Following the first bleed fault the ambient outside air temperature rose to about -64 degrees C for about 30 minutes.

The ASC mentioned the cockpit voice recordings were not available for the investigation as the cockpit voice recorder had not been deactivated/preserved after landing.

The ASC analysed that the actions to request descend following the onset of the second bleed fault were justifyable in order to attempt reset of the system. However, when the cabin pressure warning appeared upon descending through FL370 and emergency descent was required, the crew however only requested a descent to 10,000 feet without explanation to air traffic control, did not declare emergency and did not initiate an emergency descent. ATC could clear the flight only to FL280 due to traffic at FL270, and not being aware of the urgency on board of flight BR-61 did not issue vectors to the conflicting traffic to move that traffic out of the way of BR-61 and free the flight path for an emergency descent. BR-61 therefore had to level off at FL280 until clear of conflict.

The ASC analysed that oxygen supply available for passengers and crew should last at least 10 minutes for flight above FL250, the flight manual states an average value of 5 minutes for descent from FL400 to FL100 with a rate of descent of 6000 feet per minute. With the intermediate level off at FL280 the descent from FL360 to FL100 actually took 8 minutes 25 seconds.

The flight data and quick access recorders showed the pressure sensors, just prior to their respective faults, indicated 60 pounds per square inch over a period of 15 seconds causing the pressure controller to close the attached bleed air regulating valve resulting in a dual system failure. Post flight examination of the pressure sensors after dismantling the sensors showed water inside the sensors, which had condensed as result of operating in tropic climate highly humid air had been processed by the engine compressors. During expansion of that highly compressed moist air in the bleed air system that humidity condenses in the pipes. That condensed water ingressed the pressure sensors, one side of which is encapsulated with a metal film and the other with silicone. When enroute that water ingress was exposed to less than zero degrees Centigrade that water iced up expanding and filling all room for the measurement unit to move and created an indication of too high a pressure. The actual ambient temperature of -70 to -72 degrees Centigrade was lower than the certified minimum temperature of -64 degrees Centigrade permitting the temperatures around the probes to drop to zero degrees Centigrade or lower.

The investigation released safety recommendations to the operator including requiring crew to declare emergency in case of loss of cabin pressure, to develop a procedure for dual system failure of engine supplies and to ensure black box recordings are being preserved, to the Civil Aviation Authority to ensure the operator requires crew to declare emergency in case of loss of cabin pressure, develop a procedure to avoid another dual failure of engine supply systems, and to the aircraft manufacturer to improve design of the probes. As a safety action Airbus had already released a service bulletin in September 2011, that had recommended to replace at least the #1 regulator pressure sensor to a new model in order to reduce the risk of a dual failure, the new model having introduced the possibility to drain water ingress.
Incident Facts

Date of incident
Dec 29, 2010

Cause
Loss of cabin pressure

Airline
Eva Air

Aircraft Type
Airbus A330-200

ICAO Type Designator
A332

This article is published under license from Avherald.com. © of text by Avherald.com.
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