What happened
On December 29, 2010, EVA Air flight BR 61, an A330-203 with registration B-16312, was operating a flight from Bangkok (BKK) to Vienna (VIE). While cruising at 40,000 feet within the Simferopol Flight Information Region (FIR), the aircraft experienced a simultaneous failure of both engine bleed air systems. This failure led to an abnormal cabin pressure situation, prompting the flight crew to initiate emergency descent procedures. The crew utilized emergency oxygen during the descent. Following guidance from air traffic control, the aircraft landed safely at Simferopol International Airport at 14:05 local time. There were no fatalities or injuries and no damage to the aircraft.
The investigation
The Taiwan Transportation Safety Board (TTSB) conducted the investigation in coordination with Ukrainian authorities, the French BEA, Airbus, and the Civil Aviation Administration of the Republic of China. The investigation focused on the technical cause of the dual bleed air loss and the crew's response to the depressurization warning. Investigators examined the pressure regulating sensors, the environmental conditions during cruise, and the maintenance records of the aircraft. The investigation also reviewed the cockpit voice recorder (CVR) handling and the effectiveness of the crew's communication with air traffic control during the emergency.
Findings
- The primary cause of the dual system failure was the accumulation of ice within the pressure regulating sensors of both engine 1 and engine 2. Due to the extremely low ambient temperatures (averaging -61°C) during cruise, condensation formed inside the sensors and subsequently froze. This ice caused the sensors to transmit erroneous high-pressure signals, leading the monitoring computer to incorrectly close the pressure regulating valves.
- The aircraft was equipped with General Electric (GE) engines; data indicated that A330 models using GE engine nacelles face a higher risk of this specific bleed air system failure compared to those using Pratt & Whitney or Rolls-Royce engines.
- During the emergency descent, the crew followed procedures following the "CAB PR EXCESS CABIN ALT" warning but did not explicitly declare an emergency or request an emergency descent to air traffic control. Consequently, they did not receive the highest priority assistance, which could have facilitated a faster descent to a safe altitude.
- Maintenance records showed the aircraft had been maintained in accordance with airworthiness requirements prior to the event.