Summary
On May 11, 2006, Korean Air Flight KE0691, an Airbus A300-B4-622R with registration HL-7297, experienced a loss of cabin pressure while cruising at Flight Level 320, approximately 30 nautical miles south of waypoint SALMI on route B-576 in the Taipei Flight Information Region. The aircraft had departed from Incheon International Airport, Republic of Korea, en route to Chiang Kai Shek International Airport, Taipei, Taiwan, with 128 occupants on board. The flight crew initiated an emergency descent in accordance with the Quick Reference Handbook. During the descent, 230 of 267 passenger oxygen masks deployed automatically. The aircraft leveled off at 10,000 feet, and cabin pressure was restored after the crew reset the system. The aircraft landed safely, and no damage or injuries were reported.
Aircraft and Crew
The aircraft was an Airbus A300-B4-622R. The flight crew consisted of two pilots, both properly certified and qualified under Korean Civil Aviation Regulations. No evidence indicated any physical or psychological issues, nor use of alcohol or drugs. The aircraft was within allowable weight and balance limits. Weather conditions at the time were not adverse.
Sequence of Events
At approximately 02:17 UTC, the crew encountered a loss of cabin pressure. The forward outflow valve had failed due to a broken flange in the automatic mode motor drive component. This failure prevented both automatic modes from controlling the valve, leading to the cabin pressure loss. The crew did not use manual mode to control pressure. During the emergency descent, the crew did not initiate a turn as required by standard procedure.
Investigation Findings
The investigation identified three findings related to probable causes: (1) a broken flange in the automatic mode motor drive component caused the forward outflow valve to fail and the subsequent failure of both auto modes; (2) the flight crew did not apply manual mode to control cabin pressure; and (3) no integrated procedures existed for when both cabin pressure regulators fail and rapid decompression occurs, whether to complete the "CABIN PRESS REG FAULT" procedure or proceed directly to "EMERGENCY DESCENT." Additional findings highlighted risk factors, such as the flight crew not following standard turn initiation during emergency descent. Other findings noted proper crew certification, no adverse weather, and no evidence of impairment.
Probable Cause
The probable cause was a broken flange in the automatic mode motor drive component, which rendered the forward outflow valve inoperative in both auto modes, leading to cabin pressure loss. Contributing factors were the flight crew's failure to use manual mode and the absence of integrated procedures for dual cabin pressure regulator failure with rapid decompression.
Safety Recommendations
The Aviation Safety Council issued safety recommendations to Korean Air to ensure flight crew adherence to emergency procedures and to review and integrate related emergency procedures for loss of cabin pressure. Recommendations also went to the Korean Ministry of Construction & Transportation to monitor Korean Air's implementation, and to Liebherr-Aerospace/France to conduct more detailed exploration of the damaged flange.