Incident Overview
On February 27, 2024, a Boeing 737-800 operated by Mongolian Airlines with registration JU-1088 experienced an in-flight cabin altitude warning while en route from Hong Kong to Ulaanbaatar. The incident occurred approximately 33 minutes after takeoff, when the aircraft was climbing through flight level 348.35.
Flight Details and Response
The aircraft departed Hong Kong International Airport at 04:41:50 UTC. It reached a cruising altitude of 33,100 feet and maintained this level for 45 minutes before resuming its climb. At 34,835 feet, the "Cabin Altitude Warning Horn" activated. The flight crew reported hearing a hissing sound near door 2R and experiencing ear pain. Some passengers also reported similar symptoms, and one male passenger in seat 20 required supplemental oxygen due to feeling unwell.
Following the warning, the aircraft continued climbing for another minute and 40 seconds, reaching a peak altitude of 35,494 feet before beginning a descent. The crew utilized emergency oxygen masks as required by international regulations. The aircraft descended to 8,000 feet and landed safely at Beijing Capital International Airport (PEK) at 08:04 UTC.
Investigation and Findings
The Air Accident Investigation Bureau of Mongolia conducted the investigation under the authority of the Ministry of Road and Transport. No injuries were reported among the 10 crew members or 126 passengers, and no damage was found to the aircraft or other property. The final report, issued on April 30, 2025, focuses on determining the technical circumstances and probable causes to prevent future occurrences, in accordance with Annex 13 of the Chicago Convention.