What happened
While climbing toward its assigned cruising altitude, the aircraft experienced a sudden loss of cabin pressure. This rapid depressurisation was triggered by a malfunction in the forward outflow valve, which prevented the system from maintaining the required pressure levels. Upon noticing that the cabin pressure warning system had activated at approximately 12,600 ft, the flight crew immediately donned their oxygen masks.
The investigation
The investigation focused on the mechanical failure of the pressurisation system and the subsequent communication challenges during the emergency. It was determined that the forward outflow valve was not functioning correctly, which directly caused the loss of pressure. Additionally, investigators examined the effectiveness of the emergency procedures and crew communication during the descent.
Findings
- The primary cause of the depressurisation was the malfunctioning forward outflow valve.
- The captain's emergency announcement over the passenger address (PA) system was muffled, likely due to the crew wearing oxygen masks.
- Because the announcement was difficult to hear, the cabin crewmember did not immediately recognise that an emergency descent was underway or that supplemental oxygen was required.