What happened
On April 6, 2018, a Boeing 737-8EH, registration PR-GGE, operated by GOL Airlines, was climbing through flight level 25,000 feet when a cabin altitude alert sounded. The alert indicated that the internal atmospheric pressure had dropped to levels equivalent to an altitude of 10,000 feet.
In response to the depressurization, the crew initiated an emergency descent. During the descent, the passenger cabin oxygen masks deployed automatically. The crew managed to stabilize the aircraft by descending to 10,000 feet, after which the flight continued to its destination at a lower altitude. The aircraft landed safely without further issues, and all 167 passengers and 6 crewmembers remained unharmed. The aircraft sustained no damage.
The investigation
CENIPA's investigation revealed that the incident was caused by an incorrect configuration of the aircraft's pressurization and air-conditioning systems. The aircraft had been dispatched with Bleed 1 inoperative, according to the Minimum Equipment List (MEL). During the flight, the crew configured the system in a manner that prevented Pack 1 from receiving necessary bleed air, leading to a slow, progressive depressurization.
The investigation found that the crew's performance was impacted by several factors. The commander, acting as the Pilot Flying, took the initiative to configure the pressurization panel from memory rather than consulting the MEL, which was a task typically assigned to the Pilot Monitoring. This led to a lack of effective task division and prevented the crew from identifying the error in real time. Additionally, the investigation noted that some oxygen masks in the passenger cabin, including one in a lavatory and several in specific seat rows, failed to deploy correctly from their compartments.
Findings
- Improper system configuration of the bleed air and isolation valves prevented effective cabin pressurization.
- Inadequate Crew Resource Management (CRM), characterized by a lack of effective communication and a failure to maintain proper division of tasks between the pilots.
- Non-observance of procedures, as the commander performed system configurations from memory instead of utilizing the MEL.
- Incomplete checklist execution, as the crew did not perform all required actions from the Quick Reference Handbook (QRH) following the depressurization.
- Equipment malfunction, specifically the failure of certain oxygen mask compartments to open during the altitude drop.