What happened
On February 28, 2014, an A320-232, registration PT-MZX, operated by TAM Airlines, was performing a scheduled flight from Salvador to Rio de Janeiro. The aircraft was carrying 149 passengers and 6 crewmembers. During the descent phase, while crossing FL200, the aircraft experienced a failure in the pressurization system. This malfunction triggered the automatic deployment of oxygen masks for the occupants, necessitating an emergency descent.
Despite the loss of cabin pressure, the crew managed the situation effectively, and the aircraft landed safely at Antônio Carlos Jobim International Aerodrome without further incident. There were no injuries to the 155 people on board, and the aircraft sustained no damage.
The investigation
CENIPA's investigation focused on the cause of the depressurization and the crew's response to the ventilation system fault. Investigators examined the Skin Air Outlet Valve and found that a small flap did not close completely when the valve was electrically activated, though it functioned correctly under manual activation.
Because the aircraft remained energized after landing, the Cockpit Voice Recorder (CVR) data for the period of the incident was unavailable. However, data from the Post Flight Report (PFR) allowed investigators to reconstruct the sequence of events. The investigation looked into whether the depressurization was caused by a mechanical failure in the pressurable system or by the crew's manual intervention during the execution of emergency checklists.
Findings
- Checklist interpretation: The crew was performing the procedure for a "VENT SKIN VALVE FAULT." The investigation suggests the crew may have moved the cabin pressure mode selector to manual and the manual vertical speed control to full up before reaching the required altitude of FL100/MEA. This action likely caused the outflow valve to open fully, leading to the cabin depressurization.
- Checklist ambiguity: The existing checklist did not sufficiently emphasize that the crew should reach FL100/MEA before performing the specific manual valve adjustments, potentially leading to the unintended loss of pressure.
- Component malfunction: While tests were inconclusive regarding the exact cause of the pressure loss, a gap was identified in the Skin Air Outlet Valve flap during electrical activation. Investigators could not rule out intermittent failures in the pressurization system components due to improper handling, storage, or maintenance.
Safety action
Following the investigation, safety recommendations were issued to the Brazilian National Civil Aviation Agency (ANAC) to monitor A320 pressurization system failures and to work with the manufacturer to ensure that checklist wording is clear, specifically regarding the timing of manual pressure mode selections. Additionally, the operator implemented an Engineering Order to update the Avionics Equipment Ventilation Computer (AEVC) software across its A320 fleet.