What happened
On December 6, 2019, a Boeing 737-401, registration YV3011, operated by Avior Airlines C.A., experienced a sudden loss of cabin pressure while cruising at FL330. The aircraft was flying a direct route from Salinas to Tarapoto, Peru, deviating from its original flight plan to Caracas, Venezuela.
Following the depressurization, the flight crew initiated an emergency descent. They initially descended to FL190 to maintain safety above the Andes Mountains, and subsequently to FL110. During the descent, the aircraft's oxygen masks deployed; however, the crew encountered difficulties with the use of the masks. Due to the failure of some passengers to properly activate their masks, an infant passenger suffered a medical emergency (decompensation). Consequently, the captain diverted the flight to the nearest alternate airport, Tarapoto, to ensure medical assistance was available.
The investigation
The investigation conducted by the CIAA focused on the mechanical cause of the pressure loss and the subsequent emergency procedures. Investigators examined the aircraft's pressurization system, including the outflow and safety relief valves. The investigation also reviewed maintenance records, crew training, and the operational circumstances regarding the flight plan deviation and oxygen supply limitations.
Findings
- The investigation established that unsecured isolation blanket material located in the aircraft's tail compartment had shifted. This material obstructed the operation of both the outflow valves and the safety relief valves, leading to the sudden and uncontrolled loss of cabin pressure.
- A contributing factor was the lack of specific procedures for inspecting the tail compartment during anti-drug searches, which may have resulted in the failure to properly secure the insulation blankets according to the manufacturer's technical documentation.
- The flight was operating with oxygen generators providing only 12 minutes of supply, and the deviation from the original flight plan, combined with the emergency descent requirements, placed the crew in a high-pressure situation regarding oxygen availability.