Avior B734 near Tarapoto on Dec 6th 2019, loss of cabin pressure

Last Update: April 25, 2021 / 21:07:47 GMT/Zulu time

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Incident Facts

Date of incident
Dec 6, 2019

Classification
Incident

Flight number
9V-1521

Departure
Lima, Perú

Aircraft Registration
YV3011

Aircraft Type
Boeing 737-400

ICAO Type Designator
B734

An Avior Airlines Boeing 737-400, registration YV3011 performing flight 9V-1521 from Lima (Peru) to Caracas (Venezuela) with 133 passengers and 6 crew, was enroute at FL330 near Tarapoto (Peru) when the crew initiated an emergency descent due to the sudden loss of cabin pressure, the passenger oxygen masks were released. The aircraft stopped the descent at FL190 due to the minimum safe altitude above terrain (Andes mountains) and were later cleared to FL090 by ATC when terrain clearance was assured. The aircraft diverted to Tarapoto for a safe landing on runway 35. A baby was taken to a hospital for a precautionary check.

The airline reported all passengers are in good health. A replacement aircraft is being chartered to take the passengers to Caracas.

On Apr 25th 2021 Peru's CIAA released their final report in Spanish only (Editorial note: to serve the purpose of global prevention of the repeat of causes leading to an occurrence an additional timely release of all occurrence reports in the only world spanning aviation language English would be necessary, a Spanish only release does not achieve this purpose as set by ICAO annex 13 and just forces many aviators to waste much more time and effort each in trying to understand the circumstances leading to the occurrence. Aviators operating internationally are required to read/speak English besides their local language, investigators need to be able to read/write/speak English to communicate with their counterparts all around the globe).

The report concludes the probable cause of the serious incident were:

The outflow and safety relief valves were unable to operate due to being blocked by insulation blankets covering the walls in the tail compartment of the aircraft, the blankets became loose for unknown reasons which resulted in a sudden depressurization of the aircraft.

Contributing was that there are no procedures for repeated/continuous inspections of the tail compartment, where both valves are being installed. Short time available probably caused the non-application of the manufacturer's procedures so that the blankets were not assured to remain in place.

The CIAA reported the infant in the arm of the mother could not be supplied with oxygen during the emergency and showed signs of oxygen deprivation. The infant was taken to a hospital, where the infant was stabilized. The infact could be discharged from hospital.

The CIAA analysed that after levelling off at FL330 the air conditioning systems were working normally stabilizing the cabin pressure at the equivalent of 6400 feet MSL with a pressure differential of 6.4 psi. However, the outflow valve became obstructed by the insulation blankets which increased the cabin pressure up to a differential of 8.65 psi at which point the safety valve opened and became stuck in the open position due to the insulation blankets causing the sudden depressurization of the cabin. The crew worked the related memory items and checklists, donned their oxygen masks, released the passenger oxygen masks, and tried to control the cabin pressure manually without success. Observing the terrain minimum safe altitude the aircraft performed an emergency descent to FL190. The passenger oxygen masks needed to be used for the full time of 13 minutes, that the oxygen generators were providing.
Incident Facts

Date of incident
Dec 6, 2019

Classification
Incident

Flight number
9V-1521

Departure
Lima, Perú

Aircraft Registration
YV3011

Aircraft Type
Boeing 737-400

ICAO Type Designator
B734

This article is published under license from Avherald.com. © of text by Avherald.com.
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