B738, en-route, near Lugano Switzerland, 2012

B738, en-route, near Lugano Switzerland, 2012

Summary

On 4 April 2012, the cabin pressurisation controller (CPC) on a Boeing 737-800 failed during the climb passing FL305 and automatic transfer to the alternate CPC was followed by a loss of cabin pressure control and rapid depressurisation because it had been inadvertently installed with the shipping plug fitted. An emergency descent and diversion followed. The subsequent Investigation attributed the failure to remove the shipping plug to procedural human error and the poor visibility of the installed plug. It was also found that the pressurisation system ground test after CPC installation was not suitable to detect the error.

Description

On 4 April 2012, a Boeing 737-800 (MSN 33546) being operated by an Irish carrier on a scheduled passenger flight from Bergamo to East Midlands and in the climb approaching FL310 in day Visual Meteorological Conditions (VMC) declared a MAYDAY and made an emergency descent after loss of pressurisation control occurred before making an en route diversion to Frankfurt Hahn without further event. Some minor passenger injuries attributable to the sudden pressure changes were reported.

Investigation The Swiss Accident Investigation Board delegated the Investigation to the German Federal Bureau of Aircraft Accident Investigation (Bundesstelle für Flugunfalluntersuchung (Germany) (BFU)). Data from the SSFDR and the SSVCR were successfully downloaded, as were Non Volatile Memory data from the Cabin Pressure Controllers. Relevant ATC radar recordings were also available. The flight crew consisted of a Commander with 5800 hours of his 6000 total flying hours on type and a First Officer with 120 hours of his 820 total flying hours on type.

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