SYNOPSIS
During climb out from Paris Charles De Gaulle Airport (LFPG), France, on a scheduled passenger flight to Newcastle (EGNT), United Kingdom, the Flight Crew noticed that the cabin rate of climb and cabin altitude had increased rapidly, and that a white PRESSN advisory light (pressurisation fault) had illuminated on the Central Warning Panel (CWP). This was followed by a pressurisation system caution light (pressurisation failure). As the Flight Crew were completing the abnormal operation checklist, a CABIN HI ALT (cabin high altitude) warning was generated. This resulted in the Flight Crew declaring an emergency (Mayday) to Air Traffic Control (ATC), donning their oxygen masks and performing an emergency descent. During completion of the cabin high altitude checklist, they discovered that a ram air switch on the overhead panel, which controls the position of the ram air valve, was in the OPEN position instead of the normal SHUT position. The Flight Crew moved the switch to the SHUT position, which closed the ram air valve and restored normal system operation. The flight was continued to EGNT without further incident.
It was subsequently found that a non-return valve in the aircraft’s ram air system had been installed the wrong way round. This incorrectly installed valve, in combination with the ram air valve being in the open position on the occurrence flight, prevented the aircraft from pressurising correctly.
Four safety recommendations are issued as a result of this investigation.
