Description

On 12 July 2018, a Boeing 737-800 (VH-VUB) being operated by Tiger Airways on a scheduled domestic passenger flight from Sydney to Melbourne during daylight hours on a line training flight for the First Officer was passing FL 135 in the climb approximately 6 minutes after takeoff when the cabin altitude warning horn sounded. The trainee First Officer immediately recognised that both air conditioning packs were switched off and selected them to on and the Captain took control and descended the aircraft to FL100 until pressurisation was normalised after which the flight was completed without further event.

Investigation

An Investigation was carried out by the Australian Transport Safety Bureau (ATSB). Data were retrieved from both the FDR and CVR but only that from the former was analysed. These data confirmed that although both engine bleed switches had been ‘on’ from takeoff, both air conditioning packs had been ‘off’ throughout that time. FDR parameters did not include cabin altitude but it was considered that since the cabin oxygen masks had not automatically deployed, it was unlikely to have exceeded 14,000 feet.