Tigerair Australia flight TT229 was a flight operated with Boeing Company 737-8FE, VH-VUB on 12 July 2018 from Sydney, New South Wales to Melbourne, Victoria.

For this flight, a trainee First Officer was the pilot flying (PF) and a training Captain was the pilot monitoring (PM).

The pilots switched off both air conditioning packs in accordance with the standard operating procedure (SOP) for starting the engines.

The before taxi procedure followed engine start and although it included selecting the air conditioning packs to AUTO, the air conditioning packs remained OFF.

The aircraft took off at about 1136 Eastern Standard Time (EST).

After flap retraction at approximately 1137, the crew completed the final component of the take-off procedure, followed by the after take-off checklist.

At about the same time, air traffic control (ATC) issued several instructions to the crew of Tigerair Australia flight TT229

Tigerair Australia flight TT229

The take-off procedure and after take-off checklist both included a requirement to check the position of the air conditioning packs switches.

However, during both the procedure and the checklist, the packs were not identified as being OFF.

At about 1142, while the aircraft was still climbing and passing 13,500 ft, the cabin altitude warning horn sounded.

The First Officer identified that both air conditioning packs switches were in the OFF position.

Both packs were then immediately switched to AUTO. The Captain took over control of the aircraft and selected altitude hold on the autopilot.

The aircraft reached a maximum height of 14,900 ft (at about 1144), whereby the Captain disengaged the autopilot and commenced a descent to 10,000 ft.

The warning ceased at about 1146.

During this time, both pilots donned oxygen masks in accordance with the cabin altitude warning procedure.

Once level at 10,000 ft, the crew completed the remainder of the cabin altitude warning checklist.

As the cabin pressure was now under control and operations were normal, the crew continued the flight to Melbourne.

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From the evidence available, the following findings are made with respect to the incorrect configuration of a Boeing Company 737-8FE, registered VH-VUB, that occurred near Sydney, New South Wales on 12 July 2018.

These findings should not be read as apportioning blame or liability to any particular organisation or individual.

Contributing factors :

• The aircraft did not pressurise due to an incorrectly configured pressurisation system.
• The incorrect configuration was the result of procedures and checklists not being managed appropriately