On 12 July 2018, a Boeing 737-800 was climbing through FL135 soon after takeoff from Sydney with First Officer line training in progress when the cabin altitude warning horn sounded because both air conditioning packs had not been switched on. The Captain took control and descended the aircraft to FL100 until the situation had been normalised and the intended flight was completed. The Investigation noted that although both pilots were experienced in command on other aircraft types, both had limited time on the 737 and concluded that incorrect system configuration was consequent on procedures and checklists not being managed appropriately.