Departure Decision
The flight was planned as an IFR training flight from Archerfield to Rockhampton, with a flight instructor and a pilot-under-training on board. Despite the IFR flight plan, the instructor chose to conduct the VFR Northern departure instead of an IFR departure. The instructor believed that the VFR Northern departure was the preferred method for Brisbane air traffic control (ATC) traffic management.
Timing and ATC Query
While it was feasible that the aircraft would reach the required minimum altitude before last light based on the flight plan departure time of 1730, take-off actually occurred 7 minutes later than planned. As the aircraft was taxiing for departure, ATC queried the pilot, who was making the radio calls, regarding whether they would depart before last light. This query provided a prompt for the instructor and pilot to reconsider their plan. However, they elected to continue with the VFR Northern departure at 1,000 ft.
Terrain Alert
The VFR Northern departure took the aircraft out of the circling area and into the 10 NM minimum sector altitude of 2,900 ft. Lift-off occurred 2 minutes prior to last light. Consequently, after last light, the aircraft was below the 10 NM minimum altitude and outside the circling area, which triggered a terrain alert from ATC.