What happened
A flight intended for IFR training from Archerfield to Rockhampton, carrying a flight instructor and a pilot-under-training, departed later than originally scheduled. Although the flight plan specified a 1730 departure, the aircraft actually took off seven minutes after this time. During taxiing, Air Traffic Control (ATC) questioned the pilot regarding whether the departure would occur before last light.
Despite this prompt to reconsider their plan, the crew chose to proceed with a VFR Northern departure at 1,000 ft. This maneuver moved the aircraft out of the protected circling area and into the 10 NM minimum sector altitude of 2,900 ft. Because lift-off occurred only two minutes before last light, the aircraft was operating below the required minimum altitude once night fell. This discrepancy triggered a terrain alert from ATC.
The investigation
The investigation focused on the decision-making process regarding the departure method and the timing of the flight. Investigators examined why the instructor opted for a VFR departure despite the IFR flight plan, noting the instructor's belief that a visual departure was preferred for Brisbane ATC traffic management. The investigation also reviewed the impact of the delayed departure time on the aircraft's altitude requirements relative to the onset of darkness.