On 19 July 2011, a Virgin Australia operated Boeing Company 737-81D aircraft, registered VH-YFE, departed Brisbane on a scheduled passenger service to Mackay, Queensland. The First Officer (FO) was designated as the pilot flying for the flight.
While conducting a high speed descent into Mackay, the aircraft became low on profile and descended below the 8,500 ft lower limit of the control area (CTA) step. The aircraft departed Class C and entered Class G airspace for 2.9 NM and 32 seconds, before re-entering Class C. A clearance to depart, or re-enter Class C airspace was not obtained from ATC.
The Captain realised that they were low on profile and advised the FO, who reduced the aircraft's rate of descent. The flight continued without further incident. No other aircraft were affected during the event.
The operator conducted an investigation and determined that the crew's situation awareness of the aircraft's descent profile and proximity to the CTA steps had reduced.
This incident highlights the effect reduced situation awareness can have on aircraft operations and the importance of using all available resources, including instruments and charts, to assist with monitoring the descent profile.