What happened
On 4 November 2023, a Gulfstream 695A, registration VH-HPY, was performing an instrument flight rules mission from Toowoomba to Mount Isa, Queensland. The flight, operated by AGAIR, was intended for aerial line scanning of fire zones. The aircraft was carrying the pilot and two camera operators.
During the cruise phase at flight level 280, approximately one hour and 50 minutes into the flight, air traffic control lost radio communication with the aircraft. After observing the plane deviate from its assigned track, controllers initiated an uncertainty phase. During this period, controllers reached the pilot via a mobile telephone; however, the pilot's speech was noted as being unusually slow and flat. This prompted controllers to upgrade the situation to an alert phase and begin hypoxia emergency protocols.
Although direct radio contact was eventually re-established, the pilot's communication quality continued to decline. The pilot's speech became increasingly slow, quiet, and characterized by stuttering and operational errors. Following a period of silence lasting approximately 18 minutes, the aircraft left controlled flight. The aircraft entered an anticlockwise descent and transitioned into an aerodynamic spin at roughly 10,500 feet, descending at an average rate of 13,500 feet per minute. The aircraft struck terrain 55 km southeast of Cloncurry. The impact and subsequent fire caused the 3 fatalities on board and the total destruction of the aircraft.
Findings
Radio communications indicated a progressive decline in the pilot's cognitive and physical state, marked by a significant reduction in speech volume and rate, as well as increased difficulty in repeating clearances.