What happened
A private flight was planned from a departure landing area to Charters Towers and Atherton. During the flight, the pilot encountered rising terrain and low cloud heights while attempting to navigate around weather. After determining that the original route was unsuitable, the pilot diverted toward Mareeba, tracking north along the Kennedy Developmental Road. As the terrain elevation increased, the aircraft was unable to maintain the required 500 ft terrain clearance or the necessary visibility, resulting in the aircraft entering instrument meteorological conditions (IMC).
Upon entering the cloud, the pilot experienced a sudden "white-out" and attempted to avoid the cloud by reducing power and initiating a left turn. This led to severe spatial disorientation, characterized by rapid altitude fluctuations. In an attempt to stabilize the aircraft, the pilot engaged the autopilot. However, because the aircraft was already in a climb and power was reduced, the autopilot maintained a high rate of climb that caused the airspeed to decay. The aircraft's airspeed likely fell below its stall speed, leading to a stall and a rapid loss of altitude. During the subsequent descent, the aircraft struck trees but remained airborne.
The investigation
The investigation focused on the pilot's pre-flight planning and in-flight decision-making. It was determined that while the pilot had checked weather for the destination, they failed to obtain necessary forecasts for the intended flight path. This lack of information meant the pilot was unaware that cloud bases along the route were lower than the surrounding terrain elevations. The investigation also examined the aircraft's flight path, noting that the pilot continued toward the destination despite being unable to maintain safe terrain clearance, which increased the risk of entering IMC.
Findings
- The pilot's pre-flight planning was inadequate regarding the planned altitude and weather conditions en route.
- The pilot continued flight toward the destination despite being unable to maintain the minimum 500 ft terrain clearance.
- The pilot entered IMC at a low altitude and reduced power while experiencing spatial disorientation.
- The engagement of the autopilot at reduced power during a climb caused the airspeed to drop below the stall speed.
- The pilot did not divert to the nearest suitable aerodrome after the aircraft sustained damage and controllability issues, continuing for 1.5 hours to a larger airport.