An instructor pilot became spatially disorientated when their AW139 helicopter inadvertently entered fog during a winch training exercise, resulting in a ground proximity alert where the helicopter descended below 150 ft above sea level, an ATSB investigation details.
On 2 August 2024, the Esso Australia operated twin-engine offshore industry support helicopter was conducting hoisting training just off the coast near Golden Beach, in Victoria's Gippsland region, operating under visual flight rules.
On board were a captain, a flight instructor, a check aircrewman, and a hoist operator. The exercise, with the captain as the pilot flying, involved retrieving a training aid amidst large swells, sea spray and encroaching fog.
"During the 40‑minute training exercise, the gap between the helicopter and the fog diminished," ATSB Director Transport Safety Dr Stuart Godley said.
At the conclusion of the exercise, the instructor took over as pilot flying, and the crew began to recover the training aid, but were initially unsuccessful.
"Observing the encroaching fog, the instructor immediately elected to depart and announced they would climb to avoid the fog," Dr Godley continued.
"The hasty departure from the training area occurred before the hoist was secured, with the door open, and while the captain (now pilot monitoring) was still occupied with recording the training aid position."
The helicopter then inadvertently entered the fog - instrument meteorological conditions, or IMC - and the instructor became spatially disoriented.
"The instructor's attempt to exit IMC while spatially disoriented resulted in control inputs that led to the helicopter entering an unstable state while still in IMC, triggering a terrain alert below 150 ft, and maximum airspeed exceedances for operations with the door open and the hoist extended," Dr Godley said.
The captain then took back control of the helicopter from the instructor, and initiated a climb, exiting IMC and continuing the flight without further incident.
"This serious incident highlights just how loss of visual references for a pilot operating under visual flight rules can lead to spatial disorientation, reduced situational awareness and a loss of control," Dr Godley said.
"As such, it highlights the importance of pilots proactively managing the risks of inadvertent entry into IMC."
While it did not contribute to this serious incident, the ATSB's investigation also found Esso Australia did not have a procedure for helicopter recovery from inadvertent IMC during hoist operations, or recovery procedures for terrain alerts or advisories.
In response, the operator has conducted an internal investigation, and identified several actions to be taken.
"This serious incident shows the importance of establishing and monitoring operational safety margins, adherence to documented procedures, maintaining situational awareness and fostering effective crew resource management during high‑workload scenarios like hoisting and search and rescue operations," Dr Godley concluded.
"The challenges presented by degraded visual environments, such as inadvertent entry to instrument meteorological conditions, increase the likelihood of spatial disorientation and loss of control in flight."
You can find here the final report: Loss of control in flight involving Leonardo Helicopters AW139, VH-EXK, 19 km east of Longford Heliport, Victoria, on 2 August 2024
