An Esso Australia VFR AW139 descended to less than 150 feet AMSL in fog during a training exercise in Victoria last year because the instructor became disoriented, according to the ATSB.
In an investigation report published this week, the ATSB found that the instructor hastily departed the training area to avoid encountering a fog bank off Golden Beach in August 2024, but the aircraft descended to only 140 feet above the sea as the aircraft entered IMC.
On board VH-EXK 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.
After the exercise finished the instructor took over as pilot flying, but the crew were unsuccessful in recovering the training aid from the sea.
“Observing the encroaching fog, the instructor immediately elected to depart and announced they would climb to avoid the fog,” Godley said.
“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.”
EXK then entered the fog, leading to the instructor becoming spatially disoriented. During attempts to get out of the fog, the instructors made control inputs that resulted in an unstable condition, triggering a terrain alert. The aircraft also exceeded the maximum airspeed for the door open and the hoist extended.
The captain took over the aircraft and climbed to get out of the fog.
“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,” Godley said.
“As such, it highlights the importance of pilots proactively managing the risks of inadvertent entry into IMC.”
Although the ATSB did not consider it a contributing factor, investigators found that Esso Australia did not have a standard procedure for inadvertent IMC entry when the hoist was extended.
The full investigation report is on the ATSB website.