What happened
Following the conclusion of hoist training exercises near Golden Beach, Victoria, an AW139 operated by Esso Australia encountered unexpected fog. The instructor pilot decided to climb to clear the fog, heading northwest toward the shoreline. At the time of the departure, the aircraft was still in a hoisting configuration, with the main cabin door locked open and the hoist extended approximately 40 feet below the helicopter. Additionally, the main rotor RPM was set to 102%.
As the aircraft climbed, it transitioned from visual meteorological conditions into instrument meteorological conditions. This loss of external visual references caused the instructor to experience spatial disorientation. Flight data indicates that the pilot's control inputs became uncertain, leading to a nose-down attitude and an increase in airspeed beyond 80 knots. This unstable flight state triggered an enhanced ground proximity warning system (EGPWS) alert as the aircraft descended below 150 feet.
The investigation
The investigation examined the crew's transition from visual to instrument conditions and the aircraft's configuration during the event. It was found that the instructor initiated the climb before the post-hoist procedures were completed. These procedures are designed to secure the cabin, stow the hoist, and adjust the rotor RPM to 100% once the aircraft accelerates.
Furthermore, the captain, acting as the pilot monitoring, was distracted by recording a GPS position in the flight management system. Because the captain was focused on this task, they did not observe the transition into the fog and were unaware of the instructor's immediate intention to depart. When the terrain alert sounded, the captain reactively took control of the aircraft, which created a risk of control conflict between the two crew members.
Findings
- The instructor initiated a hasty departure to avoid fog before the hoist was secured and the cabin door was closed.
- The pilot flying experienced spatial disorientation after entering instrument meteorological conditions.
- The aircraft's configuration, including the extended hoist and open door, led to airspeed exceedances while the rotor RPM was at 102%.
- The pilot monitoring was distracted by administrative tasks, reducing situational awareness regarding the aircraft's flight path.
- The operator lacked specific procedures for recovering an aircraft from inadvertent IMC during hoist operations or managing EGPWS alerts in this specific configuration.