What happened
On 1 February 2025, a Sikorsky S-92A helicopter, registered VH-IPE, was performing a night recency flight toward an offshore drilling rig north-north-west of Exmouth, Western Australia. While descending toward the rig, the pilot flying attempted to adjust the aircraft's heading to avoid flying directly over the structure. During this process, the pilot accidentally pressed the vertical speed key instead of the intended heading hold mode. This error went unnoticed by the crew and resulted in the cancellation of an automation mode designed to level the aircraft at a preset circuit height. Consequently, the helicopter maintained a descent rate of 500 feet per minute, continuing downward until an enhanced ground proximity warning system (EGPWS) alert triggered at approximately 220 ft.
The investigation
The ATSB examined the cockpit environment and the experience levels of the crew. The investigation found that the flight crew had limited experience flying the Sikorsky S-92A at night. The pilot monitoring had only approximately 9 hours of night experience on the type, while the pilot flying had only 13 hours of night experience in simulators and training. The investigation also noted that the flight was shorter than usual, which reduced the time available for cockpit administration and increased the workload. The physical layout of the autopilot panel contributed to the error, as the heading and vertical speed keys are positioned closely together and were not backlit while the mode was inactive, making them difficult to distinguish in the dark cockpit.
Findings
- The crew was experiencing a high workload due to a shorter-than-normal flight sector.
- An inadvertent autopilot mode selection error cancelled the automated leveling function.
- The pilot flying's request for the pilot monitoring to recalculate the take-off safety speed (Vtoss) diverted attention away from altitude monitoring.
- The crew failed to identify that the aircraft had not leveled off at the 660 ft circuit height.
- The operator's operational risk assessment failed to account for the risks associated with the crew's limited night experience on this specific aircraft type.