What happened
During a flight near RAAF Base Amber andley, a pilot operating a hot air balloon under visual flight rules (VFR) encountered localized fog. Although the initial weather forecast indicated only a 30% chance of fog with 500 m visibility, and no fog was present during pre-flight preparations, the pilot encountered a fog patch to the southeast of the base during the flight.
As the pilot began descending to find a landing site, a change in wind direction caused the balloon to drift toward the fog. Rather than staying above the fog layer to maintain clear air, the pilot continued the descent into the obscured area, expecting sufficient visibility for landing. Once inside the fog, visibility dropped to just 10 m. During this period, the pilot spotted a tree. An attempt to climb by lighting the burners was initiated, but the insufficient time required to arrest the descent and begin a climb meant the collision could not be avoided. The impact caused damage to the balloon's envelope.
The investigation
The investigation focused on the pilot's decision-making regarding visibility and the physical limitations of the aircraft. While the flight took place in Class G airspace, the proximity to the RAAF Base's instrument approach procedures required the balloon to remain clear of clouds and maintain at least 5,000 m of visibility. The investigation determined that even if the regulatory visibility requirements had been lower, the balloon's performance characteristics would have likely resulted in the same collision due to the delay in climb initiation.
Findings
- The pilot entered a patch of fog that violated the visibility requirements for VFR flight.
- The reduction in visibility to 10 m prevented the pilot from identifying and avoiding the obstacle in time.
- The collision resulted in damage to the balloon's envelope.