What happened
While operating at approximately 900 ft AGL in 10–15 kt winds, the pilot of hot air balloon VH-FSR initiated a descent intended to reduce the aircraft's forward progress. During this maneuver, the pilot of VH-FSR identified another balloon, VH-OOP, flying roughly 1,150 m ahead at an altitude of about 100 ft AGL within a slower wind layer.
The pilot of VH-FSR incorrectly assessed that VH-OOP was flying at a higher altitude within the same faster air stream. Under the mistaken belief that sufficient separation would be maintained while moving behind the lead balloon, the pilot continued the descent. This error caused VH-FSR to converge toward the path of VH-EPO.
As the risk of impact became apparent, the pilot of VH-OOP attempted to communicate via four separate radio broadcasts. However, the pilot of VH-FSR was focused on managing the descent and failed to recognize these calls as being directed to them. Realizing a collision was unavoidable, the pilot of VH-FSR maneuvered the descent to ensure that only the envelopes made contact, specifically avoiding any basket-to-envelope impact. The pilot of VH-OOP also worked to maintain a steady altitude to assist in this mitigation. Ultimately, the collision resulted in no damage to either aircraft.
The investigation
The investigation focused on the sequence of maneuvers and the communication breakdown between the two crews. Investigators examined the atmospheric conditions, noting the presence of different wind layers that influenced the flight paths of both balloons. The inquiry also looked into the pilot's perception of the lead balloon's altitude and the failure to respond to radio transmissions during the critical phase of the descent.