Some fire managers in the United States may assume that aerial ignition of a prescribed fire by using plastic spheres began a few decades ago and has only been carried out with helicopters, and more recently with drones. But a film produced by the Commonwealth Scientific and Industrial Research Organisation (CSIRO), an independent Australian federal government agency responsible for scientific research, documented the routine practice of aerial ignition from a fixed wing aircraft in 1971.
The concept is similar to the plastic spheres used today which are manufactured containing a chemical. The injection of a second chemical just before the capsule is jettisoned begins a reaction that results in flaming combustion 30 to 45 seconds later. By then the sphere is on the ground.
The film below explains the rationale and history of large scale prescribed burning in Australia and how aerial ignition was planned, organized, and executed. Navigation and planning the flight lines was far more complex before GPS became available.