Early aviation hydraulic systems were used to apply brake pressure. These systems used a vegetable oil-based hydraulic fluid. As aircraft design produced larger and faster aircraft, greater use of hydraulics was necessary.
These advances led to development of petroleum-based hydraulic fluids such as Mil-O-3580 and, later, Mil-H-5606. Shortly after World War II, the growing number of aircraft hydraulic fluid fires drew the collective concern of the commercial aviation industry and the public....More