Five types of aviation hydraulic fluid were examined — mineral, snuffer, phosphate ester, siloxane, and chlorosilicone.

Statistics show that more aircraft accidents are associated with wheel brakes than with any other components. A hot brake test simulating conditions that could develop from a fractured hydraulic pipe during braking revealed little difference in the ignitability of phosphate esters, mineral type and a snuffer fluid D.

Only one fluid, a snuffer fluid C, withstood ignition with brake heat pack temperature of 700C.

Several well known simpler laboratory techniques were used. Of these a combined high pressure spray/manifold test not only gave a reasonable degree of correlation with the hot brake test results, but also differentiated between the degree of flame propagation evidenced by these fluids.

The shape of the nozzle in the spray tests influenced results whilst fluid temperature and pressure were found to have generally little significant effect.