Several fire retardants in current use were dropped from the Canadair CL-215 to determine drop height effects and for evaluation of the tank and gating system. This was accomplished through the quantification and analysis of the characteristics of the ground distribution patterns-such as retardant recovery and pattern contour lengths. The effects of retardant type, load size, drop height and speed, aircraft attitude, and drop conditions on the ground distribution patterns were also determined. Drop height and load size were found to be the most significant variables, affecting almost all measured parameters for the retardants dropped. Covariance analysis of linear drop height models for total recovery indicated the greatest difference existed between the gum-thickened retardants (Phos-Chek XA and Gelgard) and the unthickened or clay-thickened retardants (Fire-Trol 100 and water). The Phos-Chek XA had the greatest recovery, followed by Gelgard, and then Fire-Trol 100 and water. Similar results for contour areas and line lengths occurred in the nonlinear models developed for predicting effects of drop height. The data analysis indicated the optimum drop height for the gum-thickened Phos-Chek XA and Gelgard to be as much as two to five times higher than that for Fire-Trol 100 and water. Thus, effective drop heights and safety may be greatly increased by the use of gum-thickened retardant. The conclusions made were supported by an analysis of drop times and evaporation losses which indicated that the gum-thickened retardants had smaller drop times, greater cohesion, longer stripping times, and a larger mean droplet size after erosion. Evaluation of the tank and gating system of the CL-215 and comparison of its performance with that of other presently used aircraft indicate its line-building efficiency to be equally effective. The performance and flexibility of the CL-215 tank and gating system could be improved, however, if a four-tank or gate system incorporating an intervalometer were adopted rather than the manually sequenced two-gate system.