2006 Annual Report 4d.Progress report. This report serves to document research conducted under a Specific Cooperative Agreement between ARS and Houma Avionics, Inc. Additional details of research can be found in the report for the inhouse project 6402-22000-038-00D, Development of Pesticide Application Technologies for Spray-Drift Management and Targeted Spraying. A variable-rate aerial application system that included the AutoCal II flow controller and SATLOC M3 guidance system was evaluated in the field. Data from the AutoCal automatic flow controller and an improved flow meter circuit were used to assess flow controller error and variable rate system error. Data were collected while making applications to a series of four management zones (each zone required approximately 1.2 s) with application rates of 28, 47, 56, and 37 L/ha. Areas under time plots of required and actual flowrates were compared, indicating flow controller error ranging from -1.0 to 2.1 percent, with an average of 0.77 percent. Variable rate system error due to rate change timing was evaluated by comparing required rates from the system to required rates from the prescription. Area under time plots of these variables showed that average rate timing error for six application passes ranged from -9.1 to 1.4 percent with an average of – 3.04 percent. The significance of working directly with a manufacturer of state-of-the-art equipment is that improvements are immediately available to the aerial applicators who are the primary customers of this work.