A cooperative project between the Federal Aviation Administration (FAA) Civil Aeromedical Institute (CAMI), Applied Safety Technologies Corp. (ASTC), and Robert A. Denton, Inc. was conducted to investigate modifications to the standard Hybrid III anthropomorphic test dummy (ATD) lumbar spine and its interface to the pelvis and thorax. The impetus for this project was based on the desires of aviation researchers, manufacturers, and dynamic test laboratories to utilize the Hybrid III ATD in the development and certification of aircraft seats. The goal was to develop a lumbar spine modification for the Hybrid III that would produce similar responses to those measured with a Hybrid II. The primary focus of this project was the compressive force measured at the base of the lumbar column during the vertical test condition required by FAA’s regulations. Analysis of loads imparted to the seat by the Hybrid III, as well as the kinematics of head motion during forward-facing horizontal dynamic impact tests, were also performed as part of this effort.