Civil transport aircraft have clearly been demonstrated as a preferred target of terrorist organizations through the years. The threat of the release of a noxious chemical or biological agent into the passenger cabin is real. Protection of occupants is critical for maintaining public confidence in air travel. Therefore, the Federal Aviation Administration (FAA) Civil Aerospace Medical Institute (CAMI) is directing a project for quantitative evaluation of the distribution of contaminants released during mid-flight in commercial airliner passenger cabins. The effort uses the CAMI 747 Aircraft Environmental Research Facility (AERF) to collect airflow data to be used to validate computational fluid dynamics (CFD) algorithms that can predict the potential distribution of a variety of particles in the aircraft. The cabin velocity vector field is measured at a number of points within the cabin using 3-dimensional sonic and conventional hot-wire anemometers. These data serve as a comparison basis to simulation via CFD that predicts the 3-dimensional ventilation flow field. This paper presents the first results of validation of CFD prediction of the cabin flow field in a segment of a 747 AERF. Agreement between the data and the simulation is good, hence represents the first steps towards development of a CFD system to quantitatively study contaminant distribution and assist in testing optimal responses to an attack on various airframes. The release of a chemical weapon has been the focus of work to date, but CFD is ultimately applicable to predicting the distribution of other entities through the aircraft environmental control system (ECS) such as biological, nuclear, or other toxic agents. Concurrently, the approach is applicable to generic cabin air quality issues where an understanding of flow fields is of critical importance in terms of the role that fresh air and.