Site evaluations of air carriers and repair stations conducting inspections and heavy maintenance on PART 121 aging aircraft were conducted during 1989-90 under the FAA's Office of Flight Standards Aging Fleet Evaluation Program. This report presents the findings of the human factors portion of this program in which aspects of the work environment of selected operators were evaluated with respect to illumination levels, noise, temperature/ventilation, work support equipment/workspace adequacy, occupational safety, and extent of worker overtime. Data are reported for 19 site evaluations. While 89 percent of the operators were given global ratings of acceptable or better in the area of human factors, the deficiencies noted were quite consistent across carriers and repair stations. Illumination levels, in particular, were found to be considerably below levels recommended by the Illuminating Engineering Society. There were also deficiencies in work support equipment and in compliance with the operator's stated safety program. Recommendations are given for improvements in each of these areas.