This research addresses the problem of work assignment to operators in paced manual aircraft assembly lines. In such assembly lines, in contrast to the intensively studied automotive assembly lines, a relatively high number of operators can be assigned to the same workstation. Therefore, a Resource Constrained Project Scheduling Problem (RCPSP) should be solved for each workstation in order to schedule the assembly tasks under the takt time constraint. In addition to precedence, resource and skill constraints, which are common for the RCPSP formulations, this study considers ergonomic constraints. We develop new mathematical models for physical and cognitive ergonomic constraints for operators and show first results for several industrial applications.