Abstract: A method of designing an outer air seal for the turbine blades of a gas turbine engine utilizes a knowledge-based product model software program for generating a parametric, three-dimensional, geometric model of the air seal. The product model software program is embodied in a knowledge-based engineering system. The model is created by the program through user selection of various structural feature options available for the air seal. The product model software program uses its internal knowledge base of configuration dependent parameter relationships and rules to design the model. Various types of analyses may then be run to validate the model. The model may be changed, if necessary, as a result of the analyses. The air seal model output from the product model software program is in a file format that defines the topology and dimensions of the geometry of the air seal.