Unison has provided assistance to a number of airports in developing and revising their airline rates and charges models, and in preparing annual and semi-annual rates and charges calculations. We have performed these services both as part of our on-call responsibilites at many airports, and as stand-alone projects for other clients. Unison has experience in developing airline rates and charges models that reflect an airport's current airline rates and charges methodology. Unison personnel focus on developing a model that is in the format and software most convenient for the client. In either adapting an existing model or developing a new model, Unison ensures that the model is flexible to allow for the creation of "what-if" scenarios to facilitate the evaluation of alternative rates and charges methodologies.