An important aspect of the program and an area that has been the subject of some controvery is that of cost and affordability. Typically cost modelling for aircraft systems has encompassed two major classes of tools. The first charaterizes the relationship between aircraft cumulative quantity and unit cost and is popularly known as the learning curve and referred to more generally as the cost progress function. A common thread between the two classes of tools is the use of historical data and statistical analysis to define the functional relationships.
Building models derived from historical data has advantages and disadvantages.
The greatest advantage is that the models are based on a proven level of cost perfromance evident in the historical data. In this sense, they are totally objective and not dependent on anyone's claim of costs that can be accomplished. In the past this has not proven to be a large problem for estimating the costs of aircraft structure, as the functional relationships defining both cost progress functions and CERs have been stable over several decades. However, it is the position of the aircraft manufacturers, backed up by some anecdotal evidence, that the revolution in digital design and manufacturing has begun to exert downward pressure on costs, at least at the level of the factory floor. Although it is the nature of the cost models to be dependent on historical data, the models may be specified in such a way as to better capture the effects of changes in technology and environment.