Measurement of a cost function for US airlines: restricted and unrestricted translog models

Abstract

This paper continues and expands several themes from previous studies of commercial airline cost functions. A well specified industrial cost function reveals characteristics about the market players, such as economies of scale and the cost elasticities with respect to operational styles. Using a translog specification, and its restricted first-order form, this paper updates previous parameter estimates, reworks the experimental design, and gives new analysis to describe the spectrum of choices facing airline firms in recent years. The translog model in this paper allows the energy cost share to interact with other variables and illuminate what factors may exacerbate cost sensitivity to energy prices, an advance in this specific area of interpretation. The result shows that fuel cost shares tend to be higher with older equipment, smaller fleet sizes, and to be increasing in aircraft size and seating density. The restricted first-order model indicates that older aircraft designs are more costly to operate, even accounting for operational style. This may imply that airlines with poorer access to capital suffer a cost disadvantage, particularly during a fuel spike - also a new contribution of the paper. Finally, the first-order model does not reject constant returns to scale (CRS) for fleet expansion, or increasing returns to scale (IRS) in aircraft size, which are the expected results.