2.2.1. Impacts and Challenges. Multicommodity
flow-based fleet assignment models are widely used
by the industry and are credited with achieving
significant cost savings, measuring in the millions
of dollars annually. For example, Rushmeier and
Kontogiorgis (1997) report realized savings of at least
$15 million annually at USAir. Using fleet assignment
models, Wiper et al. (1994) report annual savings
of $100 million at Delta Airlines, and Abara (1989)
reports a 1.4% improvement in operating margins at
American Airlines.
Beyond providing economic benefits, research on
fleet assignment problems has led to advanced techniques
for solving general linear programs. For example,
the node consolidation idea introduced in Hane
et al. (1995), which reduced formulation size by more
than 40% for the problems of one major airline, has
been generalized and incorporated into commercial
solvers, allowing more efficient solution of large-scale
optimization problems.