“It is immensely difficult to find ways to add another digit to this field, and it’s really only a problem for three airlines in the world.”
American, Delta and United want to number more than 9,999 flights on systems that date to the 1960s. American runs a model to conserve flight numbers and reuses them on out-and-back trips. Its network planner says adding a fifth digit would be too great a technology investment. CEO Robert Isom says American has “aspirations to be a lot bigger.” The four-digit field disagrees.