The “development” aspect of the program was particularly true for the legacy FMS, for which IS&S was to replace some—but not all—of the functions. “Delta prohibited IS&S from completely replacing the existing FMS because it contains proprietary algorithms that calculate the optimal vertical flight path to minimize fuel consumption,” says IS&S in the complaint. Delta denies that claim as well as IS&S’s assertion that the airline ultimately canceled the program because it “adopted a new fleet-planning strategy” that calls for replacing the MD-88s and MD-90s. “In short, Delta has changed its mind about the retrofit project and come down with a case of buyer’s remorse,” the complaint argues.