However, the advent of premium air carriers such as Federal Express and United Parcel Air introduced scheduled global airfreight service. While such premium service was originally targeted at high-priority documents, it has expanded to include package freight. For example, premium carriers have integrated their service to include overnight parts delivery from centralized distribution centers located near their air hubs. Overnight air delivery from a centralized warehouse is attractive to firms with a large number of high-value products and time-sensitive service requirements