Online retail titan Amazon is starting up its own air cargo service, laying down a challenge to companies like Fedex and UPS, which currently deliver much of its goods. Aircraft leasing firm Air Transport Services Group (ATSG) said Amazon's Fulfillment Services unit will lease 20 Boeing 767 freighters, to be operated by ATSG, to serve Amazon customers in the United States."A dedicated, fully customized air cargo network can be a strong supplement to existing transportation and distribution resources," read a statement from ATSG chief executive Joe Hete. "We are excited to serve Amazon customers by providing additional air cargo capacity and logistics support to ensure great shipping speeds for customers."Dave Clark, Amazon senior vice president of worldwide operations and customer service, said the move was to "ensure air cargo capacity to support one and-two-day delivery for customers."It could boost Amazon's standing with customers, especially during the heavy shopping of the end-of-the-year Christmas period. Over the past two years both UPS and Fedex have struggled to meet delivery commitments given the high volume of goods ordered online.