Amazon's private cargo airline increased flight activity 31% in the past year, with much of the expansion recently happening in Europe to support the company's e-commerce business, according to a new report from researchers tracking the retail giant's air logistics operation. The growth in European flight activity took place as Amazon (NASDAQ: AMZN) continued to build out its U.S. air network and position Amazon Air to potentially handle third-party freight beyond its current focus on fast inventory replenishment for warehouses and fulfillment centers.