Air Transport Services Group, Inc. (NASDAQ:ATSG), a global leader in medium widebody freighter aircraft leasing, air transport operations, and support services, Monday announced the expiration of the 35-day “go-shop” period under the terms of the previously announced definitive merger agreement, pursuant to which Stonepeak, a leading alternative investment firm specializing in infrastructure and real assets, will acquire ATSG for $22.50 per share in cash.