WASHINGTON - Boeing Co on Friday said it will take a $536 million after-tax charge in its second quarter results relating to problems that emerged during testing of the fuel system on the KC-46 aerial refueling tanker aircraft it is developing for the U.S. Air Force. The company said the charge, which amounts to 77 cents per share, reflected higher estimated engineering and manufacturing costs to complete development, certification and initial production of the tanker aircraft, while holding to the program schedule for initial production deliveries in 2017. The company said it was disappointed about the problems, but was determined to keep the program on track for delivering the initial 18 tankers to the U.S. Air Force by August 2017 and building 179 tankers by 2027.