The F-35 joint program office will kick off its Block 4 modernization program six to 12 months late because the program's requirements are not validated, according to an official. Air Force Lt. Gen. Christopher Bogdan, F-35 program executive officer, told reporters Feb. 10 that the requirements for Block 4 will go before the Air Force Requirements Oversight Council and the Joint Requirements Oversight Council this spring. Block 4 is a follow-on effort for the Joint Strike Fighter. It includes additional...