The FAA's $40 billion NextGen reforms were meant to update an air traffic control system that had become frustratingly outdated, with pieces that hadn't been changed since the 1960s. NextGen's changes to GPS and landing systems would save fuel, cut miles off airplane flight paths, and prevent airport gridlock. As it rolled out, though, a program that was supposed to simplify how planes navigated the runway and crossed paths in the air became mired in its own set of complicated procedures and red tape. The Wall Street Journal follows NextGen from its inauspicious beginnings to its recent successes, as pilots and passengers are starting to reap the benefits of long-delayed alterations.