The B-52 Stratofortress is a legendary aircraft, one of the longest-serving in U.S. military history, even flying missions in Afghanistan and Iraq. But it would not have become the workhorse it is without one disastrous flight 50 years ago next week, when a B-52 on a test run lost its vertical tail fin while on a training flight over the Maine wilderness. The pilot and crew suddenly had seconds to save themselves. The flight, and another six days later in New Mexico, helped to underscore the deadly structural weakness that was later fixed. The Maine flight crashed into a mountainside, killing seven aboard. Two survived. A snowmobile club will hold a remembrance at the Elephant Mountain site on Saturday, in advance of the 50th anniversary Jan. 24.