To keep warplanes flying right, Air Force pilots argue that there has to be a "man in the loop" a person in the cockpit. A recently completed investigation into a crash of the Pentagon's most sophisticated unmanned aircraft may reinforce their bias. The Global Hawk, which is under development, is a $45 million drone with a 116-foot wingspan that can fly for more than a day, scouring terrain and relaying video to a ground station 3,000 miles away. Last March a Hawk on a simulated mission surprised its manned F-16 chase plane by rolling onto its back at 400 mph, diving and smashing into the California desert. An investigation found that the plane had even prepared to die: It shut its engine down, erased classified computer data and set its flaps for a death spiral. The investigation also found that at the same time, more than 100 miles away, a second team of Air Force personnel preparing for another Global Hawk test was trying the system's "flight-termination" command. The Hawk, within range of both stations, intercepted the second team's command and dived. It was incapable of distinguishing between the signals. "Things could have been worse," a Pentagon official said. "It could have crashed into the Chinese embassy."