TOKYO — As smoke filled the cabin of Japan Airlines Flight 516 after its fiery landing in Tokyo on Tuesday, the sound of a child’s voice rose above the din of confusion onboard. “Please, let us off quickly!” the child pleaded, using a polite form of Japanese despite the fear washing over the passengers as flight attendants began shouting instructions. In the minutes that followed, even as the flames that would eventually engulf the JAL plane flickered outside the windows, order held. The attenda