Despite extensive spending since 2001 on intelligence and counterterrorism programs, sophisticated airport scanners and elaborate watch lists, it was something simpler that averted disaster on a Christmas Day flight to Detroit: alert and courageous passengers and crew members. During 19 hours of travel, aboard two flights across three continents, law enforcement officials said, Abdul Farouk Abdulmutallab bided his time. Then, just as Northwest Flight 253 finally began its final approach to Detroit around noon on Friday, he tried to ignite the incendiary powder mixture he had taped to his leg, they said. There were popping sounds, smoke and a commotion...