destination, the city of manaus, nearly four hours to the northwest. air traffic control instructs the "legacy" to fly at 37,000 feet, where it levels off by 3:33 p.m. meanwhile, two minutes later, gol airlines flight 1907 departs manaus for the country's capital of brasilia in the south. within a half hour, the boeing 737 reaches its cruising altitude, 37,000 feet. the 737 is heading southeast. the legacy is heading northwest. the two aircraft should be at different altitudes. instead, they're on a collision course. >> it was a beautiful day, puffy white clouds in the sky, nothing obscuring our view. we took off for what was to be a routine flight. we were flying with very competent pilots in a brand new airplane. what could be bad about that? >> both sets of pilots are in contact with air traffic control, operated by the brazilian air force. but starting at 4:02 p.m., northwest of brasilia, there's a problem. "the legacy's" radar data is no longer being received by air traffic control. >> at some point during the flight, the transponder, which provid