Up near Nova Scotia, I believe. Egyptian airline and I believe it was after 800.
It was Egyptair 990, a Boeing 767-300 heading from Kennedy to Cairo, and it was in the 1997-1997 timeframe.
The NTSB pieced together, from physical wreckage, radar tapes from the New York ARTCC, and the plane's recorders, that the relief pilot (who was a very senior pilot with Egyptair) managed to get himself alone in the cockpit by the ruse of sending the copilot back to give a pen to the captain. (Long international flights have to carry two flightcrews--this guy was supposed to fly the plane over the Atlantic and turn it back over to the designated captain for landing in Cairo.)
When he got alone in the cockpit, he disengaged the autopilot, pulled the throttles back to idle, and pushed the controls forward, quietly chanting something like "I believe in Allah". The captain rushed back to the cockpit, and not knowing what was going on, jumped in the other seat and started pulling the plane up and yelling "pull with me, pull with me." He didn't realize that the suicidal guy was pushing the yoke forward. Then the suicidal one cut the power to the engines, which stopped the flight recorders. Radar info after that showed the plane pulling out of the dive, then diving again into the sea.
The NTSB figured this out because they found indications that one control yoke was being pushed forward and the other pulled backward at the same time. So they ruled that the relief pilot intentionally crashed the plane for reasons unknown.
The Egyptian government angrily denied the NTSB's findings and tried to pin the crash on a design fault--Boeing convincingly shot that down quickly.
}:-)4