The first officer saw a bright object ahead of the plane -- the planet Venus -- and mistook it for the approaching C-17. The captain corrected him and said the C-17 was straight ahead and 1,000 feet below.
At that point, the captain of the Air Canada jet and the C-17 pilots flashed their planes' landing lights at each other to acknowledge their position.
But the first officer, still believing that the object in the sky above him was the cargo plane, initiated a dive to avoid the perceived imminent collision -- sending the jetliner toward the Air Force plane.
The captain saw what was happening and immediately pulled back on the control column in a frantic attempt to increase altitude. As quickly as that, the C-17 passed underneath the Air Canada jumbo jet with 103 people on board.