A derrickman was killed when a hoist line failed after the traveling block ran into the rig crown. When the line failed, the traveling block fell, hitting the worker who was in the rod basket (below the rig crown). A flag, attached to the drill line, was being used as a visual aid to stop the hoist when the flag reached the drum. A visual error allowed the block to run into the rig crown. Prevention alert:

• Do not rely on visual references.
• Install an upper travel limit device to guard against line failure.