What might indicate that a tower crane is about to tip over?

Excessive swaying or unusual noises are clear indicators of potential instability in a tower crane. When a crane begins to sway more than usual, it suggests that the mast is experiencing lateral forces that could compromise its balance. This can happen due to sudden changes in wind conditions, abrupt movements while lifting, or excessive loads being placed on the crane. Unusual noises may also signify mechanical issues, such as wear or strain on critical components, which could lead to failure. Observing these signs is crucial, as they provide operators with vital information to assess the crane's condition and take necessary precautionary measures before an accident occurs.

The other options do not indicate impending danger. Calm wind conditions typically suggest stability and safety for crane operations. Consistent lifting of materials is normal operational behavior, indicating that the crane is functioning as intended. Additionally, clear visibility of the load ensures effective communication and monitoring but does not inherently relate to the stability of the crane itself.