What does a yellow flag indicate in ground operations?

A yellow flag in ground operations signifies caution. This color is universally recognized in aviation as a warning indicator, advising personnel to proceed with care and be aware of potential hazards in the vicinity. When the yellow flag is displayed, it serves as a reminder to maintain vigilance and to ensure that operations are conducted safely, particularly around moving aircraft or vehicles on the ramp.

The other options do not align with the meaning of the yellow flag. For example, a green flag typically indicates that it is safe to proceed, while a red flag would indicate a stop or hazard that requires immediate attention. A yellow flag does not indicate that maintenance is needed; rather, it emphasizes the necessity for caution during ground operations.