What does a 'hold short' line mean, and how should you respond to ATC instructions to hold short?

• A. Do not cross the line until cleared; acknowledge and stop before the line.
• B. You may cross the line when you see an aircraft approaching.
• C. Stop immediately after crossing the line, even if not cleared.
• D. Hold short lines are advisory; proceed when ready.

Answer: (A)

A hold short line marks a boundary you must not cross without explicit clearance. When ATC says to hold short, you should stop before that line, acknowledge the instruction, and be ready to taxi again only after you’ve received further clearance. In practice, you’d typically respond with a read-back like “Holding short of Runway X” and wait for the next instruction. You do not cross the line just because you see traffic or feel ready.

This is why the other ideas don’t fit: crossing without clearance is not permitted, stopping after you’ve already crossed is not allowed, and hold short lines are mandatory, not merely advisory.