Which signal indicates entering the lock?

• A. Flashing Red
• B. Flashing Amber
• C. Flashing Green
• D. Flashing Amber and Green

Answer: (C)

In lock operations, signals tell you when it’s safe to move into the lock chamber. A flashing green signal directly communicates clearance to enter—the lock is ready, gates are aligned, and it’s safe to proceed into the chamber.

Red is a stop signal, so you would hold and wait. Amber signals caution or that you should slow down or prepare for the next step, not enter. A flashing amber and green isn’t the standard entry clearance, so it wouldn’t be the signal to enter. When you see flashing green, you enter the lock in a controlled, orderly manner, following the lock operator’s instructions.