What does 'running fix' mean?

• A. Fix obtained by advancing line of position
• B. A fix obtained by star sightings
• C. A fix derived from radar range
• D. A fix using GPS

Answer: (A)

A running fix is built by taking a line of position you already have and moving it forward in time along your estimated path, using your speed and the elapsed time. This propagates that line to the present moment so you can determine your current position even between observations. In practice you advance the line of position and then use another observation (like a second line of position or a range measurement) to intersect and pinpoint where you actually are now. This approach specifically describes updating a prior LOP by advancing it, which is what a running fix is designed to do.