We all remember the tedious work of the manual flight planning required for the Private Pilot certificate, where we spent hours calculating headwind components, ground speeds and, ultimately, the fuel required for the trip. Advanced avionics have made the task of knowing whether you have enough fuel as complicated as entering the fuel remaining and looking at the moving map. A fuel range ring, such as the one on the Garmin G1000, provides a graphical representation of your available range in all directions from your current location.
Provided your avionics has current weather available, the range ring will be anywhere from a perfect circle to an egg shape based on the wind conditions. Naturally, the range line will be farther away from you if you have a tailwind and closer if you have a headwind, creating a semi-oval shape.
Generally, the range ring is the point at which the airplane reaches its fuel reserve (which you can select based on the applicable flight rules or personal preference), so the engine won’t magically quit if your airplane icon touches the dotted line. But regardless, I would personally never allow my destination to cross the line on the screen.
You can adjust the range ring by adding or reducing power and/or leaning the mixture. Obviously your first priority should be keeping the engine happy, but a leaner mixture will extend your range. Some engines allow for lean of peak operations, but this is not territory to enter into without some training because you could damage the cylinders and other components if you use incorrect leaning procedures.
The fuel range ring is a handy tool, but it’s best to err on the side of caution when you enter the fuel remaining. Adding 20 gallons into the system when you actually added 22 gallons to the tanks, for example, provides an added safety margin.