HOW FAR CAN YOU SEE - PHANTOM - UNAIDED Mark 1 EYEBALL
That depends on a lot of factors but it's generally less than half a mile (1450ft - up to maybe 2200ft if you never look away) if there is good contrast in the background. Let's talk about real world experience, not just theoretical numbers under various conditions. I have 20/20 vision uncorrected so these data points are about as good as it gets for average humans under good conditions. This is for Phantom 4 sized drones ~2ft across, bright white exterior at 100ft AGL with an unobstructed view in direct line of sight with no fog, smog, precipitation or dust and haze. . .
. . . so pretty much OPTIMUM CONDITIONS. Adding a flashing stobe light iStrobe Lightingmproves it a fair bit especially in low light or dark or shadow backdrop. CLICK HERE for more suggestions and videos on that. I have found operating at night, with a STROBON that the Mavic and Phantom4 are still visible at over 6000ft and therefore compliant with new VLOS rules, as of 1 Jun 2019. PART IX 901.11 (1)
Flying here over open water, looking south into bright clear or overcast skies with darker back-lit buildings along the way. You get a clear dark silhouette that you can follow quite easily maybe 2000ft or more if you never look away or get distracted. If you let the drone get down in front of anything but bright sky, it blends in and is lost well before 500ft. There is just not enough contrast to tell it apart from trees towers buildings or terrain..
This was only possible to track it out to 3000ft by finding a clear dark silhouetted object (a smoke stack here) in the far distance and keeping the Phantom (silhouette) just above it. Once it's about 2000ft away you start mixing it up with seagulls or other small faint objects in the sky. If you take your eyes off it or just look away for even a second or two it's GONE and you'll never reacquire it.
Here we are looking BACK at the launch site. Yes you can probably easily see a boat or a plane from 3000ft range, but something the size of a person or a motorcycle is too small to follow let alone a Phantom or Mavic at only 1 ft across.
I placed a small but pretty bright Strobe light on the back of the Phantom and could see it quite well at about 400-450 ft but it was barely distinguishable past that. You can see more about that if you click here.
I'm coming to the realization that NOT allowing BVLOS in ALL cases is really . . in a very practical sense . . has become just a "feel good exercise" for regulators and law makers. In open spaces, there is little Flight Safety value as long as you are watching the UAVs data and camera displays, as long as you can see the airspace around the drone. The Mavic display and data capture is far more accurate and relevant to flight safety than the ability to see a "dot in the sky". A pair of "Mark 1 Eyeballs" have practically NO depth perception beyond a few hundred feet so recognizing a potential course conflict with a larger aircraft in the area, is equally impossible and of little value. The display would tell you far more about a potential mid-air than your eyes. The only option you have is to stay below nearby aircraft in Altitude. In other word you descend if they are anywhere likely to line up in your visual reference field.
I would argue that, operating Beyond Visual Line Of Sight (BVLOS), below 300-400ft, using flight data is safer than eyeballs as long as you are not stretching the telemetry capabilities of the machine you are flying. . .(as long as you can see a normal size aircraft or helicopter in the same airspace ( in VFR conditions) . . . Here a safe margin for range might be "50% of the controller's recommended, tested and demonstrated max telemetry range". For Mavic that's about 10,000ft or 2 miles. That should be fine for all but the pioneer record setters in the tribe. Having a forward observer in the operating area, in communication with the one doing the flying, is a good "Best Practice" non-the-less, to act as an additional safety look-out.
I would recommend that the rules require you to maintain Line of Sight (LOS) whether or not you can actually visually resolve your own UAV/drone. That means not going behind obstacles, buildings or hills etc. . . as long as you don't exceed a safe telemetry limit and you can see larger flight risks like other aircraft in the same airspace that you know you are operating in.
