Section 107.31 says, “(a) With vision that is unaided by any device other than corrective lenses, the remote pilot in command, the visual observer (if one is used), and the person manipulating the flight control of the small unmanned aircraft system must be able to see the unmanned aircraft throughout the entire flight in order to:
(1) Know the unmanned aircraft’s location;
(2) Determine the unmanned aircraft’s attitude, altitude, and direction of flight;
(3) Observe the airspace for other air traffic or hazards; and
(4) Determine that the unmanned aircraft does not endanger the life or property of another.”
Important Note: Using the assumptions below, we can calculate the estimated maximum distance that a person can comply with (1) and (3) but NOT (2) and (4) which are very dependent upon the aircraft design and maybe lighting. In other words, do not just type in some numbers and think you are complying with all of 107.31 by staying within the distance given. You will need to also do an analysis to see if you are complying with (2) & (4).
This is a best case scenario. Please don’t miss this point. It’s the BEST case using the following assumptions.
This assumes optimal conditions:
+Having 20/20 vision. If you don’t, you’ll start losing it earlier.
+Doing on-center viewing using your fovea.
+Operating during daylight hours (not low light),
+ There is no fog, haze, smog, smoke, and
+Have an aircraft which has color contrasting enough from the sky. This is a very important point as many drones are non-contrasting with some white color. You might need to color the aircraft (maybe red plastidip?) to get optimal contrasting.
Step 1. Find the dimensions of your aircraft. You’ll normally end up with two that are the cross section of the aircraft depending on which way you look at it. Think about it. You only really see the sides at a slant angle but rarely look at the drone straight up from the ground. You want to measure the “meat” of the aircraft. Yes, this is open to interpretation but no one is going to see propellers. You’ll see motor to motor for a quadcopter.
Step 2. Put in the smallest cross section dimension of the aircraft in INCHES to be conservative.
Step 3. The result will be the BEST CASE SCENARIO of the distance in FEET you’ll lose sight of the aircraft. Remember this is calculated based upon the smaller dimension so losing visual contact with the aircraft will also be dependent on whether you are viewing the smallest dimension or the largest. For some aircraft which have an aircraft profile of almost a box, you pretty much lose visual contact in whatever orientation the aircraft is.
HOW CAN YOU USE THIS NUMBER?
This number is valuable for determining (1) if you can do a job without relocating on the ground and (2) making sure you NEVER go beyond this number because the FAA, or a clever attorney, would have fun with you if that shows up in your flight logs.
Disclaimer Notice: The final number represents an approximation and should only be used as a guide. No guarantees or warranties are implied. This calculator is “as is” and you should use it at your own risk.