In order to be operating within visual line of sight (VLOS), either the operator or a visual observer (VO) must be able to see the UA (with vision unaided by any device other than corrective lenses) throughout the entire flight to ensure it does not present a collision hazard to other manned aircraft or persons or property on the ground.
Source: Page 7, 2.2.3.1, faa.gov/documentLibrary/media/Advisory_Circular/AC_91-57C_FAA_Revised.pdf
Question: The wording says you must "be able to see the UA" and it doesn't say you must continuously see the UA. Is this ambiguous? Being "able to see" means you could look away for periods of time, such as looking at your RC, so long as you could look up and see the UA if you wanted to. Am I understanding this correctly? Or must you continuously have eyes directly on the drone without looking away, in which case, how could you ever look at your RC?
If you can look away, is there guidance on for how long you can look away? For how much of your flight could you be looking at your RC and not the drone, so long as you are still "able to see" the drone if you wanted to? Could you fly the whole flight looking at your RC, so long as you are "able to see" the drone if you want to?