LOS – Line off Sight.
VLOS – Visual Line of Sight.
means unaided (corrective lenses and/or sunglasses exempted) visual contact with the aircraft sufficient to be able to maintain operational control of the aircraft, know its location, and be able to scan the airspace in which it is operating to decisively see and avoid other air traffic or objects.
Vision enhancing devices such as binoculars, night visual goggles, powered vision magnifying devices and goggles designed to provide a first person view are not considered “unaided visual contact”. In determining the range that will ensure the UAV can be seen, consideration must be given to the pilot or visual observer capabilities, the meteorological conditions, the size and conspicuity of the UAV and any other relevant factors.