Vision and Its Role in Maintaining VLOS
Visual line of sight isn't just a rule about staying within a certain distance of the aircraft — it's fundamentally a rule about human vision, and human vision has real physiological limits and failure modes a remote pilot needs to understand. This lesson explains 14 CFR 107.31's unaided-vision requirement in full, what "unaided" does and doesn't allow, correct visual scanning technique, and a specific visual phenomenon — empty-field myopia — that can quietly undermine VLOS even when a pilot believes they're scanning effectively.
What 14 CFR 107.31 actually requires
14 CFR 107.31 requires that, throughout the entire flight, the remote pilot in command, the visual observer (if one is used), and the person manipulating the flight controls be able to see the unmanned aircraft using human vision unaided by any device other than corrective lenses. That visual capability must be sufficient to know the unmanned aircraft's location, determine its attitude, altitude, and direction of flight, observe the airspace for other air traffic or hazards, and determine that the unmanned aircraft does not endanger the life or property of another. This is a functional requirement, not just a distance rule — you need to actually be able to do all four of those things by looking at the aircraft, not merely be physically close enough that you theoretically could.
What "unaided" does and doesn't allow
"Unaided by any device other than corrective lenses" has a specific, narrow meaning. Corrective lenses — prescription glasses or contact lenses that correct a pilot's vision to normal — are explicitly permitted, because they restore rather than enhance vision beyond what an unimpaired person would have. What is not permitted as a means of satisfying the VLOS requirement is any device that extends vision beyond normal unaided capability: binoculars, telescopic sights, and critically, a first-person-view (FPV) camera feed or any other video display. A pilot watching only a live camera feed, however clear, is not maintaining visual line of sight under 107.31, because the regulation requires the person's own natural vision to be doing the work, not a camera's.
Where binoculars and camera feeds still fit in, legally
This doesn't mean binoculars or camera feeds are banned outright from a Part 107 operation — they simply can't be the thing satisfying the VLOS requirement itself. A pilot can briefly use binoculars to help identify a distant hazard, or reference a live camera feed for photography purposes, as long as the underlying VLOS requirement is still being separately satisfied by someone's unaided vision at all times — either the remote PIC's own eyes when not using the binoculars, or a visual observer's unaided vision covering the aircraft continuously while the PIC's attention is briefly elsewhere.
The visual observer's role in satisfying VLOS
14 CFR 107.33 allows a visual observer to help satisfy the VLOS requirement by maintaining effective communication with the remote PIC at all times, being used to scan the airspace for other air traffic or hazards, and being positioned so they can see the aircraft well enough to perform those functions with their own unaided vision (again, corrective lenses permitted). A visual observer does not replace the remote PIC's own responsibility, but does allow VLOS to be maintained as a team effort — useful, for instance, when the aircraft momentarily passes behind an obstruction from the PIC's position but remains visible from the VO's.
A systematic block scanning pattern sweeps the sky in overlapping sectors with brief pauses, rather than a continuous, unfocused sweep.
View LargerWhy a continuous, unfocused sweep doesn't work
An untrained instinct is to scan the sky with a smooth, continuous sweeping motion of the eyes. The human eye actually detects movement and small distant objects far more effectively when it briefly stops and focuses on a specific area rather than sweeping continuously — a continuously moving eye doesn't have enough time on any one area to detect a small, distant, and potentially fast-moving object like another aircraft. This is the same underlying visual limitation manned aviation pilots are trained around when scanning for other traffic.
The block scanning technique
Effective visual scanning uses a technique often called block scanning: dividing the sky into a series of separate, overlapping sectors (roughly 10 degrees wide each is a commonly taught reference), and briefly stopping to focus on each sector for a second or two before moving to the next, working systematically across the relevant field of view rather than randomly or continuously. This gives the eye enough dwell time on each sector to actually detect a small or distant object, at the cost of taking slightly longer to cover the full field of view than a continuous sweep would — a worthwhile tradeoff given how much more effective it is at actually detecting hazards.
Empty-field myopia: the eye's tendency to lose focus in a featureless sky
Empty-field myopia is a documented visual phenomenon where, in the absence of any object to focus on — such as staring at a clear, featureless sky — the eye's focus naturally relaxes to a near resting distance, often cited as roughly 1 to 2 meters, rather than remaining focused at infinity. In this myopic state, the eye is effectively out of focus for anything actually at a distance, which means a genuinely present but small or distant object (another aircraft, for instance) can be present in the field of view and still go undetected, because the eye isn't optically focused far enough away to resolve it clearly.
Worked scenario: scanning a clear, featureless sky
You're flying an inspection mission under a completely clear, cloudless sky with no visual reference points overhead. After several minutes of scanning without seeing anything unusual, empty-field myopia becomes a real risk — your eyes may be relaxing toward their near resting focus distance precisely because there's nothing distant to lock onto. The correct countermeasure is deliberately shifting focus to a genuine distant reference point periodically — a distant tree line, a cloud edge if any exists, or even your own aircraft itself — to force the eyes back to a distant focal point, rather than assuming an empty-looking sky means nothing is actually approaching.
Without a distant reference point, the eye's focus relaxes toward a near resting distance, blurring genuinely distant objects like another aircraft.
View Larger| Item | Permitted under 107.31? | Why |
|---|---|---|
| Prescription glasses or contact lenses | Yes | Corrective lenses restore normal vision rather than extending it beyond normal capability |
| Binoculars as the sole means of maintaining VLOS | No | Extends vision beyond unaided human capability; not "unaided" vision as the rule requires |
| FPV or live camera feed as the sole means of maintaining VLOS | No | The regulation requires the person's own natural vision to be doing the work, not a camera |
| A visual observer's unaided vision supplementing the PIC's | Yes | 14 CFR 107.33 allows VLOS to be maintained as a team effort using each person's own unaided vision |
Scanning the Sky Effectively During a Mission
Apply this technique continuously throughout the flight, not just at launch and landing.
Divide your field of view into sectors
Mentally break the relevant sky into a series of roughly 10-degree overlapping sectors covering the area you need to monitor.
Pause briefly on each sector
Stop your eye movement on each sector for a second or two before moving to the next, giving your eye enough dwell time to actually detect small or distant objects.
Deliberately refocus on a distant object periodically
In a clear or featureless sky, periodically shift focus to a genuine distant reference point to counter empty-field myopia's tendency to relax focus toward a near distance.
Keep camera and controller glances brief
If checking a live video feed or controller display, keep the glance brief and return to unaided scanning of the actual aircraft immediately afterward.
Coordinate with a visual observer if one is present
Confirm the VO is actively scanning and communicating, not simply standing nearby, so VLOS is genuinely being maintained as a team effort per 14 CFR 107.33.
| Mistake | Why it happens | Correct understanding | Regulation / source |
|---|---|---|---|
| Believing a clear FPV or camera feed satisfies the VLOS requirement | The feed shows the surrounding area clearly, which feels equivalent to seeing it directly | 107.31 requires unaided human vision; a camera feed is explicitly not "unaided" vision. | 14 CFR 107.31 |
| Scanning the sky with a continuous, smooth sweep | A continuous sweep feels like it covers more area, more thoroughly | The eye detects small or distant objects far better with brief pauses on each sector than with continuous movement. | FAA Risk Management Handbook |
| Assuming a clear, empty-looking sky means no traffic is present | A featureless sky appears to have nothing to see | Empty-field myopia can cause the eye's focus to relax to a near distance, blurring a genuinely present distant aircraft. | FAA Risk Management Handbook |
Can I wear sunglasses while maintaining VLOS?
14 CFR 107.31(b) permits corrective lenses; ordinary non-prescription sunglasses are not explicitly addressed the same way, but they don't extend vision beyond normal capability the way binoculars or a video feed would, and are commonly used in practice for glare reduction while maintaining unaided vision of the aircraft.
If my visual observer loses sight of the aircraft briefly, is that automatically a violation?
The requirement is that VLOS be maintained by the remote PIC, VO, or person manipulating the controls throughout the flight collectively — a brief individual lapse by one person is a concern to address immediately (regaining sight or having someone else confirm coverage), but the regulation is about the operation maintaining VLOS overall, not a single instant of one person's view.
Is empty-field myopia something that only affects inexperienced pilots?
No. It's a physiological property of how the human eye focuses in the absence of a visual reference, and it affects any pilot regardless of experience — the countermeasure (deliberately refocusing on a distant reference point) is a learned habit, not something experience alone eliminates.
Test Your Knowledge
Answer the questions below to check your understanding. Every answer can be found in the lesson above.