When people ask what the rules are for flying a drone commercially in the United States, the answer has a precise legal home: 14 CFR Part 107, the Federal Aviation Administration's regulation for small unmanned aircraft systems. Part 107 applies to drones weighing less than 55 pounds and covers the routine, non-recreational operations most commercial pilots run. The rule is not a checklist of tips. It is codified federal law, and its operating limits are written as hard numbers a remote pilot in command must meet.

The single section that defines the flight envelope is 14 CFR 107.51, "Operating limitations for small unmanned aircraft." It states that groundspeed "may not exceed 87 knots (100 miles per hour)," that altitude "cannot be higher than 400 feet above ground level" unless the aircraft is within a 400-foot radius of a structure and stays no higher than 400 feet above that structure's uppermost limit, and that minimum flight visibility from the control station must be "no less than 3 statute miles." The section also fixes cloud clearance at 500 feet below and 2,000 feet horizontally. Each limit is a number in the regulation, not a recommendation.

The altitude of the small unmanned aircraft cannot be higher than 400 feet above ground level, unless the small unmanned aircraft: (1) Is flown within a 400-foot radius of a structure; and (2) Does not fly higher than 400 feet above the structure's immediate uppermost limit.— 14 CFR 107.51, source

What "visual line of sight" actually requires

The limit that does the most to bound where a Part 107 drone can go is not in the speed-and-altitude section. It is 14 CFR 107.31, "Visual line of sight aircraft operation." The rule requires that, "with vision that is unaided by any device other than corrective lenses," the remote pilot in command, the person manipulating the controls, and any visual observer must be able to see the unmanned aircraft throughout the entire flight. The regulation then states the four things that visibility is for: to know the aircraft's location; to determine its attitude, altitude, and direction of flight; to observe the airspace for other air traffic or hazards; and to determine that the aircraft does not endanger the life or property of another.

That "unaided by any device" language is the load-bearing phrase. It means the pilot's own eyes, with glasses or contacts permitted, must maintain the watch — a first-person-view camera feed does not satisfy 107.31. This is the regulatory wall that separates ordinary Part 107 flight from beyond-visual-line-of-sight (BVLOS) operations, which require a separate waiver or authorization. The rule does allow the watch to be kept by a visual observer in lieu of the pilot under 107.31(b), but the requirement to keep the aircraft visible never lapses during the flight.

Where the boundary of the rule sits

Read together, 107.31 and 107.51 define a deliberately conservative box: low, slow, in clear air, and always in sight. The altitude ceiling of 400 feet keeps small drones below most crewed-aircraft traffic; the 3-statute-mile visibility minimum and cloud-clearance distances keep the operation in conditions where the see-and-avoid duty of 107.31 can plausibly be met; and the 100-mph speed cap bounds the kinetic energy of any aircraft operating under the rule. The structure-radius exception in 107.51(b) is the one place the 400-foot ceiling flexes — it lets an inspection drone climb alongside a tall tower or building, provided it stays within 400 feet of that structure and no more than 400 feet above its top.

None of these limits is absolute in the sense of being unwaivable. Part 107 contains its own waiver mechanism, and a separate FAA regulation, 14 CFR Part 89, layers a remote-identification broadcast requirement on top of Part 107 flight. But the baseline a commercial small-drone pilot operates under, absent any waiver, is exactly what these two sections say: keep it under 400 feet, under 100 miles per hour, in at least 3 miles of visibility, and within unaided visual line of sight from takeoff to landing. The text of the regulation is the authority, and it is public and verifiable in the eCFR.

The visibility section carries its own internal definition that matters when conditions are marginal. Section 107.51(c) specifies that "flight visibility means the average slant distance from the control station at which prominent unlighted objects may be seen and identified by day and prominent lighted objects may be seen and identified by night." The measure is therefore taken from the control station, not from the aircraft, and it is a slant distance rather than a horizontal one — a detail that ties the visibility minimum directly to the see-and-avoid duty the pilot owes from the ground.

The cloud-clearance numbers in 107.51(d) work the same way. The rule fixes the minimum distance from clouds at no less than "500 feet below the cloud" and "2,000 feet horizontally from the cloud," two separate measurements that both have to be satisfied. Read alongside the 3-statute-mile visibility floor, these distances keep a small drone in air clear enough that an operator can plausibly spot and avoid other traffic, which is the safety purpose 107.31 assigns to the watch.

Who has to hold the watch

Section 107.31 is explicit that the visual line-of-sight duty is shared and never optional during flight. Paragraph (a) names three roles who must be able to see the aircraft "throughout the entire flight" — the remote pilot in command, the visual observer if one is used, and the person manipulating the flight controls. Paragraph (b) then states that the ability described in paragraph (a) "must be exercised by either" the remote pilot in command together with the person manipulating the controls, or a visual observer. The rule allows the watch to shift to a visual observer, but it does not allow it to lapse, and it does not let any one of those parties rely on a device other than corrective lenses to keep the aircraft in sight.

For operators, the practical consequence is that compliance is a matter of reading the numbers and the verbs. The regulation uses "may not," "cannot," and "must" — mandatory language. A flight that exceeds 400 feet without qualifying for the structure exception, or that relies on a camera feed rather than eyes for the see-and-avoid duty, is outside Part 107 unless a waiver authorizes the deviation. The rule's precision is what makes it citable: every limit traces to a section number in Title 14 of the Code of Federal Regulations.