Por UAV Meteo Editorial Team · 9 min de lectura

Part 107 Weather Minimums: Visibility, Cloud Clearance and Altitude Explained

If you fly under the FAA's Part 107 rule in the United States, the weather minimums you're legally required to observe aren't a vague "use good judgment" standard — they're four specific, numeric limits written into 14 CFR § 107.51. This guide walks through each one, in the regulation's own language, and maps it to what UAV Meteo can and can't tell you about it.

Jurisdiction note: 14 CFR Part 107 is a United States Federal Aviation Administration (FAA) rule and applies to operations conducted under US airspace jurisdiction. If you fly elsewhere, your civil aviation authority (EASA in the EU, UK CAA, Transport Canada, CASA in Australia, and others) sets its own — often different — numeric limits. Everything below is specific to Part 107; treat it as a US reference, not a universal standard.

The four limits in 14 CFR § 107.51

Section 107.51 is short enough to quote directly. As of this writing, it requires that "a remote pilot in command and the person manipulating the flight controls of the small unmanned aircraft system must comply with all of the following operating limitations when operating a small unmanned aircraft system":

(a) Groundspeed: 87 knots (100 mph)

The small unmanned aircraft's groundspeed may not exceed 87 knots (100 mph). This is a hard ceiling on the aircraft's speed over the ground — not airspeed, and not a speed rating for the aircraft in still air. Wind adds to or subtracts from your groundspeed depending on direction: flying with a tailwind pushes your groundspeed up above your aircraft's still-air speed, while a headwind reduces it. For most consumer and prosumer multirotors flown well within their normal operating envelope, 87 knots (about 161 km/h) is rarely the binding constraint — you're far more likely to hit a manufacturer wind-resistance limit first. It becomes genuinely relevant for faster fixed-wing UAS or FPV aircraft with a high top speed, especially with a strong tailwind added on top.

(b) Altitude: 400 feet above ground level

The aircraft's altitude cannot exceed 400 feet above ground level (AGL), unless it's flown within a 400-foot radius of a structure and does not fly higher than 400 feet above that structure's immediate uppermost limit — the "structure exception" that lets you, for example, inspect a 500-foot tower up to 900 feet AGL, as long as you stay within 400 horizontal feet of it throughout the climb.

400 feet AGL is approximately 122 meters. UAV Meteo's Wind by Altitude panel models wind at 10m, 80m, 120m and 180m — so the 120m row sits almost exactly at the Part 107 ceiling, and the 180m row is above it, relevant mainly if you're operating under the structure exception, a waiver, or a different jurisdiction's higher limit.

(c) Minimum flight visibility: 3 statute miles

The minimum flight visibility, observed from the location of the control station, must be no less than 3 statute miles (about 4.8 km). The regulation defines this precisely: "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."

Two words matter enormously here: observed and slant distance. This is not a forecast number — it's what you, standing at your control station, can actually see and identify right now, along the sightline to where your aircraft is operating. See "What UAV Meteo can and can't check for you" below for exactly why that distinction matters.

(d) Minimum distance from clouds: 500 ft vertical, 2,000 ft horizontal

The small unmanned aircraft must stay no less than 500 feet below any cloud, and no less than 2,000 feet horizontally from any cloud. Unlike the visibility requirement, this one is about the aircraft's actual position relative to cloud, not what's visible from the ground — a clear, high-visibility day can still put you inside the 2,000-foot horizontal buffer of a nearby low cloud bank.

What UAV Meteo can and can't check for you

This is the section most drone-weather sites skip, and it's the reason a blanket "not certified for legal flight planning" disclaimer isn't actually useful to you — it tells you not to trust the tool without telling you what specifically to double-check yourself. Here's the specific breakdown, metric by metric:

Wind at altitude (b, partially a). UAV Meteo's Wind by Altitude tool gives you real modeled wind speed and direction at 120m — right at the 400-foot AGL ceiling — which is genuinely useful for pre-flight planning near the altitude limit, and for estimating how much a headwind/tailwind will shift your groundspeed toward or away from the 87-knot limit. What it can't do: confirm your actual altitude in flight (that's your own altimeter/flight controller telemetry) or your instantaneous groundspeed (aircraft speed plus wind vector, which changes throughout a flight).

Visibility (c) — the most important caveat on this page. UAV Meteo's Visibility card is a weather-model forecast of atmospheric visibility for a location, generated before you ever step outside. Section 107.51(c) requires an observed, on-scene, slant-distance visibility check — a fundamentally different measurement, taken by you, at your control station, at the moment of flight. A forecast showing 10km visibility is a reasonable planning signal that conditions are likely to support legal flight visibility later that day; it is not, and cannot be, a substitute for looking at prominent objects on your actual horizon and confirming you can identify them at 3 statute miles before you fly. Use the forecast to decide whether a flight is worth planning at all — never as your sign-off for (c) itself.

Cloud clearance (d) — a genuine gap, stated plainly. UAV Meteo shows cloud cover as a percentage (how much of the sky is obscured), not cloud base height (how far below you the cloud layer actually sits). These are different things: a sky that's 80% covered by a high cloud deck several thousand feet up poses no 500-foot clearance problem at all, while a sky that's only 20% covered by a low, scattered deck can absolutely put you inside the 500-foot/2,000-foot buffer if you're climbing toward it. UAV Meteo's cloud cover trend is a useful early-warning signal — rapidly increasing cover often precedes a lowering ceiling — but it cannot tell you the one number 107.51(d) actually requires. For an actual ceiling height, check a METAR/TAF for the nearest airport (many small-airport METARs are public and free) or use your own visual judgment on the day.

Daylight (related, not part of 107.51 itself). UAV Meteo's Daylight card and Golden Hour Calculator show sunrise, sunset and twilight times for your exact location and date — directly useful groundwork if your operation needs to stay within, or intentionally extend into, a specific daylight/twilight window, though the specific lighting-equipment rules for operating outside full daylight are a separate topic from the weather minimums covered here and are outside this guide's scope.

A worked example

Say UAV Meteo shows, for your planned time and location: Visibility 9 km, Wind (10m) 14 km/h, Wind at 120m 31 km/h, Cloud cover 45%. Here's how that maps to a real pre-flight check against 107.51:

(a) Groundspeed: Neither wind reading is remotely close to pushing a typical multirotor's groundspeed toward 87 knots — not a concern for this flight.
(b) Altitude: If your flight plan tops out at 120m (394 ft), you're just inside the 400 ft AGL ceiling; the 31 km/h reading at that height is the number to check against your aircraft's actual wind rating, not against 107.51 directly.
(c) Visibility: The 9 km forecast is a good sign, but it's not your answer — stand at your control station before launch and confirm you can identify a genuinely distant, prominent landmark. If you can't get a fix on anything past a couple of kilometers despite the forecast, trust what you see, not the number on the screen.
(d) Cloud clearance: 45% cover with no reported ceiling data on hand means you still need to eyeball your actual vertical and horizontal clearance from the nearest cloud bank, or check a nearby METAR if one's available.

FAQ

Does UAV Meteo automatically tell me if I meet Part 107 minimums?

No, and no drone-weather app honestly can — see "What UAV Meteo can and can't check for you" above. UAV Meteo's ratings (Good / Caution / Not Suitable) are its own general flyability methodology for typical consumer/prosumer aircraft, described in full on our How UAV Meteo Works guide; they are not a Part 107 legal-compliance check, and a "Good" rating on UAV Meteo is not equivalent to a confirmed pass against 107.51.

Is 3 statute miles the same as UAV Meteo's visibility reading?

They're measured differently (a forecast model estimate vs. your own on-scene observation), and 3 statute miles converts to roughly 4.8 km if you want a rough planning reference — but the regulation requires the observed figure, not the forecast one. Always confirm visually before flying, especially when the forecast sits close to that threshold.

What if I'm flying under a Part 107 waiver with different limits?

A waiver can specifically authorize operation outside one or more of 107.51's limits (for example, beyond 400 feet AGL for a structure inspection, or below the standard visibility minimum for a specific, mitigated operation). If you hold a waiver, your waiver's own specific conditions govern, not the base rule described here.

I don't fly under Part 107 — does any of this apply to me?

The specific numbers (87 knots, 400 feet, 3 statute miles, 500/2,000 feet) are Part 107-specific and won't match your own country's rule. The underlying categories of limit — a speed cap, an altitude ceiling, a visibility minimum, and a cloud-clearance buffer — are common to most national drone regulations in some form, so the structure of this guide (and the "what your weather app can/can't check" distinction) is worth applying to whatever numeric limits your own aviation authority actually publishes.

This article explains a specific regulation as a reference; it is not legal advice and is not a substitute for reading 14 CFR § 107.51 itself or consulting the FAA/your own aviation authority for your specific operation. Regulations are amended over time — always confirm the current text at ecfr.gov before relying on any specific figure. See our legal & disclaimer page for details.