Section 107.51 of Part 107 sets four numbers for a small drone. Groundspeed is capped at 87 knots, which is 100 mph. Altitude is capped at 400 feet above ground level, with a structure exception. Visibility must be at least 3 statute miles. You must stay 500 feet below clouds and 2,000 feet horizontally from them.
The four limits
| Limit | Value in 107.51 |
|---|---|
| Groundspeed | 87 knots (100 mph) maximum |
| Altitude | 400 feet above ground level maximum, structure exception below |
| Visibility | 3 statute miles minimum from the control station |
| Cloud clearance | 500 feet below, 2,000 feet horizontally |
The 400 foot rule has an exception
The regulation allows flight higher than 400 feet if the aircraft stays within a 400 foot radius of a structure and goes no more than 400 feet above that structure's top. This is the rule that lets inspection crews look at a tall tower or chimney.
Read it carefully. The exception is tied to a structure, and it limits both the horizontal distance and the height above the top. It is not a general permission to climb higher near buildings.
How visibility is measured
Visibility is measured from the control station as the average slant distance at which prominent objects can be seen and identified. By day that means unlit objects. At night it means lit objects. A hazy day can fail the test even when the sky looks clear overhead, so make the check part of your preflight.
Setting these in your flight software
Most flight controllers and ground station apps let you set a geofence and a ceiling. A ceiling in the app is a useful backstop, but it is a convenience and not proof of compliance. The pilot is still responsible for the numbers.
Some practical settings:
- Set the maximum altitude a little below 400 feet so a climb overshoot does not break the limit.
- Check whether your altitude reference is above takeoff or above ground at the site. On sloped ground these differ.
- Use a geofence for jobs near a structure, so the 400 foot radius is enforced by the aircraft.
- Log the real altitude and speed so you can show the flight stayed in bounds.
Waivers
Section 107.51 is on the list of sections a certificate of waiver can authorize deviation from under 107.205. That does not make the limits soft. It means you apply, show an acceptable safety case, and get a certificate before you fly outside them. The waiver topic has its own post in this series.
Quick check
What is the maximum groundspeed under Part 107?
87 knots, which the regulation states is about 100 mph.
Can I fly above 400 feet near a tall structure?
Only within a 400 foot radius of the structure and no more than 400 feet above its top, as 107.51 describes.
Sources
- 14 CFR 107.51, eCFR: operating limitations.
- 14 CFR 107.205, eCFR: list of waivable sections.
Last reviewed: 19 October 2026.
