Regulations
The 400-Foot Rule: Part 107 Altitude Limits Explained
✓ Reviewed against current FAA sources on October 22, 2026
In this guide
In short
Section 107.51 (opens in a new tab) limits a small unmanned aircraft to 400 feet above ground level, unless it stays within a 400-foot radius of a structure, in which case it may fly up to 400 feet above that structure's uppermost limit. The same section caps groundspeed at 87 knots, requires 3 statute miles visibility from the control station, and requires staying 500 feet below and 2,000 feet horizontally from clouds.
The 400-foot rule is the most quoted number in drone flying and one of the most frequently misquoted. The rule has an exception built into it, and the exception is what the test asks about.
What Section 107.51 (opens in a new tab) actually limits
The section is titled "Operating limitations for small unmanned aircraft," and it sets four things:
- Groundspeed may not exceed 87 knots, which is 100 miles per hour.
- Altitude may not exceed 400 feet above ground level, subject to the structure exception below.
- Minimum flight visibility, observed from the control station, is 3 statute miles.
- Cloud clearance is at least 500 feet below a cloud and at least 2,000 feet horizontally from a cloud.
The structure exception
An aircraft may exceed 400 feet AGL if it remains within a 400-foot radius of a structure and does not fly higher than 400 feet above that structure's uppermost limit.
Both conditions apply together. A 1,000-foot tower does not authorize a 1,400-foot flight across the valley. It authorizes up to 1,400 feet while you stay within 400 feet laterally of the tower. Step outside that radius and the ordinary 400-foot AGL ceiling returns immediately.
Above ground level, not above sea level
The limit is measured from the ground beneath the aircraft, not from the launch point and not from sea level. Flying from a ridge out over a valley, the aircraft can be at a legal height above your position and far above 400 feet AGL over the terrain below it. That is a violation, and it is the scenario examiners like.
Note what the cloud numbers are not
Five hundred feet below and 2,000 feet horizontal are Part 107 figures for unmanned aircraft. They resemble, but are not identical to, the manned aircraft VFR minimums in 14 CFR 91.155 (opens in a new tab), where the pattern is 500 below, 1,000 above and 2,000 horizontal. Part 107 has no "above" figure, because you are not permitted above the cloud in the first place while maintaining visual line of sight.
The visibility figure is measured from the control station
Three statute miles of flight visibility is assessed from where the remote pilot stands, not from the aircraft. The rule defines it as the average slant distance at which prominent unlighted objects can be seen and identified by day, and prominent lighted objects by night.
What a waiver can change
Section 107.205 (opens in a new tab) lists the sections that may be waived, and Section 107.51 (opens in a new tab) is among them. Altitude, speed and visibility limits can all be waived with an approved certificate of waiver, but the waiver must be in hand before the flight, not sought afterward.
Sources: 14 CFR 107.51 (opens in a new tab), 107.205 (opens in a new tab); 14 CFR 91.155 (opens in a new tab).