W5PROTOOLS / FAA TOWER

14 CFR 77.9 · 47 CFR 97.15(a) · Part 17

Tower height & FAA notice check

Planning a tower or mast? Amateur antenna structures taller than 200 ft, or close enough to a public-use airport or heliport to stick through its imaginary slope surface, need an FAA notice (Form 7460-1) before you build. This tool runs the same height and slope tests. It's a screening aid only. The FAA's own Notice Criteria Tool gives the official answer.

Site & structure

Top of the highest antenna or mast, measured from the ground at the base. On a building, include the building.

Before you build

  • Confirm with the FAA's Notice Criteria Tool (OE/AAA). It's the authoritative screen. It also checks things this tool doesn't, such as frequencies near FAA facilities.
  • If notice is required, file FAA Form 7460-1 through OE/AAA. 14 CFR 77.7(b) says to file at least 45 days before construction starts.
  • A structure that needs FAA notice must also be registered with the FCC (Antenna Structure Registration, 47 CFR 17.4) unless an exception applies. The FCC's TOWAIR tool runs the same 17.7 screen.
  • Not evaluated here: the shielding exception of 77.9(e)(1), which can apply when an existing structure or terrain of equal or greater height shields the object in a congested area. You can't claim it on your own judgement, so file and let the FAA decide. Also not evaluated: construction on airport property (77.9(d)), private-use airports and heliports that have an instrument approach (77.9(d)(4)), and FAA requests under 77.9 or 17.7(c).

How it works

Height rule. 14 CFR 77.9(a): notice is required for anything more than 200 ft (60.96 m) above ground at its site. 47 CFR 97.15(a) applies this to amateur antenna structures through Part 17 of the FCC rules.

Slope rule. 77.9(b): notice is required if the structure's top would stick through an imaginary surface that rises from the nearest point of the nearest runway:

  • 100:1 out to 20,000 ft, for airports whose longest runway is more than 3,200 ft;
  • 50:1 out to 10,000 ft, for airports whose longest runway is 3,200 ft or less;
  • 25:1 out to 5,000 ft from the nearest landing and takeoff area of a heliport.

The comparison is made above sea level: (ground elevation + structure height) against (airport elevation + distance ÷ slope). For example, 10,000 ft from a 5,000-ft runway the surface is 100 ft above the airport's elevation. Exception: under 77.9(e)(4) an antenna structure of 20 ft or less needs no notice, unless it raises the height of another antenna structure.

Airport data is the FCC's own list of the facilities that the Part 17 slope test is measured from (“Airport Facilities — 47 CFR Part 17”: Airport.txt and Runway.txt, file date 3 Sep 2026, downloaded 1 Oct 2026; 5,447 facilities). Distances are to the nearest point of each runway centreline or helipad, from coordinates published to the nearest arc-second (about 30 m). About 600 facilities have no runway coordinates in the file. For those, the distance is measured from the airport reference point, minus half the longest runway, and is marked “≈”. The surface starts at the published airport elevation, which is the highest point of the usable runways. The FAA's own tool may use the elevation at the nearest runway end, which can be lower.

Ground elevation comes from the USGS Elevation Point Query Service (3DEP, US only) when you press USGS. A surveyed or GPS value works just as well.

Location precision matters. A 6-character grid square is about 9 km × 4.6 km, which is about as wide as the whole 100:1 zone. Use coordinates (or an 8- or 10-character locator) for a real answer.

  • 14 CFR 77.9, “Construction or alteration requiring notice” (eCFR, current as of 29 Sep 2026).
  • 47 CFR 17.7, “Antenna structures requiring notification to the FAA”, and 17.4 (registration) (eCFR, 29 Sep 2026).
  • 47 CFR 97.15(a), “Station antenna structures” (eCFR, 29 Sep 2026).
  • FCC, “Airport Facilities — 47 CFR Part 17” files, fcc.gov/uls/transactions/daily-weekly.
  • USGS 3DEP Elevation Point Query Service, epqs.nationalmap.gov.