FAA 1A survey and FAA 2C survey: certification letters for Form 7460-1 and as-built towers
An FAA 1A survey is a field survey by a licensed land surveyor that certifies a structure's latitude, longitude, ground elevation and height to within 20 feet horizontally and 3 feet vertically. A 2C letter certifies the same numbers to within 50 feet and 20 feet. Tower owners, carriers, developers and crane contractors order one to support an FAA Form 7460-1 filing or the supplemental notice after the structure tops out. Coordinates from a hand-held GPS are not acceptable on the form.
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What a 1A or 2C certification letter is, and who asks you for one
Before you build or raise anything tall near an airport, or anything more than 200 feet above ground anywhere, 14 CFR Part 77 makes you tell the FAA about it on Form 7460-1, Notice of Proposed Construction or Alteration. The FAA studies the filing and issues a determination. The numbers it studies are yours: the latitude and longitude, the ground elevation above mean sea level, the height above ground and the overall height. A 1A or 2C letter is a licensed surveyor signing and sealing those numbers and stating how accurate they are.
The label comes straight from the FAA's obstacle accuracy codes. The digit is the horizontal tolerance and the letter is the vertical one, so 1A means plus or minus 20 feet horizontally and 3 feet vertically, and 2C means plus or minus 50 feet and 20 feet. The instructions on Form 7460-1 ask you to attach, if available, "a copy of a documented site survey with the surveyor's certification stating the amount of vertical and horizontal accuracy in feet." That certification is the letter.
The people who buy these surveys are not homeowners. They are tower developers and site acquisition firms filing new sites, carriers adding antennas that raise an existing structure, wind and solar developers with met towers and transmission structures, general contractors and crane companies who need a determination for a crane near a runway, and airport tenants building on airport property. In each case there is a filing date or an FAA condition behind the request, and the survey sits on the critical path.
FAA accuracy codes: what 1A, 2C and 4D actually certify
The FAA stores every verified obstacle with a two-part accuracy code. These are the tolerances published in the FAA's Daily Digital Obstacle File documentation (May 21, 2026 edition). The three combinations in bold type in the note below are the ones surveyors are asked to certify.
| Horizontal code | Horizontal tolerance | Vertical code | Vertical tolerance |
|---|---|---|---|
| 1 | plus or minus 20 ft | A | plus or minus 3 ft |
| 2 | plus or minus 50 ft | B | plus or minus 10 ft |
| 3 | plus or minus 100 ft | C | plus or minus 20 ft |
| 4 | plus or minus 250 ft | D | plus or minus 50 ft |
| 5 | plus or minus 500 ft | E | plus or minus 125 ft |
| 6 | plus or minus 1,000 ft | F | plus or minus 250 ft |
| 7 | plus or minus 1/2 nautical mile | G | plus or minus 500 ft |
| 8 | plus or minus 1 nautical mile | H | plus or minus 1,000 ft |
| 9 | Unknown | I | Unknown |
1A = 20 ft and 3 ft, the tightest code the FAA uses. 2C = 50 ft and 20 ft. 4D = 250 ft and 50 ft. Oklahoma City's airport publishes its on-airport "Certification of Data Accuracy" form with exactly those three boxes, and the surveyor ticks one, prints a registration number and state, and signs. If your determination or your client names a code, order that code. Ordering 2C when 1A was asked for means a second trip.
Do I need to file Form 7460-1? The notice triggers the survey has to support
Section 77.9 lists when notice is required. A surveyor is often the person who tells you which of these you trip, because the answer depends on measured distances and elevations, not on the address.
| Trigger | What the rule says | What the survey has to establish |
|---|---|---|
| Height | Any construction or alteration more than 200 ft above ground level at its site | Ground elevation and total height, including antennas, lights and lightning rods |
| Airport with a runway over 3,200 ft | Anything that exceeds a 100 to 1 slope for 20,000 ft from the nearest point of the nearest runway | Distance to the runway and the structure top elevation against the slope |
| Airport with a runway of 3,200 ft or less | A 50 to 1 slope for 10,000 ft from the nearest runway | Same measurement against the steeper surface |
| Heliport | A 25 to 1 slope for 5,000 ft from the nearest landing and takeoff area | Distance to the landing area and top elevation |
| Roads, railroads and waterways | The slopes above, after adding 17 ft for an Interstate, 15 ft for other public roads, 23 ft for a railroad | Road or track elevation where the traverse way crosses the surface |
| On-airport construction | Any construction on a public-use airport, a military or federal airport, or an airport or heliport with an instrument approach | Coordinates and heights on the airport datum, usually on the airport's own certification form |
| FAA request | Notice whenever the FAA asks for it | Whatever the FAA letter specifies |
Section 77.9(e) exempts a few things, including objects shielded by existing structures of equal or greater height in a congested area and antenna structures of 20 ft or less that do not add height to another structure. Timing is in section 77.7: file at least 45 days before construction starts or before you apply for a construction permit, whichever is earlier, and if the structure also needs an FCC license, no later than the date you file with the FCC.
"I can pull the coordinates off my phone": why the FAA rejects that
This is the most expensive shortcut in the process. The Form 7460-1 instructions say it in capitals: latitude and longitude derived solely from a hand-held GPS instrument is NOT acceptable, because a hand-held GPS is only accurate to within 100 meters (328 feet) 95 percent of the time. That is worse than the 250 foot tolerance of code 4D, never mind 1A. A filing built on phone coordinates can get studied on the wrong spot, and fixing it later means a corrected filing and a new study.
The form is also specific about the numbers. Coordinates go to the nearest second, or the nearest hundredth of a second if known, and the datum has to be stated (NAD 83 is preferred). Site elevation is in whole feet above mean sea level, rounded to the nearest foot. Structure height is rounded up to the next whole foot and must include everything mounted on top: antennas, obstruction lights and lightning rods. The overall height above mean sea level is the site elevation plus the structure height. A surveyor who does this work regularly delivers those values already formatted for the form, which is part of what you are paying for.
One more distinction trips people up. A 1A letter certifies accuracy; it does not certify that the FAA will approve anything. The FAA issues a Determination of No Hazard or a Determination of Hazard after its study. A no-hazard determination can carry conditions, marking and lighting recommendations and a supplemental notice requirement, and those conditions are often where a second survey is required.
The deadlines around an FAA survey, and when the second letter is due
Most projects need the surveyor twice: once for the proposed coordinates before filing, and once when the structure reaches its final height. Book both when you hire, because the second one is on a five day clock.
| Event | Deadline | Source |
|---|---|---|
| File Form 7460-1 | At least 45 days before construction starts or the permit application, whichever is earlier | 14 CFR 77.7(b) |
| Structure also licensed by the FCC | File with the FAA on or before the day you file with the FCC | 14 CFR 77.7(c) |
| Determination takes effect | On issuance, or 40 days after issuance if it is subject to discretionary review | 14 CFR 77.33(a) |
| Determination of No Hazard expires | 18 months after the effective date unless extended, revised or terminated | 14 CFR 77.33(b) |
| Supplemental notice after construction | Within the time set in the determination, or within 5 days after the structure reaches its greatest height | 14 CFR 77.11(b) |
| Project abandoned, dismantled or destroyed | Notice within 5 days | 14 CFR 77.11(c) and (d) |
Supplemental notice is mandatory for anything more than 200 ft above ground or whenever the FAA asks for it (section 77.11(a)). The as-built survey that supports it is the same measurement as the first letter, taken on the finished structure. If a 1A was requested, the as-built has to meet 1A too.
What to send surveyors so every FAA 1A quote prices the same job
There is no public price list for these letters. We looked, and none of the firms that sell them publish one, so the only way to know the price is to get it quoted. These eight lines make the quotes comparable.
- The accuracy code you need. 1A, 2C or 4D, and who set it: the FAA determination, the carrier, the tower owner or the airport. If nobody has said, ask before you order.
- Proposed or existing. A proposed site is surveyed at the ground (center of the future structure and ground elevation). An existing structure needs its top measured, which takes more equipment and time.
- The structure and its height. Monopole, guyed or self-support tower, rooftop antenna, building, crane, wind turbine, transmission line. For lines, every support has to be reported.
- The aeronautical study number, if a filing already exists, plus the determination letter if one was issued. The surveyor can read the conditions directly.
- The datum you file in. NAD 83 horizontal is preferred on the form; airports often want NAVD 88 elevations on their own certification form.
- Site access. Gate codes, landlord contacts, rooftop access rules, escort requirements, and for airports any badging or airside escort.
- The deadline and what drives it. A filing date tied to an FCC application, a crane pick date, or the five day supplemental notice window.
- Whether you need anything else from the same visit. A lease exhibit, a boundary or an access easement survey for the site is often cheaper done on the same mobilization.
How an FAA 1A survey runs, from request to sealed letter
1.
Scope and control research
The surveyor confirms the code, the structure and the datum, and finds published control near the site, such as NGS marks or a CORS network, that can carry the required accuracy.
2.
Field work
For a proposed site the crew locates the structure center and measures ground elevation with survey-grade GNSS. For an existing structure they also measure the top, usually by trigonometric methods from two or more setups.
3.
Reduction and check
Observations are processed and checked against the tolerance being certified. Height is rounded up and site elevation rounded to the nearest foot, as the form requires.
4.
Letter or form
You receive a signed and sealed certification letter, or the airport's own certification form completed and sealed, with coordinates, datum, site elevation, height above ground and overall height.
5.
Filing and follow-up
You or your filing consultant attach the letter to the 7460-1. When the structure tops out, the same firm returns for the as-built letter behind the supplemental notice.
FAA 1A survey questions
What is an FAA 1A survey?
It is a survey by a licensed land surveyor certifying a structure's coordinates, ground elevation and height to FAA accuracy code 1A: within 20 feet horizontally and 3 feet vertically. The sealed letter supports a Form 7460-1 filing or the supplemental notice after construction, and it is the tightest accuracy code the FAA uses for obstacles.
What is a 2C survey?
A 2C survey certifies the same values to FAA accuracy code 2C, which is within 50 feet horizontally and 20 feet vertically. It is looser than 1A and often enough for a proposed site well away from an airport, but order the code your determination or client asks for, because a 2C letter does not satisfy a 1A requirement.
How much does an FAA 1A survey cost?
There is no public price list; the firms that sell these letters quote each site. The price moves with whether the structure exists (measuring a tower top costs more than a ground point), the distance to usable control, access and escort rules, and the deadline. Send the same eight details to three licensed surveyors and compare flat quotes for the letter.
Who can certify a 1A letter?
A land surveyor licensed in the state where the structure stands. The certification form used on airport projects asks for the surveyor's printed name, registration number and state, signature and firm, and the letter is sealed. A filing consultant or engineer can prepare the 7460-1, but the accuracy statement comes from the surveyor.
Can I use my phone or a hand-held GPS for Form 7460-1?
No. The Form 7460-1 instructions state that latitude and longitude derived solely from a hand-held GPS are not acceptable, because such a unit is only accurate to about 100 meters (328 feet) 95 percent of the time. Use surveyed coordinates stated in a known datum, preferably NAD 83.
Does a crane need an FAA 1A survey?
A crane needs FAA notice when it trips a section 77.9 trigger, such as the slope surfaces around a nearby airport, and the Form 7460-1 asks how long a temporary structure will be up. Whether the FAA or the airport also asks for a surveyed accuracy certification depends on the site; check the determination and the airport's requirements before the pick date.
How long is an FAA determination good for?
A Determination of No Hazard to Air Navigation expires 18 months after its effective date unless it is extended, revised or terminated, under 14 CFR 77.33(b). If construction slips past that date, you may need an extension, and possibly updated survey data.
Is a Texas Category 1A survey the same as an FAA 1A survey?
No. In Texas, "Category 1A" is a land title survey class in the Texas Society of Professional Surveyors Manual of Practice, used in real estate closings. It has nothing to do with FAA obstacle accuracy. If you need a Texas title survey, see our ALTA and land title survey page instead.
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