[ADXA] Tower restrictions near airports

[James Ferguson]

EJ,

I will get you more if needed but this should answer your question:

Here’s what the FAA part actually states, keeping in mind an antenna tower is “a construction or alteration:”

Any construction or alteration that exceeds an imaginary surface extending outward and upward at any of the following slopes:

(1) 100 to 1 for a horizontal distance of 20,000 ft. from the nearest point of the nearest runway of each airport described in paragraph (d) of this section with its longest runway more than 3,200 ft. in actual length, excluding heliports.

(2) 50 to 1 for a horizontal distance of 10,000 ft. from the nearest point of the nearest runway of each airport described in paragraph (d) of this section with its longest runway no more than 3,200 ft. in actual length, excluding heliports.

(3) 25 to 1 for a horizontal distance of 5,000 ft. from the nearest point of the nearest landing and takeoff area of each heliport described in paragraph (d) of this section.

The graphic below illustrates an example of a station one mile from a longer runway (>3200 feet) and a station one mile from a shorter runway (<3200 feet). Essentially, the antenna tower must rise no more than 1/100 the distance from the tower to the nearest edge of the runway if the runway is greater than 3200 feet long. If the runway is 3200 feet or less, the tower height may extend up to 1/50 the distance to the nearest edge of the runway.


Of course, the reason for the 20,000 feet (3.79 miles) horizontal range within which this calculation must be considered for a longer runway is due to the general location maximum allowable height of an amateur radio antenna structure without notifying the FAA and registering with the FCC… our question of interest.

When you are 20,000 feet from the nearest runway edge your tower may rise to 20,000 x 0.01 = 200 feet.  Similarly, for the shorter runway case, if you are 10,000 feet from the runway the tower may rise 10,000 x 0.02 = 200 feet.

With a heliport, the slope defining the maximum antenna height is 25:1, or the antenna may be 1/25 of the distance to the nearest edge of the heliport. At exactly the 5000 feet distance within which this must be considered, the antenna may again rise up to 200 feet high.

So, if you’re not near the airport, 200 feet is your limit without getting entangled in government red tape. If you are near the airport, get out your measuring tape and calculator.

> On Nov 30, 2022, at 3:39 PM, EJ Jones <k5ej at outlook.com> wrote:
> 
> Does anybody know the restrictions on tower height within 4 miles of an airport? Thanks.
> 
> EJ
> 
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