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What is "Defense Area" on a VFR Sectional Chart? The words "DEFENSE AREA" (in all caps) appear all along the US/Mexico border in blue. It's the biggest text on the chart. Interestingly enough, the same words don't seem to be along the US/Canada border.

Someone on airliners.net said this:

You're correct, there is a difference between a ADIZ and a Defense Area. A defense area is an area established on non-federal lands located within the United States, its possessions or territories, for the purpose of safeguarding classified defense information or protecting government equipment and/or material.

The establishment of a national defense area temporarily places such non-federal lands under the effective control of the Department of Defense and results only from an emergency event.

I am surprised that it is charted though, unless of course the government is getting ready for the flood of illegals coming to California to get drivers licenses and registering to vote.

That makes it sound like a ground thing, not an air thing. Then there's this, in the CFR 99.3:

Unless designated as an ADIZ, a Defense Area is any airspace of the United States in which the control of aircraft is required for reasons of national security.

And in the CFR 99.49:

All airspace of the United States is designated as Defense Area except that airspace already designated as Air Defense Identification Zone.

And in the AIM:

Defense Area means any airspace of the contiguous U.S. that is not an ADIZ in which the control of aircraft is required for reasons of national security.

So, what exactly is this Defense Area on my Sectional Chart and do I need to worry about it or think about it as I fly?

From the CFR 99.3 quote, what does this mean?

in which the control of aircraft is required for reasons of national security

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    $\begingroup$ Which sectional chart are you referring to, and could you describe it or help talk my eyes onto what specific area you are looking at? I live in Washington state and fly off the Seattle sectional. We have a coastal ADIZ and the Canadian border, but I can't picture what you are asking. Thanks. $\endgroup$ Commented Jan 9, 2019 at 20:05
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    $\begingroup$ The term "defense area" doesn't appear in the FAA's Chart User's Guide. Can you give an actual example? $\endgroup$
    – Pondlife
    Commented Jan 10, 2019 at 2:30
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    $\begingroup$ Hey, Michael. I live in Tacoma. Go to SkyVector.com and look along the Texas/Mexico border. There are several instances of the words "DEFENSE AREA" all along the US/Mexico border. It's the biggest text on the chart and is blue. You really can't miss it. $\endgroup$
    – birdus
    Commented Jan 10, 2019 at 19:52
  • $\begingroup$ The FAR 99.49 quoted above was removed in 2004 and replaced by FAR 99.49 $\endgroup$
    – StephenS
    Commented Jan 11, 2019 at 2:56

2 Answers 2

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FAR 99.3 defines a Defense Area as an area in which air traffic can be controlled in the interest of national security. In other words, non-ADIZ airspace in which SCATANA or a similar plan can be implemented. In other words, all domestic airspace. It used to be clear that all airspace was Defense Area until FAR 99 got rewritten a couple of times in 2001-2004 when they were trying to figure out if the DC SFRA was an ADIZ. Now, the FAR that explicitly says that all non-ADIZ airspace is Defense Area is gone (to who knows where).

Nonetheless, all airspace that isn't an ADIZ is Defense Area, from sea to shining sea.

So why is it depicted on the southern border? To clarify that the airspace is not an ADIZ.

enter image description here

Take a look at this piece of the San Diego TAC. Notice how out in the ocean, the ADIZ is an actual 2-dimensional region. It's depicted with solid magenta lines with dots protecting the inside of the ADIZ. But at the beach, it devolves into a 1-dimensional line. But it's still depicted as the magenta line with dots. Look right there at the beach what has to happen, how the dots have to jump over the line. Thing is, since the ADIZ is a line there, the dots are actually outside of it, they can't protect the inside of it (since there is no inside to protect) and it looks like maybe all of California is an ADIZ, when it isn't. So the words DEFENSE AREA are printed there across the border from CONTIGUOUS US ADIZ to emphasize that the dots aren't actually protecting an ADIZ area; the ADIZ is too narrow to be correctly depicted.

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  • $\begingroup$ Great answer, thanks for confirming! $\endgroup$
    – novwhisky
    Commented Oct 17, 2022 at 12:14
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What is a Defense Area?

A "Defense Area" is any area entirely surrounded by an ADIZ but not part of that ADIZ. This is easier to understand with this older map:

Old ADIZ map

Here you can see the Western Defense Area surrounded by the Pacific ADIZ, (part of) the Northern ADIZ, the Western ADIZ and (part of) the Southern Border ADIZ. Likewise we can see the Eastern Defense Area surrounded by the Atlantic ADIZ, the Eastern ADIZ, (part of) the Northern ADIZ and (not shown) the Canadian ADIZ.

The Southern Border ADIZ was somewhat special (and challenging to chart) because it is zero-width, unlike the other ADIZes.

Notice that much of the Plains and Rockies are in the Central Open Area, which is not enclosed due to the lack of an ADIZ over the Gulf of Mexico.

In later years, there were several changes:

  1. The Pacific ADIZ, Southern Border ADIZ, a new Gulf of Mexico ADIZ, and the Atlantic ADIZ were merged together into the Contiguous US ADIZ.
  2. The Northern, Western, Eastern and Albuquerque ADIZes were eliminated.
  3. The Alaska ADIZ was created.
  4. The (eastern) Canada ADIZ was extended all the way from the East Coast around to Alaska.
  5. A short (western) Canada ADIZ was created from Washington state to Alaska.
  6. With ADIZes now completely encircling all of the Contiguous US, Canada and (most of) Alaska, that entire area became one big Defense Area, and the Central Open Area disappeared.

Note that the Alaska's western Aleutian Islands, Hawaii, Puerto Rico and various other island territories are not enclosed by an ADIZ and thus are still not part of a Defense Area.

What does this mean for pilots?

Aircraft crossing an ADIZ into a Defense Area are presumed hostile unless/until identified. This means they must be on an IFR or DVFR flight plan, squawking a discrete transponder code and in contact with ATC/FSS. If you are not, you will likely be intercepted by defense aircraft, either American or Canadian depending on which ADIZ it is, to ensure you're not a Soviet Russian bomber performing a sneak attack. This is the original purpose of North American Aerospace Defense Command (NORAD), and why there are Canadians permanently stationed on a US military base.

In contrast, aircraft flying entirely within or leaving a Defense Area are presumed friendly, and you won't be intercepted unless you give them a specific reason to think you're hostile. Reasons would include penetrating a Prohibited Area, a Restricted Area or the DC SFRA/FRZ without permission, or squawking 7500. As a result, if you're VFR, you don't need to talk to ATC/FSS in class E/G airspace or (at least in the US) file a VFR flight plan at all. Still, you should be aware of intercept procedures and monitor 121.5 if you're not talking to ATC/FSS, just in case.

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    $\begingroup$ How far away from the border does it extend? There are uncontrolled airports right on the border. What happens if you land there? "with slightly different rules" What rules? $\endgroup$
    – birdus
    Commented Jan 11, 2019 at 2:21
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    $\begingroup$ How can his plane be searched without a warrant? If he didn't land coming from another country, how do they justify it? What's their probable cause? $\endgroup$
    – birdus
    Commented Jan 11, 2019 at 3:07
  • $\begingroup$ @birdus FYI, I’ve replaced my answer as I’ve discovered the old one was incorrect. Please check it out and let me know if you have any questions. $\endgroup$
    – StephenS
    Commented Jan 3, 2022 at 16:54

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