You forgot to square - looks like you did Pi times the radius which is...well nothing. Or half the diameter of a circle technically. Pi times the radius squared for area.


37 mode C veils on Class B airports. The ring is 30-60NM around the primary, let's just say they're all 30 miles. That means each ring encompasses 2827 square miles. So it's a total of 104,599 sq miles.

Class C ring is 10NM. Area of that circle is 314.16 sq miles, times 80 airports 25,120 sq miles.

129,719 square miles for those class B veils and class C airports, 4.157% of the continental US.

Yes we measure some non-continental US airports, but also assumed only a 30NM ring for all mode C veils so we're acutally under the real number.

Keep in mind if you wanna go above 2500' AGL now you're in airspace where it's required.

I assume that when mode C became the law of the land there were conversation similar to this playing out in hangars across the country.

Rats! How embarassing! I was rushing between patients, missed a step!

Looks like my 5% was pretty good estimate. Again it is likely much less due to overlap.

Mountain Doctor wrote:I did the math...

About 37 Class B airports/Mode C veils. 3350 square miles.

About 80 Class C airports. 1200 square miles.

So 4,550 square miles of ADSB restriction.

There are 3.12 million square miles in the continental US.

That works out to .14%.

I can avoid the .14%.

It's actually likely much less than that as much of B overlaps with C.

My math skills are really suspect, but I think yours are, too.

A Mode C veil is a 30 nautical miles radius circle. Area of a circle is found with the formula pi x radius squared. So 3.1416 x 900 is roughly 2827 square nautical miles. 2827 x 37 Mode C veils = about 104,615 square nautical miles of Class B/Mode C veils.

Class C airports generally have 5 mile radius cores to 1200' AGL and 10 mile radius shelves from there to 4000' AGL. There are some variations. But the ADS-B Out requirement will be that you can't fly above them, just like now you can't without a transponder, If we assume that means that for practical purposes there are 80 Class C airports that have 10 nautical mile radii. 3.1416 x 100 is roughly 314 square nautical miles. 314 x 80 = about 25,100 square nautical miles.

That totals 129,715 square nautical miles which will require ADS-B Out.

There are roughly 3,532,000 square miles of US, according to the Census Bureau. Converting that to square nautical miles (1 square mile = 0.75512 square nautical miles), there are approximately 2,667,000 square nautical miles.

That means that there is just under 5% (4.86%) of the total land mass of the US which will require ADS-B Out, except for those who fly above 10,000' MSL, which also requires it.

What that really means is that you and I have way too little to do, that we could waste our time making such pedantic calculations! I really should have gone flying instead, it's such a nice day!

Cary

What that really means is that you and I have way too little to do, that we could waste our time making such pedantic calculations! I really should have gone flying instead, it's such a nice day!

Amen Brother.

Clear skies and tailwinds.

Mountain Doctor wrote:Rats! How embarassing! I was rushing between patients, missed a step!

Looks like my 5% was pretty good estimate. Again it is likely much less due to overlap.

Math in public. no worries. you're saving lives, i'm sitting reserve. which one of us has stupid amount of time on their hands? ha!

Cary wrote:That means that there is just under 5% (4.86%) of the total land mass of the US which will require ADS-B Out, except for those who fly above 10,000' MSL, which also requires it.

This number seems pretty small, right? Unfortunately it lends one to assume an even distribution of required spaces. "5%? Hell, don't equip and just fly around it!"

Unfortunately there's local densities that can really ignore that global average depending on where you live, like Cary near Denver. Shoot, I live two miles from a Class C shelf and my plane is based out of that airport. I don't have a choice to equip or not, since I can't move (work) and the uncontrolled airports near me have an ~8 year waiting list for hangars.

Radar coverage has never been a deterrent to those who fly low. In transponder equipped aircraft there was an on/off switch. I assume there will be an on/off switch with GPS.

The government generally wants the assets and mainly the money to control everything. That doesn't mean they want to make the tremendous and unpopular effort to control everything.

For Mountain Doctor and myself it is really not an issue, other than expense. I rent both airplane and instructor now. I avoid areas where the switch might be necessary, mostly up, as in Cam's case. I will get along just fine until I check out. I won't hit you unless you are very low. Around the airport you will not see me because I will be low and waiting until you land.

Yes, the few of us down there have to see and avoid each other.

StampCreek wrote:....Keep in mind if you wanna go above 2500' AGL now you're in airspace where it's required....

Not quite correct, as I understand it.
ADS-B is required above 10,000' MSL, except within 2500' AGL.
So let's say you're at 15,000' MSL crossing the rockies--
ADS/B is not required if you are not more than 2500' above the terrain.

hotrod180 wrote:

StampCreek wrote:....Keep in mind if you wanna go above 2500' AGL now you're in airspace where it's required....

Not quite correct, as I understand it.
ADS-B is required above 10,000' MSL, except within 2500' AGL.
So let's say you're at 15,000' MSL crossing the rockies--
ADS/B is not required if you are not more than 2500' above the terrain.

Yup you're right. i was thinking all Class E airspace but it's as you describe. Thanks.

I think the confusion there is that if you have it installed it has to be ON in class A through E airspace. I'm pretty sure you can turn it off in G, though.

CamTom12 wrote:I think the confusion there is that if you have it installed it has to be ON in class A through E airspace. I'm pretty sure you can turn it off in G, though.

The rule regarding transponders is that if you have it installed and it works, it has to be on in flight, regardless of airspace. There's no option to turn it off legally. Since all of the 1090 installations involve transponders, either ES tied to an existing authorized position source, or all-in-one with a built-in position source, then they (which includes me) have no legal option to turn theirs off. 978 installations may be different, and perhaps it's those that folks talk about when they say they can use "stealth" mode. I haven't looked that up.

But I have to ask, "why?" Why, having spent the money, would anyone want to turn off the safety benefits of having others, who are properly equipped, "see" your 978 signal? Why would you not want ATC to see you mo' bettah than radar alone?

Cary

Cary wrote:

CamTom12 wrote:I think the confusion there is that if you have it installed it has to be ON in class A through E airspace. I'm pretty sure you can turn it off in G, though.

The rule regarding transponders is that if you have it installed and it works, it has to be on in flight, regardless of airspace. There's no option to turn it off legally. Since all of the 1090 installations involve transponders, either ES tied to an existing authorized position source, or all-in-one with a built-in position source, then they (which includes me) have no legal option to turn theirs off. 978 installations may be different, and perhaps it's those that folks talk about when they say they can use "stealth" mode. I haven't looked that up.

But I have to ask, "why?" Why, having spent the money, would anyone want to turn off the safety benefits of having others, who are properly equipped, "see" your 978 signal? Why would you not want ATC to see you mo' bettah than radar alone?

Cary

Pretty sure the reg reads that it has to be on in flight in all controlled airspace. Which means it would be legal to turn off in all uncontrolled airspace (G).

§ 91.215 (c)

Like Cary said, if you have spent the money there is no reason to not use it. When at Ag Flight, my students asked me how they could get home for a visit without having to go around a lot of airspace. They were getting limited commercial and the only planes Billy Howell owned with radio where a C-150 for the PPL test and a Comanche for the CPL. I told them to just stay low and out of D and nobody would bother them. None had any problems.

CamTom12 wrote:...Pretty sure the reg reads that it has to be on in flight in all controlled airspace. Which means it would be legal to turn off in all uncontrolled airspace (G). § 91.215 (c)

91.215 references transponder systems.
91.225 is the FAR which applies to ADS-B systems.

https://www.law.cornell.edu/cfr/text/14/91.225

91.225(f) says:
"(f) Each person operating an aircraft equipped with ADS-B Out must operate this equipment in the transmit mode at all times."

Doesn't say anything about where or when, it just says "at all times".
Pretty darn cut & dried IMHO.

hotrod180 wrote:

CamTom12 wrote:...Pretty sure the reg reads that it has to be on in flight in all controlled airspace. Which means it would be legal to turn off in all uncontrolled airspace (G). § 91.215 (c)

91.215 references transponder systems.
91.225 is the FAR which applies to ADS-B systems.

https://www.law.cornell.edu/cfr/text/14/91.225

91.225(f) says:
"(f) Each person operating an aircraft equipped with ADS-B Out must operate this equipment in the transmit mode at all times."

Doesn't say anything about where or when, it just says "at all times".
Pretty darn cut & dried IMHO.

Nope, you're right. I hadn't seen that section yet and was assuming it fell in the transponder category. I should have read a little harder.

Thanks for the correction!

CamTom12 wrote:

Cary wrote:That means that there is just under 5% (4.86%) of the total land mass of the US which will require ADS-B Out, except for those who fly above 10,000' MSL, which also requires it.

This number seems pretty small, right? Unfortunately it lends one to assume an even distribution of required spaces. "5%? Hell, don't equip and just fly around it!"

Unfortunately there's local densities that can really ignore that global average depending on where you live, like Cary near Denver. Shoot, I live two miles from a Class C shelf and my plane is based out of that airport. I don't have a choice to equip or not, since I can't move (work) and the uncontrolled airports near me have an ~8 year waiting list for hangars.

If I was in your situation, I'd grudgingly equip too.

CamTom12 wrote:

Cary wrote:

CamTom12 wrote:I think the confusion there is that if you have it installed it has to be ON in class A through E airspace. I'm pretty sure you can turn it off in G, though.

The rule regarding transponders is that if you have it installed and it works, it has to be on in flight, regardless of airspace. There's no option to turn it off legally. Since all of the 1090 installations involve transponders, either ES tied to an existing authorized position source, or all-in-one with a built-in position source, then they (which includes me) have no legal option to turn theirs off. 978 installations may be different, and perhaps it's those that folks talk about when they say they can use "stealth" mode. I haven't looked that up.

But I have to ask, "why?" Why, having spent the money, would anyone want to turn off the safety benefits of having others, who are properly equipped, "see" your 978 signal? Why would you not want ATC to see you mo' bettah than radar alone?

Cary

Pretty sure the reg reads that it has to be on in flight in all controlled airspace. Which means it would be legal to turn off in all uncontrolled airspace (G).

§ 91.215 (c)

You're right--should have looked it up instead of going by my (often) faulty memory!

But that's for transponders. ADS-B Out is different, as Hotrod180 has just pointed out--if installed, they must be on at all times.

Cary

Cary wrote:But that's for transponders. ADS-B Out is different, as Hotrod180 has just pointed out--if installed, they must be on at all times.

Cary

Yup. And I personally agree with your earlier point - if you have tech on-board that reports your position to other aircraft and can see other reporting aircrafts’ position, why wouldn’t you leave it turned on?

But the title of the thread made me feel like some wanted to see about not being tracked.

CamTom12 wrote:I think the confusion there is that if you have it installed it has to be ON in class A through E airspace. I'm pretty sure you can turn it off in G, though.

I originally though it was only required to be used in Class C and B... which makes sense. I can play along with that. Nice in congested areas.

Now I was told if you have it, it has to be ON, all the time, period! This is total BS in my opinion. Is this not the case? Even if you can shut it off in G, I still don't like it one bit. (the you are required to have it on part, even in E). What is the reasoning behind that exactly? Where is the data to suggest it's necessary to have in class E?

A buddy of mine suggested that before long, whether it was the intent all along, or just something that will develop from this - we will at some point all be charged for using the airspace. This would be the way to do it.

I'm not going to lose too much sleep just yet on that thought... but that notion seems more likely as time goes on.

Two years ago, the FAA was looking at getting rid of anonymous mode functionality. Not that it really matters, because anyone with a Mode S already has been telling the world. I don't really think it matters really one way or the other. If the FAA were to take a different tone towards GA, they won't need ADS-b to help them any.

No work has really been done yet to look at the impacts on safety that ADS-b is supposed to bring yet. It will be interesting to see if it has any real impact on routing, costs, safety, or any of the other much advertised ballyhoo. If there are improvements in the stats, it would be interesting to see how the half billion invested by owners and the 20 some odd billion invested by the government look next to other changes to the NAS.