Does Class D airspace go BELOW airport elevation?

[wsalopek]

I know the sentence is "Class D airspace extends from the surface to 2500 AGL". And by "surface", well, that probably means the surface of the earth out to a 4-mile radius around the center of the airport.

But...

I can see where "surface" could mean "surface of the airport", meaning, that elevations BELOW the surface of the airport are NOT in the class D airspace.

I ask because I would like to fly near (2-4 miles away) Allegheny County airport (near Pittsburgh). The airport is situated on a higher elevation piece of land (it was the first paved runway in the U.S. BTW)...and most of the surrounding terrain/neighborhoods are BELOW the airport elevation...meaning...I could typically fly 100-200 feet AGL and be BELOW the surface of the airport.

Anyway, I know LAANC is coming soon (and will probably solve my problems...I hope), but...what do you guys think the definition of "surface' is? I can't find that definition on FAA websites, etc.

Thanks...

 

[sar104]

Surface means surface, not airport elevation.

 

[jeplane]

Surface means earth.
So even if the airport is on a plateau, the class D all round that airport would include the ground below the airport elevation.

Think about it: There is only class A-B-C-D-E-G. What airspace would you be below that elevation?

A? Nope starts at 18,000 feet
B? Nope, that's for big airport.
C? Nope, that for not that big of an airport but more than class D.
E? It couldn't be since it goes up to 700 AGL or 1200 AGL depending.
G? That too goes to 700 AGL. (or all the way to 12,500 depending)

So you are left with class D, which encompass all the earth all around that airport, with below elevation, or higher elevation actually when you are in the mountains, like Aspen, CO class D

 

[jeplane]

Since I mention Aspen, let's take a look....

The airport elevation is ? That's right 7838.
But take a look at the Aspen private airport in the NE corner. What's the elevation there? 8440.
Is it in the class D? you bet! it is in the blue dotted circle.

So what type of airspace is it from 8440 -7838? If you said class D, that would be correct, since it starts from the earth, and belongs to Aspen tower.

But what about the river that runs by the airport, and shown as a gray line. I know that it is lower than Aspen airport , you say...
Doesn't matter.
It starts from the river and up, and still belongs to Aspen tower.
And quite frankly, it is a shame, because the landing on short final of runway 15 in Aspen would make some beautiful drone shots...

Ah well.

 

[wsalopek]

Thanks.

Yeah... I hear you guys... I figured surface meant surface... I was just hoping that any airspace below airport elevation would be uncontrolled, as really, what aircraft would be flying below airport elevation, esp within 4 miles of the airport?

Ok...a helicopter? Well...still...for the benefit of ALL airspace users, I vote for altitudes below airport elevation to be uncontrolled. after all, the Class D airspace would still be sterile as an aircraft would have to get approval to enter the class D airspace...from below.

Ah... If only my vote mattered.

 

[jeplane]

Maybe one day, or rather a number of years like... a century from now?
Airspace was created and approved by congress at a time where UAS did not exist.
Logically, you are correct that it "should" be fine if a UAS would fly under the ridge of a towered airport.... But we are not there yet, not by a long shot.