Class D under Class C

DesertNomad

DesertNomad

Pattern Altitude
Joined
Jul 5, 2013
Messages
2,445
Location
Northern NV
Display Name
Display name:
DesertNomad
I have seen, when Class D sits under Class C, the blue box denoting the upper limit of Class D has a "-" in front of the number.

This is not the case at KMWC which sits under the KMKE outer shelf. So Class D airspace stops at 2200, and then it is class C to 4700'. Why does the blue box for the Class D not say -32?

Same in California at KSAC where class D goes to 2500 but the Class C shelf starts at 1600, yet there is no "-" on the Class D altitude box.

At Monterey and Salinas (California) the D is listed as -25 and the C shelf starts at 2500.
 
Last edited:
When airspace overlaps the more restrictive applies, per 14 CFR 71.9. Class C is more restrictive than D, so the southwest corner of KMWC's Class D ends at 2199 and the Class C starts at 2200. There is no reason to make the Class D ceiling 3199 instead of 3200, it wouldn't change its relationship to the Class C at all, thus no minus sign.
 
Last edited:
I understand that Class C takes priority, so why is it listed as -25 at Monterey and Salinas? It would seem to mean the same thing with or without the minus sign since they stop/start at 2500.
 
DesertNomad said:
I understand that Class C takes priority, so why is it listed as -25 at Monterey and Salinas? It would seem to mean the same thing with or without the minus sign since they stop/start at 2500.
Click to expand...
KMWC goes up to 3200 with a notch cut out for the KMKE shelf at 2200. KSAC goes up to 2500 with a notch cut out for the KSMF shelf, which starts at 1600. The KMRY shelf starts from 2500 and underneath that is KSNS, which goes up to 2499.99999 with no notch. If KSNS didn't have the "-", it would need a .000001" notch
 
Ok. How many airplanes are 0.0000001" tall and could squeeze through the notch?

It just seems like without the minus sign, the more restrictive Class C would override any top of the underlying Class D. It is obvious that they touch each other with or without the minus sign. In other words, without the minus sign and at 2500' the Class C would take priority, even if your wheels were hanging into the Delta.

:)
 
Last edited:
DesertNomad said:
It just seems like without the minus sign, the more restrictive Class C would override any top of the underlying Class D. It is obvious that they touch each other with or without the minus sign. In other words, without the minus sign and at 2500' the Class C would take priority, even if your wheels were hanging into the Delta.
Click to expand...

The airspace dimensions are federal regulation, and have to go through the NPRM process. The variety of ways the FAA handles overlaps (sometimes explicitly, other times implicitly) is probably a result of different airspaces coming into existence at different points in time. It would be silly to create a new Class D and intentionally have it overlap with more restrictive airspace that negates part of what you're creating.
 
Last edited:
DesertNomad said:
How many airplanes are 0.0000001" tall and could squeeze through the notch?
Click to expand...
That's the whole point. With the "-", there is no notch like there is in the other 2 cases. It's just a continuous 0.00000001" space. If there were no "-" then there would be a notch.
 
But the notch would be infinitely small. Without the -, it should be clear that the transition from D to C happens at 2500 and at 2500 you are in C. It's just a bizarre way of doing things, IMHO.

Climb and maintain 2499.999999999999999999.
 
DesertNomad said:
I have seen, when Class D sits under Class C, the blue box denoting the upper limit of Class D has a "-" in front of the number.

This is not the case at KMWC which sits under the KMKE outer shelf. So Class D airspace stops at 2200, and then it is class C to 4700'. Why does the blue box for the Class D not say -32?

Same in California at KSAC where class D goes to 2500 but the Class C shelf starts at 1600, yet there is no "-" on the Class D altitude box.

At Monterey and Salinas (California) the D is listed as -25 and the C shelf starts at 2500.
Click to expand...
If you wanna have some real fun with this, check out Palo Alto and Moffett, KPAO and KNUQ.
 
so, that 0.0000000000000000000000000000000001 airspace is class E?
 
dmspilot said:
When airspace overlaps the more restrictive applies, per 14 CFR 71.9. Class C is more restrictive than D, so the southwest corner of KMWC's Class D ends at 2199 and the Class C starts at 2200. There is no reason to make the Class D ceiling 3199 instead of 3200, it wouldn't change its relationship to the Class C at all, thus no minus sign.
Click to expand...
Yeah. In the Salinas KSNS one, the C bottom and the D top share a common altitude. Why the guy who wrote that one decided to do the -25 thing, who knows. It is unnecessary. I’d chalk it up to overthinking it.
 
Here's some Myrtle Beach action:

upload_2022-5-12_12-17-53.jpeg
 
Let me see if I can get my right main wheel into Class D, left wing into Class B and right wing into Class E. Then I can have fun with cloud clearances.
 
DesertNomad said:
Let me see if I can get my right main wheel into Class D, left wing into Class B and right wing into Class E. Then I can have fun with cloud clearances.
Click to expand...
Just keep the transponder antenna in Class G and you’re good.
 
DesertNomad said:
Let me see if I can get my right main wheel into Class D, left wing into Class B and right wing into Class E. Then I can have fun with cloud clearances.
Click to expand...
Hmm. Seeing as how there are some communication requirements here, maybe the location of your radio antennae might be pertinent.
 
You must log in or register to reply here.
Back
Top