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AGL and MSL on sectional charts, which?

samd012

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I am taking some sample test to see what I need to learn better and I have 3 questions that all tie together. Hoping someone can help

First there is a sectional chart that is showing an airport with a class E airspace circle around it. Would that be 700ft AGL or MSL for the floor of the class E space?

Then there is another sectional that asks what the floor is in the outer circle of a class C airport. Would that answer be 1300 AGL or MSL (the chart shows a 41 over 13 inside the outer solid magenta circle)?

I am being told the first is in AGL and the second is in MSL. Is that correct? And if so how do you know when to answer AGL vs MSL
 
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Whoever told you told you correct information.
The 700' is AGL and the 41/13 is MSL.

This kind of explains it:
How To Read A Sectional Chart

A little history here.
Back in the old days, before all this class nonsense, these areas used to have names. Airport traffic area, terminal control area, control zone etc.
They changed those to this letter class thing.
Control zones usually began at either 700' or 1200' AGL. That's what this airspace is, and its AGL.
 
Whoever told you told you correct information.
The 700' is AGL and the 41/13 is MSL.

This kind of explains it:
How To Read A Sectional Chart

A little history here.
Back in the old days, before all this class nonsense, these areas used to have names. Airport traffic area, terminal control area, control zone etc.
They changed those to this letter class thing.
Control zones usually began at either 700' or 1200' AGL. That's what this airspace is, and its AGL.


Thanks for the reply, I do understand that. What confuses me is the first answer about the class E space which they say is AGL, not MSL. I would think a sectional would always be MSL unless otherwise noted so why i sthat answer in AGL?
 
Kind of hard to explain, but the standard for getting IFR flights into controlled airspace when operating from airports without operating control towers was to begin that controlled airspace at either 700 or 1200 feet above the ground.
So when you see those magentas with either a 700 or 1200, the number is AGL.
One of the easiest ways to tell, if you forget, is to look at all the other elevation data close by, and there is always a lot of it. Those numbers are MSL, and you can tell that 700 must mean AGL, because it wouldn't make sense otherwise.
 
Kind of hard to explain, but the standard for getting IFR flights into controlled airspace when operating from airports without operating control towers was to begin that controlled airspace at either 700 or 1200 feet above the ground.
So when you see those magentas with either a 700 or 1200, the number is AGL.
One of the easiest ways to tell, if you forget, is to look at all the other elevation data close by, and there is always a lot of it. Those numbers are MSL, and you can tell that 700 must mean AGL, because it wouldn't make sense otherwise.

Ahhh, I think I understand. Tricky question then and I learned something. Thank you so much for the help
 
Whoever told you told you correct information.
The 700' is AGL and the 41/13 is MSL.

This kind of explains it:
How To Read A Sectional Chart

A little history here.
Back in the old days, before all this class nonsense, these areas used to have names. Airport traffic area, terminal control area, control zone etc.
They changed those to this letter class thing.
Control zones usually began at either 700' or 1200' AGL. That's what this airspace is, and its AGL.


So all Classes B-E are noted as AGL? Shelf, ceiling, everything? This distinction is kicking my arse too and I know it shouldn't be too difficult.
 
Class B starts at the surface.
The upper limit is MSL.

Now I'm more confused. Bare with me here:

Class B is the only class in MSL and the rest are in AGL?

Or all classes are AGL at the shelf and MSL at the ceiling? Sorry for being an idiot.
 
No problem. It is confusing.
Class B starts at the surface.
Understand that class B is only for the busiest airports in the US, and only 37 of them.
O'Hare, Atlanta, LA, Kennedy etc.
The controlled airspace starts at the surface, and generally extends to 10,000' AGL.
All air traffic within class B is controlled, and requires a clearance.

On a sectional chart, the altitudes depicted in the "inverse wedding cake" are MSL altitudes.
So, while the controlled airspace around the primary airport starts at the surface, the airspace has horizontal limits, and those are depicted on a sectional in MSL.
 
No problem. It is confusing.
Class B starts at the surface.
Understand that class B is only for the busiest airports in the US, and only 37 of them.
O'Hare, Atlanta, LA, Kennedy etc.
The controlled airspace starts at the surface, and generally extends to 10,000' AGL.
All air traffic within class B is controlled, and requires a clearance.

On a sectional chart, the altitudes depicted in the "inverse wedding cake" are MSL altitudes.
So, while the controlled airspace around the primary airport starts at the surface, the airspace has horizontal limits, and those are depicted on a sectional in MSL.

Class B aside, when will I know when to use AGL vs MSL? I know structures and terrain are depicted in both, so that's easy, big airspaces around airports are easy to figure out since it's the fraction-looking number. The questions on the practice tests that always get me are the ones that ask where, for example, Class C/D/E starts. Whenever I think it's MSL, it always happens to be AGL and vice versa. The human race is extremely lucky I don't fly manned aircraft!
 
This says that C and D are "charted" in MSL. https://www.faa.gov/regulations_policies/handbooks_manuals/aviation/phak/media/17_phak_ch15.pdf

So numbers you see for those are MSL numbers. E typically has no numbers, instead you look at whether it's a magenta broken line, magenta shading or blue shading.

From this same source: "In most areas, the Class E airspace base is 1,200 feet AGL. In many other areas, the Class E airspace base is either the surface or 700 feet AGL. Some Class E airspace begins at an MSL altitude depicted on the charts, instead of an AGL altitude.
Class E airspace typically extends up to, but not including, 18,000 feet MSL (the lower limit of Class A airspace). All airspace above FL 600 is Class E airspace."
 
Last edited:
As mentioned, but here are some pics with it-

Class B altitudes, MSL-

196D4A2C-E9F5-47AE-A79E-13CB64632DF4.jpeg



Class C, MSL-

50267E84-46A5-4FA8-8BF5-731E546C6371.jpeg

Class D, MSL-

BC4010BD-B0CC-4447-92DB-791739B79F46.jpeg

Class E, AGL-

FE95A839-DBCE-415F-9CCA-03835ECE1D30.jpeg

Class D, (MSL) with class E, (AGL)-

4A238019-EAAA-4987-9631-F5A2356E4216.jpeg

Class E to the surface-

C5661821-E3E2-4B94-8991-519BA16C3855.jpeg

Class E like that is typically to protect aircraft on an instrument approach.

Class E sometimes to the surface (as indicated by the note)-

E392CD6C-896E-45B7-A332-128E260AFF3E.jpeg
 

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