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Airspace question


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Since we have had a few topics about different airspaces, I am going to add a question. What is the reason for having some airspaces measured in AGL and others in MSL? The only thing I can guess is that it has to do with higher elevations...but I can not find anything in writing that specifies the true reasoning...

 

Anybody know?

:mellow:

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Some airspace needs to be defined by MSL and some needs to be defined by the underlying terrain.

For example, Class E floors are defined by AGL (the underlying terrain)...it would be silly to define this airspace by MSL, or would it? In some areas, usually mountainous, the Class E has a uniform floor defined by MSL (see the zipper lines on a sectional).

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That's correct... It doesn't make a whole lot of sense to make the floor of Class E airspace 5000MSL when your airport is at 7000ft MSL. Then all airports above 5000MSL will have to meet the requirements of a Class E airport (Controlled) even if they have very very minimal funding for equipment. Not to mention the requirements for radar coverage in controlled airspace.

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For a surface area, the airport has to have both an instrument approach and weather reporting. For down to 700', just an instrument approach. Almost all the US has Class E down to 1200'.

 

An airport with a Class E surface area is uncontrolled. Controlled airports have Class B, C, or D airspace, although some revert to Class E when the tower is closed. The difference between a Class E and Class G airport is that you have to have a clearance to operate in the Class E when the weather is below basic VFR.

Edited by Gomer Pylot
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Don't forget, most Class D airports revert to Class G when the tower is closed unless they have the appropriate weather reporting, and even then I don't think they all do. Best bet is to check the AFD if you are unsure. Just wanted to clarify on what Gomer already said.

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For a surface area, the airport has to have both an instrument approach and weather reporting. For down to 700', just an instrument approach. Almost all the US has Class E down to 1200'.

 

An airport with a Class E surface area is uncontrolled. Controlled airports have Class B, C, or D airspace, although some revert to Class E when the tower is closed. The difference between a Class E and Class G airport is that you have to have a clearance to operate in the Class E when the weather is below basic VFR.

 

If the glass G A.P. has an instrument approach and WX reporting but is not E to the surface, is it because they did not request to be made as such. IE it is not an automatic thing to be made E to the surface, or is it? If it is automatically made that way, then does a GPS instrument approach not count? I ask because KEUL is G but has an NDB and RNAV GPS approaches and AWOS.

I'm pretty sure I know the answer, but since you did not specify....... Thanks GP.

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An airport with a Class E surface area is uncontrolled. Controlled airports have Class B, C, or D airspace, although some revert to Class E when the tower is closed.

 

I'm under the impression that Class E surface area IS controlled airspace. Therefore you have ATC services available although it is "non-towered." That is why you can get a special VFR clearance with center or a nearby tracon.

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It's semantics, I guess. It's controlled airspace when IFR, but not a controlled airport. To be a controlled airport, it has to have a tower. In Class E airspace, no clearance is required as long as the weather is better than 1000/3.

 

Class E to the surface is not automatic. To have it, it must meet the requirements, but meeting the requirements does not automatically make it Class E. The FAA has to designate it as Class E. It's also possible for an airport with a tower to still be Class G, even when the tower is operating. It's not common, but it is possible, and I've seen it. The only way to know for sure is to check the charts and/or AFD.

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