Could someone explain the class E extension used with class D?

Question

Could someone explain the class E extension used with class D?

Answer 1

Class E airspace is controlled.  The reason this airspace is controlled in conjunction with class D is for instrument procedures.  If you take a look at the class E it will surround the published instrument approaches... the ILS approaches, GPS, VOR, NDB approaches, etc.  It gives controllers a way to control approaches outside of their D airspace on crappy days, but does not have to be controlled on VFR days.

Answer 2

While it's true that Class E airspace extensions are generally associated with instrument approaches, they do not give the controller any additional ability to "control approaches" as someone else has posted.

What those Class E extensions do is bring the floor of Class E airspace to the surface.  In Class G airspace (underlies most Class E airspace), the flight visibility and cloud clearance restrictions can be significantly reduced.  This would allow some types of VFR operations into airports where the actual weather conditions may be IFR.

When Class E extends to the surface, VFR operations are not allowed in IFR weather.  This essentially keeps VFR traffic away from certain airports with instrument approaches.

***Update***

MALUBI CANYON wrote that Class E does not extend to the surface and quoted 14 CFR 71.71.  While he is correct in that generally, class E does not extend to the surface, the question (I'm assuming) is regarding the dashed magenta lines which apear on sectional charts.  In those cases, Class E does extend to the surface and for the reasons I indicated in my initial answer.

Answer 3

FAR 71.71 (c): Class E does not extend down to the surface. It extends down to either 700 agl (when designated in conjunction with an airport for which an approved instrument approach procedure has been prescribed) or 1200 agl, as per the Reg.

The purpose of Class E when used in conjunction with Class D is largely to affect VFR minima. (Are you referring to the Class D airspace itself---to variations in the lateral limits of Class D? That is a different question.)

If you don't have a copy of the Regs handy, they are available online at faa.gov. Click on Regulations and then find Part 71.71(c).