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See the attached diagram snippet for KRHV in Northern California. The chart supplement says that when the tower is closed the airport surface is class G. At this time, what is the floor of class E in areas "1" and "2"?

As you can see, class E starts at the surface around the Fairgrounds visual reporting point. Class E starts at 700 ft. AGL South-West of the airport and at 1,200 ft. AGL North-East of the airport. What happens in the middle in areas "1" and "2"? Does the magenta vignette cut through class D as shown by the red line or follows the border of class D? Again, this question is only relevant when the tower is closed.

enter image description here

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  • $\begingroup$ Have you checked the chart supplements for KRHV? It reads "AIRSPACE: CLASS D svc 1500–0600Z‡; other times CLASS G" which might answer your question. $\endgroup$ – svoop Mar 14 at 19:30
  • $\begingroup$ @svoop, he stated this much in the question. He wants to know where the top of the G, or bottom of the E is. $\endgroup$ – Michael Hall Mar 14 at 19:38
  • $\begingroup$ P.S. I don't know enough to answer, but I think your presumption about the red line you drew makes sense. Because D goes away, so too should its border... $\endgroup$ – Michael Hall Mar 14 at 19:50
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Short answer:

When looking at the airspace depiction on the sectional chart, it is logical to assume that the linear portion of the edge of the transition area with 700' floor, shown by the shaded magenta boundary, continues on through the blue segmented circle around KRHV, and this controls the floor of the Class E airspace in that area when the tower is closed and the Class D airspace reverts to Class G. In that case, the Class E floor in area "1" is 1200' AGL and the Class E floor in area "2" is 700' AGL. Similarly, it is logical to assume that the arcing circular edge of the 700'-floor transition area located north of KRHV also continues into the blue segmented circle around KRHV, but this section just barely extends into the blue segmented circle before it is intercepted by the linear edge of the 700'-floor transition area coming up from the southeast.

Long answer:

(Click here for a larger view of sectional chart centered on area of interest)

The ultimate authority for the answer to your question is found in the FAA's "Airspace Designations and Reporting Points" document, current edition Order JO 7400.11D. The class D airspace for KRHV is described on page D-156 under the heading "AWP CA D San Jose Reid-Hillview Airport, CA". No corresponding E2 airspace is listed-- it would be on page E-134 if it were present. This confirms what we read in the Chart Supplement-- that the Class D airspace for KRHV reverts to Class G, not Class-E-to-surface, when the tower is closed. The only exception is the small slice of airspace centered around the "6:30" position of the segmented blue circle around KRHV which does revert to Class-E-to-Surface when the Class D is inactive-- because it is part of an E3 "extension" associated with San Jose International (page E-153).

The magenta shaded border projecting southeast from the word "Evergreen" on the chart is the eastern edge of a "transition area" whose floor is 700' AGL, and your question is essentially asking whether this edge extends on into the segmented blue circle around KRHV, or deviates to include the entire segmented blue circle, or deviates in some other way. Transition areas are "E5" airspace, and are described starting on page E-220 in the "Airspace Designations and Reporting Points" document. The specific transition area we are interested in is described on pages E-960 through E-961, under the heading "AWP CA E5 San Jose, CA, San Jose International Airport, CA". When reading this text, it is helpful to know that "San Martin Airport" (KE16) was formerly known as "South County Airport of Santa Clara County".

Here is the complete text of the E5 airspace description, with the relevant portion highlighted:

That airspace extending upward from 700 feet above the surface within a 5-mile radius of the San Jose International Airport and within 4.3 miles each side of the NAS Moffett Field TACAN 157° radial extending from the NAS Moffett Field TACAN to 20 miles southeast of the TACAN and within 4 miles each side of the 139° bearing from the San Jose NDB, extending from the 5-mile radius of the San Jose International Airport to 24.3 miles southeast of the NDB and within a 6.9-mile radius of the South County Airport of Santa Clara County and that airspace bounded by a line beginning at lat. 37°30'00"N, long. 121°52'04"W; to lat. 37°22'00"N, long. 122°08'04"W; to lat. 37°22'00"N, long.122°24'04"W ; to lat. 37°30'00"N, long. 122°27'04"W, thence to the point of beginning. That airspace extending upward from 1,200 feet above the surface bounded on the north by lat. 37°30'00"N, on the east and northeast by long. 121°50'04"W; and the southwest edge of V-107, on the southeast and south by the northwest edge of V-111, and lat. 37°00'00"N, and on the west by the east edge of V-27 to lat. 37°30'00"N.

The 8-mile-wide strip of 700'-floor E5 airspace that extends 24 miles to the southeast of the San Jose NDB comes all the way up to the 5-mile-radius arc around San Jose International, and does not deviate either to avoid, or to completely include, the airspace enclosed by blue segmented circle around KRHV. Likewise the curving edge of the 5-mile-radius-circle of 700'-floor E5 airspace around San Jose International continues a short ways into the blue segmented circle around KRHV, before it meets the linear edge of the 700'-floor E5 airspace coming up from the southeast. So the edge of the 700'-floor E5 "transition area" does indeed run through the blue segmented circle around KRHV much as was sketched in the question. Area "1" is outside the 700'-floor E5 transition area and has a Class E floor at 1200' AGL when the Class D airspace is inactive, while area "2" is inside the 700'-floor E5 transition area and has a Class E floor at 700' AGL when the Class D airspace is inactive.

This answer has followed the common practice of referring to E5 airspace with a 700' Class E floor as a "transition area". This appears not to be actually supported by any current FAR or FAA document, including the "Airspace Designations and Reporting Points" document. "Transition area" is a term from before the 1993 "alphabet" airspace re-organization, and actually included areas that had controlled airspace floors at 1200' AGL as well as at 700' AGL. It is an obsolete term now, but still is often used by pilots, most commonly to refer to areas that have Class E floors at 700' AGL. At any rate, note that area "1" is actually still inside the airspace that is defined as part of the E5 airspace associated with San Jose International-- specifically, it is inside the portion of the E5 airspace associated with San Jose International that has a 1200' AGL floor. This answer does not intend to imply that there is some definitive reason to say that area "2" is inside a "transition area" while area "1" is not inside any "transition area". The main point of this answer is simply that when the Class D airspace around KRHV is inactive, area "2" has a 700' AGL Class E floor while area "1" has a 1200' AGL Class E floor.

Note that the "Airspace Designations and Reporting Points" document uses nautical miles and true bearings. A bearing of 139 degrees true is approximately 126 degrees magnetic at this location.

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  • $\begingroup$ This answer could be completely worked to avoid the use of the phrase "transition area", and substitute the phrase "700'-AGL-floor E5 airspace area" or similar. Not sure whether that would really be an improvement. $\endgroup$ – quiet flyer Mar 17 at 3:00
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The Class E transition area appears to be protecting the IAPs for RWY30L&R of KSJC. So, area #1 would be at 1200 AGL. Area #2 would be at 700 AGL. Considering the MEFs of the surrounding areas range from 3200 MSL to 4800 MSL, it may be a necessary precaution to separate the IFR traffic from the nearby Class G at the surface VFR traffic of E16.

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  • $\begingroup$ Did you mean 1200' instead of 1500'? $\endgroup$ – quiet flyer Mar 15 at 17:49
  • $\begingroup$ @quietflyer - Yes, I did. Thanks for the catch. $\endgroup$ – Dean F. Mar 15 at 22:58

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