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When did the thin dashed magenta line, currently used to illustrate Class-E-to-surface airspace, first appear on the legend of US VFR sectional charts? I'd like to narrow down the date as precisely as possible. Currently I'm aware that this marking DID appear on the legend of a sectional chart (Hawaiian Islands) effective November 12 1992, and did NOT appear on the legend of a sectional chart (Bethel Alaska) effective August 20 1992. Please post the "effective date" of any US VFR sectional chart that you are aware of before November 12 1992 in which the thin dashed magenta line does appear on the legend, or the "effective date" of any US VFR sectional chart that you aware of after August 20 1992 in which the thin magenta line does not appear on the legend.

Note that on the legend of the November 12 1992 chart, the thin dashed magenta line is identified not as depicting "Class E airspace", but rather as depicting "Control Zone at airport without control tower and Control Zone extension without communications requirement". The term "Class E" didn't show up on legend of US VFR sectional charts until 1993.

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  • $\begingroup$ all instances of "thin magenta line" should read "thin dashed magneta line" $\endgroup$
    – quiet flyer
    Commented Nov 1, 2018 at 10:58
  • $\begingroup$ It was in place in the US already when I started flying in April of 1994. But hadn't been for very long at that point. Long enough tho to make into the text books. $\endgroup$
    – CrossRoads
    Commented Nov 1, 2018 at 12:22
  • $\begingroup$ Re "Note that on the legend of the November 12 1992 chart, the thin dashed magenta line is identified ... as depicting "Control Zone at airport without control tower and Control Zone extension without communications requirement"." -- it's worth nothing that prior to September 16 1993 the boundaries shown by the dashed blue and magenta lines had nothing to do with communication requirements. Rather, if not in a TRSA etc, pilots had to communicate with control towers when within an "airport traffic area", which was a cylinder of airspace 5 statute miles in diameter, extending to 2000' AGL, $\endgroup$
    – quiet flyer
    Commented Jan 6, 2022 at 19:32
  • $\begingroup$ (ctd) surrounding all towered airports. Therefore the Nov 12 92 chart legend only makes sense when we realize that relatively few of the areas charted as Control Zone "extensions"-- which on Sept 16 1993 would be transformed into surface-level Class E "extensions" to Class D (or higher) airspace, a.k.a. E3/E3a/E4 airspaces-- extended closer than 5 statute miles to the airports whose approaches they protected. The main purpose of the "without communications requirement" phrase in the chart legend was actually to prepare pilots for the changes that would come on September 16, 1993. $\endgroup$
    – quiet flyer
    Commented Jan 6, 2022 at 19:36
  • $\begingroup$ This question, or perhaps one of the associated answers, would benefit from having this content integrated into it. $\endgroup$
    – quiet flyer
    Commented Jan 6, 2022 at 19:39

3 Answers 3

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The decision to change the airspace classification in the US to bring it into agreement with ICAO classifications was made in December 1991, as can be seen in the US Library of Congress: Federal Register: 56 Fed. Reg. 65415 (Dec. 17, 1991).

The ICAO classification was only used from the 16th of September 1993, but as part of the familiarisation process for pilots, the legends of the charts were already updated before.

The Federal Register (FR) contains a table with the Airspace Reclassification Transition timeline.

Airspace Reclassification Transition table

This table shows that as of October 15, 1992, the first sectional aeronautical charts (SAC), world aeronautical charts (WAC) and terminal aeronautical charts (TAC) are published with legends that indicate both existing and future airspace classifications.

Furthermore the FR specifies that it is anticipated that a segmented magenta line will be used for class E in the future, and that starting October 15, 1992, the new colours will be used in the legends.

An anticipated modification to the symbols on aeronautical charts is the addition of a segmented magenta line to represent the controlled airspace area for airports without operating control towers that extends upward from the surface (Class E airspace).

[....]

The legends in aeronautical charts will include both the existing airspace classifications and the airspace classifications to be effective September 16, 1993. For example, the solid blue line that symbolizes a TCA will be followed by "TCA (Class B)." The first charts with a dual legend will be published October 15, 1992. Commencing September 18, 1993, the legends on these charts will be reversed (e.g., a solid blue line will be followed by "Class B (TCA)". Between March 3 and August 17, 1994, the use of dual indication legends will be phased out.

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  • $\begingroup$ It does relate to it. I've added an additional relevant quote from the FR. $\endgroup$
    – DeltaLima ♦
    Commented Nov 1, 2018 at 16:32
  • $\begingroup$ Thank you for the added comment. It's interesting that as of now, I've seen charts with the dashed magenta line with the legend bearing the old terminology "Control Zone at airport without control tower and Control Zone extension without communications requirement", but none bearing the old terminology AND a reference to "Class E" airspace. $\endgroup$
    – quiet flyer
    Commented Nov 1, 2018 at 16:49
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According to this AOPA article, the change was made in Sept, 1993

In a move to simplify airspace classification, the FAA will rename the different airspace categories on Sept. 16, 1993. In order to fall in line with ICAO (International Civil Aviation Organization) practices, it will replace descriptive titles, such as Terminal Control Area, with alphabetical designators, such as Class B Airspace. This change will be phased in gradually. Charts and references will carry both designations until pilots get used to the transition.

https://www.aopa.org/members/ftmag/article.cfm?article=1054

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  • $\begingroup$ This was a good answer to the other related question, but doesn't really answer this question, as the appearance of the thin dashed magenta line preceded the "alphabet" reclassification, as stated in the question. $\endgroup$
    – quiet flyer
    Commented Nov 1, 2018 at 15:17
  • $\begingroup$ Why does it matter when? What are you looking to establish? $\endgroup$
    – CrossRoads
    Commented Nov 1, 2018 at 15:20
  • $\begingroup$ Oh, it's a little complicated. I'm trying to improve a part of my answer to another question, relating to how "control zones" evolved into their present form. $\endgroup$
    – quiet flyer
    Commented Nov 1, 2018 at 15:28
  • $\begingroup$ I thought that was just forced on us (in the US) by ICAO requirements. English is the universal language of aviation, I guess we can live with some ICAO nonsense. Has been 25 years, I don't really think about it when I fly, as it's always been Class A-B-C-D-E-G for me. I don't fly in A, my plane won't go that high. My home airport is near a B and under its C veil, so radio work is not an issue either. $\endgroup$
    – CrossRoads
    Commented Nov 1, 2018 at 15:35
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It appears from the content given in this related answer Re old (1992) US VFR sectional charts-- when was the thin dashed magenta line first used? that it was anticipated that the new markings (e.g. thin dashed magenta line) would be introduced on October 16 1992. So it is unlikely that the change was made before this date. Whether US VFR sectional charts ever actually contained legends using the older "Control Zone..." terminology and the newer "Class D", "Class E" terminology is not clear at this point. Also note the reference to a 28-day AIRAC cycle for issuing new batches of charts, in a comment by "DeltaLima" to this related question Re old (1993) US VFR sectional charts-- when did the term "Class E" first appear? :"The date will an AIRAC cycle date. Changes to airspace and procedures are only introduced on cycles of 28 days" As noted in the current question, we know that by Nov 12 the new markings had been introduced-- November 12 is the "effective date" of a sectional chart bearing the new markings . 28 days before November 12 is October 15, before the October 16 target date, so it seems that November 12 1992 may be the answer to the question. It would be good if someone could locate and check a sectional chart that became effective in mid-October 1992 (presumably October 15 1992) to confirm that the dashed magenta line is absent.

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