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A Class D airspace ceiling is typically depicted with a two digit number surrounded by four brackets depicted below. enter image description here

Why do some Class D airspaces have the same four brackets, with four additional lines within those bracket lines. I've checked the chart user guide and it shows an example of it but that example isn't consistent with airports across the US. Picture below. enter image description here

As you can see, where it says [32], there are only four right angles around it, whereas in the second example, where it says [62] there are four additional lines in between each right angle and I can't find an answer anywhere.

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  • $\begingroup$ Surely class D is just depicted with a number surrounded by a dashed line, and the number of line segments will depend on the zoom level? $\endgroup$
    – 60levelchange
    Nov 19 at 7:04
  • $\begingroup$ @60levelchange -- how do you zoom a paper chart? PS most on-line products you find are just digital copies of the paper charts, or at least of their actual map portions, i.e. some exclude the margins and the information contained therein. $\endgroup$
    – quiet flyer
    Nov 19 at 21:09

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The FAA's Chart User Guide clearly says "Class D Airspace is identified with a blue dashed line." on page 17, and on page 27 it shows examples with four and eight blue dashed segments. The eight segments example is used in a bigger box, the four segment example is used in a smaller box. No contradictions here, the text merely says "Class D Airspace is identified with a blue dashed line." which is clearly the case in both examples.

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  • $\begingroup$ Suggested edit-- something to the effect of "In general, bigger boxes are used in larger areas of Class D airspace, or when three characters need to be enclosed, e.g. when there is a "-" sign." $\endgroup$
    – quiet flyer
    Nov 19 at 21:13
  • $\begingroup$ @quietflyer: "larger areas of Class D airspace" would refer to the airspace itself. The four vs. eight segments question has nothing to do with the airspace size but with the sized of the displayed box. $\endgroup$
    – Andreas Lauschke
    Nov 20 at 7:40

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