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Practice Question: (Refer to FAA-CT-8080-2G, Figure 21) There’s a cluster of towers 13 statute miles south of Minot Airport. What’s the height of the tallest tower?

(Refer to FAA-CT-8080-2G, Figure 21) There’s a cluster of towers 13 statute miles south of Minot Airport. What’s the height of the tallest tower?
A) 2,676 ft. MSL
B) 3,147 ft. MSL
C) 1,031 ft. AGL

The intention of this question is to test knowledge of:

  • Identifying how to use the Sectional Chart scale to go 13 miles due south of Minot Airport
  • Identifying the obstruction icons
  • Understanding the difference between MSL and (AGL)

Remember that all obstructions on a sectional chart show two heights – the MSL height and the AGL height. Part of the question is whether you understand the difference between MSL and AGL, the latter always represented in parentheses on a Sectional Chart when referring to these obstruction heights.

But I think the real confusion lies in what “cluster” of towers the FAA is referring to.

If we go south 13 miles from Minot airport, there are three different tower icons. While most reasonable people (including myself) would look at all three icons and select the tallest of the three, the FAA is reminding us in a poor / tricky way that the “cluster” of towers is only that one icon on the far right.

Minot Towers Figure 21

That’s because it’s not a single tower icon, but two towers in one, which is a “Group Obstruction” icon indicating a small cluster of towers.

So, knowing that, the answer has to be either 3,147 ft. MSL or 1,081 ft. AGL…both are the same height and represent the tallest tower in that group / cluster. We have to ignore the two other tower icons to the left / west.

The FAA does not consider the towers to the west of 3147 (1081) to be part of the “cluster.”

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