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Airspace & Weather minimums

From looking at the areas people select to practice on PrepareToTest, rules and regulations get the most attention. Whilst its perhaps not as ‘exciting’ as learning about navigation or how the aircraft systems work, learning and understanding the various FAA regulations is a critical part of passing the knowledge tests and more importantly, being safe in the air. A question from yesterday’s Sport Pilot quiz highlighted one of topics that isn’t difficult but requires a bit of memorization to make it stick – weather minimums in different classes of airspace.

The question was as follows:

Light Sport Pilot Question: 0205_15

During operations within Class E airspace at altitudes of less than 1,200 feet AGL, the minimum horizontal distance from clouds requirement for flight is:
A – 500 feet
B – 1000 feet
C – 2000 feet

The correct answer is C. During operations within Class E airspace at altitudes of less than 1,200 feet AGL, the minimum horizontal distance from clouds requirement for flight is 2000 feet. Answer A is incorrect because 500 feet is the minimum distance below clouds in Class E airspace at altitudes of less than 1,200 feet AGL. Answer B is incorrect because 1000 feet is the minimum distance above clouds in Class E airspace at altitudes of less than 1,200 feet AGL. My first CFI taught me a useful memory aid for this common set of distances – 2 1/5, read as ‘two and one fifth’, the ‘one fifth’ is written as a fraction with the 1 above the line and the 5 below the line. 2 corresponds to 2000 feet horizontal visibility, 1 (above the line) corresponds to 1000 feet clearance above clouds, 5 (below the line) corresponds to 500 feet below clouds. This can be extended to ’32 1/5′ (“thirty two and one fifth”)for the common VFR visibility and cloud clearance minimums: 3 sm visibility, 2000′ horizontal, 1000 feet above clouds, 500 feet below clouds.

There are a lot of different permutations of airspace, height above ground, VFR or IFR, night or day. In searching around for some good online resources I found the AOPA Air Safety Foundation document “Airspace for Everyone” (PDF) that gives a very clear explanation of the various types of airspace including not only the main classes (A,B,C,D,E and G) but also special use airspace, restricted areas, military training routes and also the more recent phenomenon of Temporary Flight Restrictions (TFRs).

The ASF document also has some useful diagrams showing airspace and the various visibility and weather minimums which I have included below. These are great to use when learning about airspace and also to pack into your flight bag for quick reference when you need to confirm some facts before or during a flight. I liked their memory aid for class G airspace- “Class G, Government Free!”

If you want to check up on the gory details, you can find much more information on Airspace in FAR Part 71 – “Designation of class A, B, C, D, and E airspace areas”. For a slightly more user friendly description of this complex subject have a look at Chapter 3 of the Aeronatical Information Manual (AIM).

Airspace at a glance - Diagram from AOPA
Airspace Communications and Weather minimums

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