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9 Answers

Why are cloud clearance requirements reduced in Class B airspace?

Asked by: 10577 views ,
General Aviation

1) GENERALLY, in Classes C, D and E VFR...pilots need to remain 500 feet below/1000 feet above/2000 feet horizontally from the clouds.

However, in Class B airspace, pilots merely need to remain "clear of clouds."  This does not make sense to me.  It would seem that since Class B is very busy, ATC would want to keep VFR flights far as away from the clouds as possible. 

Since jetliners and IFR pilots are constantly popping in and out of the clouds, it seems a danger to have VFR flights simply remaining "clear of clouds" in an airspace as busy as Class Bravo.

What is the reasoning behind the reduction in cloud clearance requirements for Class B?

2) Are airports within Class E airspace always uncontrolled (non-towered)? 

3) Since Class D airspace reverts to Class E when the tower is closed...does Class C also revert D?  Or...are Class C towers always open?

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9 Answers



  1. Rodrop on Jan 30, 2011

    I suspect it has something to do with the fact that ATC is supposed to provide separation to all flights (VFR etc) not just IFR.  I think in C and down, that is not the case, it is not separation of all flights, it is separation based on IFR.    I may not be articulating it totally correct, but I think the key words are separation of ALL flights in the airspace.

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  2. John D. Collins on Jan 30, 2011

    It makes it much easier for VFR aircraft to fly in Class B airspace.  Since you are being separated from other traffic, you don’t have to worry as much about another airplane popping out of the clouds and having to avoid it.  For example, if the conditions are 10 miles and 3000 feet overcast, it is still easy to remain in visual conditions clear of the clouds.  It is easy for ATC as well, as they can vector you around traffic without as much worry about putting you near the clouds, still VFR but inside the lateral or vertical limits of VFR in other airspace.  You are usually given a clearance inside the Class B that limits you to VFR and assigns you an altitude and direction of flight, but if you are going to enter a cloud, you have to speak up so that ATC can change your course or altitude so you can remain clear of the clouds.
     

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  3. Wesley Beard on Jan 30, 2011

    To answer your second question. Yes. They are without towers.

    To answer the third question… Class C usually doesn’t close. There is only one Class C that I know of that vloses and that is Shaw AFB in South Carolina (KSSC). The A/FD for Shaw states the Class C is open on weekdays from 8am to Noon local time. Other times it is Class D. The sectional chart shows both classes of aitspace for Shaw.

    Class D doesn’t always revert to Class E when the tower closes. It sometimes goes to Class G. See KRN and KIWA to see what I mean. The AFD will give you that information.

    See runwayfinder.com or skyvector.com to view the sectional chart

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  4. Chuck Toussieng on Jan 30, 2011

    Howdy!
    Actually, it makes perfect sense!  The reason is that in Class B, you are provided what is known as “separation service” by ATC.  When you are inside Class B, ATC will keep you from bumping into someone else.  That is why you will normally hear a controller tell you to “stay clear of the (whatever) Class Bravo” you may get too close to, because they may not have the time to fit you into what’s going on.
    That is also one of the reasons you need to hear those magic words: “November-blah-blah is cleared through the blah-blah Class Bravo…”  That’s them letting you know, OK- we will keep a (closer) eye on you while you’re in here.
     
    Question #2: No.  As far as airports go, it’s always best to check the AFD and checkout your chart for tower info.
     
    Question #3: There are several Class C airports which have towers that close.  A super-busy one in SoCal is John Wayne- KSNA.  Usually, in my experience when a Class C tower closes, the Class C “goes away” and any E or G fills in.
    I don’t know how a Class C with a closed tower could become a Class D since Class D requires communication with the controlling tower- unless there is “another” tower at another nearby airport that becomes the controlling entity-  but to be safe always checkout the AFD.
    HAVE FUN!!
     
     

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  5. skyboyCFI on Jan 31, 2011

    [Why are cloud clearance requirements reduced in Class B airspace?]
    Because all the Bravo air traffic is under control by ATC. Seperation of aircraft is covered completely. All aircraft are in contact with the controlling agency under radar coverage.
    Outside of Bravo airspace, this is not the case. Class D & C do not always have radar. And of course, outside of Bravo, it’s nice to have a buffer when you’re flying 250+kts and pop out of a cloud.

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  6. VFR Student on Jan 31, 2011

    Meant to ask if Class C reverts to class “E” when the tower is closed.

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  7. Wesley Beard on Jan 31, 2011

    It really depends a lot on the airspace makeup.  Shaw AFB reverts to Class D because the TRACON closes and not the tower.  John Wayne Airport reverts to Class G when the tower is closed.  Eastern Iowa Airport (CID) Class C reverts to Class E when the tower closes.
     
    I don’t know why sometimes it reverts to Class E and sometimes it reverts to Class G when the tower closes.  I do know that to be absolutely sure what that airspace reverts to, you must consult the Airport Facilities Directory.

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  8. Matt Bowers on Feb 07, 2011

    Just adding to Mr. Toussieng’s thorough answer, that ATC has really good radar in Class B.  Also, besides having to get permission to enter, you are required to have a Mode-C or better transponder which gives ATC more accurate information.
    Side note: While flying south of San Jose CA with a TIS equipped airplane, I was amazed at the hornet’s nest of planes all around us and we could hardly spot any of them, even with the GNS430 telling us where they all were.  If most of the other planes didn’t have flight following or on-board traffic, it was a fairly dangerous place to be.  How often are we completely unaware of traffic?
     
     
     

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  9. Bromschwig on Feb 09, 2016

    VFR visibility and cloud clearance requirements were not put in the FARs to make sure VFR only pilots had adequate visual reference to fly visually, they were put in to be sure VFR pilots would have time to see and avoid an IFR aircraft climbing out of the top of, descending out of the bottom of, or flying out of the side of a cloud. The reason it is 500 ft below, 1000 above, and 2000 horizontally (usually) is that traffic usually descends more slowly than it climbs, and the TAS is much higher that the descent rate when flying out of the side of a cloud. Also why in higher altitudes, the numbers are even higher. Jets are required to maintain 250 kts below 10,000 ft, so above this, the distance to stay away from clouds is even greater to have the same SEE and AVOID buffer time.

    Class B airspace is the only airspace where ATC is REQUIRED to provide traffic separation between IFR and VFR traffic, therefore, no buffer time is needed for VFR pilots to see and avoid.

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