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Thread: Squawk Codes

  1. #1
    StuSEL's Avatar
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    Squawk Codes

    I was just wondering what determines the squawk codes that aircraft are issued. I've noticed four blocks of codes in use at my local up/down ATCT:
    1.) VFR pattern
    2.) VFR departure
    3.) inter-facility IFR
    4.) IFR with a destination outside of the local airspace.

    Are there any other situations? Also, is the traffic counter paired with the computer that issues squawk codes? I've noticed that I am issued a different code if I go from VFR flight following to IFR, or enter the traffic pattern for touch and gos after being VFR flight following earlier. Just wondering why that is.

  2. #2
    Roddy_Piper's Avatar
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    Re: Squawk Codes

    usually a facility is allocated a local subset of codes. for instance XYZ tracon will be assigned 0421-0457 as a subset. if you want to tag someone up within your airspace then one of those codes will be assigned. however, if you want to put the flight plan into the NAS then you will be assigned a different code by the host in order to process through the NAS.

    it depends on how you ask for a code. a local VFR pop-up that will not be processed will usually be issued a code within your local sub-set. however, if you request (type in) a full flight plan then you will be assigned the NAS code.

    every facility will be different. for my facility it's the 42xx subset for any aircraft that will stay within my airspace. the neighboring RAPCON has their own 04xx subset. we can interact between each other on the local subset, but need to get a NAS code if were gonna process through the center.

  3. #3
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    Re: Squawk Codes

    The assignment of a new code when you go VFR to IFR is also required to enable Minimum Safe Altitude Warning reporting (the alarm that makes us tell you "low altitude alert.") Squawk codes from the facility's VFR Code Bank are MSAW inhibited, so it requires a change when you go IFR.

    Interestingly, our radar system allows us to disable MSAW on an IFR flight (like when they cancel IFR) but we can't enable it on a VFR flight. So IFR -> VFR, doesn't require a new code here, but VFR -> IFR does.

    Also all the reasons Roddy mentioned above. If you fly near a common boundary for two centers, you might get a new code when crossing the boundary because that center is on a different host computer and needs you on a code assigned from its own system.

  4. #4
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    Re: Squawk Codes

    More than you probably ever wanted to know about transponder code allocation:

    http://flsc.org/Instruction/JO%207110.66D%20.pdf

  5. #5
    StuSEL's Avatar
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    Re: Squawk Codes

    Thanks guys! Much appreciated.

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