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When am I allowed to change my transponder code to 1200? Is it after clearing the boundary of controlled "radio-contact-required with transponder" airspace?

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  • $\begingroup$ Why are you so desperate to change to 1200? When squawking a discreet code (e.g. one given by ATC), they will keep an eye on you on the radar - making sure you do not collide with other traffic or enter restricted airspaces. When squawking 1200, they lose this ability, and you essentially lose a very strong safety net that could prevent dangerous situations. $\endgroup$ – J. Hougaard Jun 8 '16 at 7:45
  • $\begingroup$ @J.Hougaard changing to 1200 and dropping radar service doesn't make you invisible to ATC. One great reason to drop ATC is for area maneuvers. It can be annoying to have to get permission every time you want to turn. So, for lessons; that's one reason. $\endgroup$ – Ryan Mortensen Jun 8 '16 at 7:56
  • $\begingroup$ @RyanMortensen Sure, you are not invisible. But you are anonymous. Even if ATC can see two 1200 tracks on a collision course, there is not much they can do about it, since they do not know who it is. As for "getting permission every time you want to turn", I don't see any correlation between squawking a discreet code and being under ATC control. If you are in uncontrolled airspace, you can "do as you want" - no matter what your transponder code is. $\endgroup$ – J. Hougaard Jun 8 '16 at 8:01
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ATC will tell you something like, "N1234R radar service terminated. Squawk VFR. Frequency change approved; good day" which you will repeat back as an instruction.

You do not change from the assigned transponder code until instructed.

If you're in a hurry to get away from ATC, you may request to terminate radar service as soon as you are out of their, "radio-contact plus transponder required," airspace.

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Normally, as a courtesy, you terminate radar service by notifying ATC in a handshake as in Mortensen's answer. In most cases this never happens, because as soon as you leave their zone ATC will terminate service unilaterally--you don't have to ask for it.

If you are flying under IFR rules in any airspace except G, you must have a clearance and be using the code currently assigned to you under the clearance.

If you are flying VFR, you normally use code 1200. You can change to 1200 whenever you want, but if you previously had a clearance, you will immediately lose your clearance when you switch to 1200.

Therefore, the general principle is that you can switch to 1200 whenever you are flying VFR and do not require a clearance to be where you are. In class B, C, and D you are required to be in "voice contact" with ATC, which could be construed to require a handoff. In class E you are only required to be in voice contact if you are in the vicinity of a towered airport, in which case you have to be in voice contact with the tower (not ATC). So, basically what this means is that if you are in G or E (not near an airport) you can go to 1200 whenever you want. In B, C, D you should always do signoffs ("Cessna 5678 Golf terminating radar service"). If you are in an area that requires a clearance, you must get permission to terminate radar service.

So, your own statement is basically correct: once you leave a radio-contact required area, you are free to go VFR. Note that if you abandon a flight plan and go VFR without notifying ATC, even if you are in a radio-free zone, they can get miffed about that because it messes up their rack, so it is always a good practice to explicitly terminate your service/flight plan before switching to VFR and going numberless.

Example: You are flying VFR through a restricted military operating area and have a clearance to do so. You must stay on code as long as you are in the restricted area, because you require a clearance to be there.

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    $\begingroup$ Terminating radio service is not a courtesy; it is a requirement if you want to switch to 1200. Also, one cannot fly IFR in class G; you probably don't mean to imply that, but that's how it sounds (or am I wrong?). $\endgroup$ – Ryan Mortensen Jun 8 '16 at 13:29
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    $\begingroup$ It may not be your intention, but your wording suggests that pilots can just switch from a squawk assigned by ATC to 1200 if they feel like it, which isn't the case (see 14 CFR 91.123(b)). And you might want to modify your last example: VFR flights don't need a clearance to enter a MOA. $\endgroup$ – Pondlife Jun 8 '16 at 14:20
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    $\begingroup$ @RyanMortensen Where is it stated that you cannot fly IFR in class G airspace? If true, it must be a rule specific to the FAA. IFR in class G happens daily at my local airport. $\endgroup$ – J. Hougaard Jun 8 '16 at 14:24
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    $\begingroup$ @TylerDurden Pondlife is right. ATC providing you with a squawk code and telling you to use it is an instruction, and it has no void time. You need to tell them you want to drop service or wait for them to tell you that they are dropping service. $\endgroup$ – Ryan Mortensen Jun 8 '16 at 15:13
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    $\begingroup$ @TylerDurden once again, it isn't about a requirement to talk to ATC where you are. It is about following the ATC instructions that you have already accepted. Also, once again, 14 CFR 91.123(b) "(b) Except in an emergency, no person may operate an aircraft contrary to an ATC instruction in an area in which air traffic control is exercised." Squawking a specific code is an instruction. ATC control is exercised in class E airspace. $\endgroup$ – Ryan Mortensen Jun 8 '16 at 17:50

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