Class C airspace transition

[M20C pilot]

Question from newly minted private pilot working to improve my ATC communication: Yesterday I departed a non-towered field immediately adjacent to a class C. I called clearance delivery for the class C airport prior to departure to get a squawk code and request transition through their airspace to my destination. I was provided the code and departure frequency and was told "remain clear of the class C." My questions are as follows:

1. In this situation, what is the best way to contact the departure controller after taking off and changing frequency from CTAF? Do they already know who I am, and if so, would a simple "(tail number) with you (altitude)" suffice?

2. Upon departure acknowledging my tail number, am I cleared to transition through the class C despite the earlier instruction to stay clear from clearance delivery? I went around the C yesterday because I was unsure.

3. As a related question for VFR flight following, if I'm handed to an approach controller for a class C field along my route, and the controller acknowledges my tail number, am I cleared to transition through the class C airspace without further instruction?

In summary, I guess my overall question boils down to: Are the communication requirements to enter class C the same under all circumstances to transition through as for landing ?

 

[oldShar]

1) If they instructed you (how to) contact departure, then departure knows you.
If not, don't count on it. Call departure as if they were your initial call after clearing the class-E terminal space. And if that, provide full ID, location, altitude/intended altitude, and intentions or desires --- and wait for their response.

2) Expect a reprimand if they tell you to remain clear and then you bust their space. Get your verified contact with Approach/Departure before entering Charlie

3) If you are already in contact, they will tell/instruct you around the space if they don't want you there -- otherwise they will guide you thru

 

[M20C pilot]

I guess my real confusion comes up when they neither tell me to stay clear of the C nor guide me on transitioning through- i.e. neither assign heading or altitude. This seems to happen even if I explicitly request transition. For instance:

me: Approach, (my tail#), request
ATC: (my tail#), approach
me: (my tail#), (my position and altitude), enroute to (my destination), request transition through the class Charlie
ATC: (my tail#), squawk 0120 ident
ATC: (my tail#), radar contact (position), Altimeter 30.17 [and no further instruction given]

Does this mean I'm cleared through the Charlie with altitude and heading at my discretion? It's happened for two class Cs in the last month, and I feel stupid asking about the transition again, as I'm assuming that I'm cleared to enter based on the response with my tail number. Should I just ask again?

 

[M20C pilot]

"2) Expect a reprimand if they tell you to remain clear and then you bust their space. Get your verified contact with Approach/Departure before entering Charlie"

But once I have contact with departure, does that contact alone supercede the prior "remain clear of the Charlie" instruction from clearance and allow me to enter?

 

[MAKG1]

I operate within spitting distance of a busy Class C, enough to constrain the pattern. The usual instruction is "remain clear of Class C until in contact with San Jose Tower."

Once you're in contact with class C control, an instruction like that means you're good to go once in contact. If you're just told to remain clear, that's what you have to do until told otherwise. You can ask. In general, a new instruction supercedes the old, so a "climb and maintain at or below 2000" would suffice. But that's a lot of opportunity for confusion, so I'd suggest asking for clarification if that happens.

Restrictions DO survive handoffs. If one controller tells me to remain at or below 6000 due to inbound IFR traffic at 7000 and then hands me off, the traffic is most likely still there. Restrictions are terminated with "resume own navigation." It's good practice to mention restrictions at handoff.

Class C is not Class B. If you're in contact (and you've heard your tail number), in the absence of any instruction, you're good to go.

 

[frfly172]

Common for ATC to tell you to remain clear of the class C. If your that close they know where your at,they want a few minutes to get you in the trafic flow.

 

[Palmpilot]

I guess my real confusion comes up when they neither tell me to stay clear of the C nor guide me on transitioning through- i.e. neither assign heading or altitude. This seems to happen even if I explicitly request transition. For instance:

me: Approach, (my tail#), request
ATC: (my tail#), approach
me: (my tail#), (my position and altitude), enroute to (my destination), request transition through the class Charlie
ATC: (my tail#), squawk 0120 ident
ATC: (my tail#), radar contact (position), Altimeter 30.17 [and no further instruction given]

Does this mean I'm cleared through the Charlie with altitude and heading at my discretion? It's happened for two class Cs in the last month, and I feel stupid asking about the transition again, as I'm assuming that I'm cleared to enter based on the response with my tail number. Should I just ask again?

For class C, it's not called a clearance. The rule is that you are allowed to enter class C airspace if you have established two-way radio communication with the appropriate ATC facility, unless they have given you an instruction to the contrary. Your route of flight and altitude are your choice unless they tell you what altitude or route to fly. Here are the relevant portions of the regulations:

14 CFR 91.130(c) Communications. Each person operating an aircraft in Class C airspace must meet the following two-way radio communications requirements:

(1) Arrival or through flight. Each person must establish two-way radio communications with the ATC facility (including foreign ATC in the case of foreign airspace designated in the United States) providing air traffic services prior to entering that airspace and thereafter maintain those communications while within that airspace...​

and

14 CFR 91.123(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.​

Note that according to the AIM, two-way communications are not considered to be established if the controller does not say your call sign. See AIM 3-2-4c3 for details and examples.

 

[Seanaldinho]

You're being told to remain clear of the Charlie because Clearance Delivery has no control of that airspace and probably has no idea what the scope looks like at the time. Get airborne, call approach, ask to clarify if you need it.

 

[midlifeflyer]

I guess my real confusion comes up when they neither tell me to stay clear of the C nor guide me on transitioning through- i.e. neither assign heading or altitude. This seems to happen even if I explicitly request transition. For instance:

me: Approach, (my tail#), request
ATC: (my tail#), approach
me: (my tail#), (my position and altitude), enroute to (my destination), request transition through the class Charlie
ATC: (my tail#), squawk 0120 ident
ATC: (my tail#), radar contact (position), Altimeter 30.17 [and no further instruction given]

Does this mean I'm cleared through the Charlie with altitude and heading at my discretion? It's happened for two class Cs in the last month, and I feel stupid asking about the transition again, as I'm assuming that I'm cleared to enter based on the response with my tail number. Should I just ask again?

Two basic things.

One thing stands out in your sample communication and it confuses me. In your first post, you said CD assigned you a squawk code. In this one, Approach is assigning the squawk. Which is it?

If the original post is no longer "operative" and we are dealing with only the one in this post, it's easy. Far simpler than you think.

Class C does not require a "clearance" and it does not require specific transition approval. All it requires, as someone already pointed out, is the establishment of 2-way radio communication.

So in this sample, you have 2-way communication (they have used your tail number). They also gave you a discrete squawk so they have you on radar. That you are heading to your [destination] is all the additional information they need. In fact, specifically requesting a transition is technically unnecessary. Unless they give you some sort of restriction, you are free to transit the airspace as you wish (it probably means they are not busy with traffic that affects your route), although it's generally a good idea to let them know if you are going to change heading or altitude from your current altitude and a direct course though the Class C.

 

[M20C pilot]

You're being told to remain clear of the Charlie because Clearance Delivery has no control of that airspace and probably has no idea what the scope looks like at the time. Get airborne, call approach, ask to clarify if you need it.

This makes sense to me. I guess it just seemed redundant to hear "stay clear of the Charlie" from clearance delivery- Of course I'm going to stay clear of it until I contact departure, and they acknowledge my call sign, because that's the rule. But I have minimal experience talking to clearance delivery - I really just did it for practice, so I could learn to handle stuff like this appropriately. I then second guessed myself, thinking the stay clear instruction still applied after I established contact with departure, unless they specifically said I could enter. The departure controller probably wondered why I was talking to them still going well out of my way to avoid their airspace.

 

[midlifeflyer]

You're being told to remain clear of the Charlie because Clearance Delivery has no control of that airspace and probably has no idea what the scope looks like at the time. Get airborne, call approach, ask to clarify if you need it.

More likely they are telling you to remain clear of the Class C because you are departing a satellite airport and they want you to remain clear until ATC in-flight contact is made.

This is the same Clearance Delivery folks with the same control of the airspace that might say "after departure turn right heading 230; remain at or below 3,000" if you were departing the Class D primary. They don't want to say there here because, unlike the Class C primary, where Tower can amend that instruction at the time of takeoff if necessary, there's no way to do that departing the non-towered satellite and they have no idea exactly when you are taking off.

 

[M20C pilot]

Two basic things.

One thing stands out in your sample communication and it confuses me. In your first post, you said CD assigned you a squawk code. In this one, Approach is assigning the squawk. Which is it?

If the original post is no longer "operative" and we are dealing with only the one in this post, it's easy. Far simpler than you think.

Class C does not require a "clearance" and it does not require specific transition approval. All it requires, as someone already pointed out, is the establishment of 2-way radio communication.

So in this sample, you have 2-way communication (they have used your tail number). They also gave you a discrete squawk so they have you on radar. That you are heading to your [destination] is all the additional information they need. In fact, specifically requesting a transition is technically unnecessary. Unless they give you some sort of restriction, you are free to transit the airspace as you wish (it probably means they are not busy with traffic that affects your route), although it's generally a good idea to let them know if you are going to change heading or altitude from your current altitude and a direct course though the Class C.

Thanks for reply and sorry for confusion- they are 2 separate scenarios to illustrate this general area of communication where I've been second guessing myself due to minimal real world experience. Your answer to the second scenario make makes perfect sense as it is what I've read and been taught. Any comment on the first?

 

[midlifeflyer]

I think CD gave you the "remain clear" instruction because they couldn't issue departure instructions into the Class C for the reasons I mentioned earlier; they want you to wait to make contact in the air.

I suspect the "remain clear" was no longer in effect based on the later contact with TRACON, but it's generally a bad idea to either assume or infer an approval when you have previously heard a "remain clear."

So I would clarify. The clarification could be something as simple as "confirm transit though the Class C at [your selected altitude] is approved."

 

[M20C pilot]

I think CD gave you the "remain clear" instruction because they couldn't issue departure instructions into the Class C for the reasons I mentioned earlier; they want you to wait to make contact in the air.

I suspect the "remain clear" was no longer in effect based on the later contact with TRACON, but it's generally a bad idea to either assume or infer an approval when you have previously heard a "remain clear."

So I would clarify. The clarification could be something as simple as "confirm transit though the Class C at [your selected altitude] is approved."

Perfect- thank you. And cool website BTW. I started training 2 years ago at roughly the same age that you did.

 

[PeeGee]

I think CD gave you the "remain clear" instruction because they couldn't issue departure instructions into the Class C for the reasons I mentioned earlier; they want you to wait to make contact in the air.

I suspect the "remain clear" was no longer in effect based on the later contact with TRACON, but it's generally a bad idea to either assume or infer an approval when you have previously heard a "remain clear."

So I would clarify. The clarification could be something as simple as "confirm transit though the Class C at [your selected altitude] is approved."

Agreed.

Clearance delivery is a tower position, in the cab, not in the radar room or approach facility depending how it's set up. Remain clear is a cya, it's not "his" airspace and probably doesn't want you to think you've established 2 way radio communications based on what has transpired.

My assumption (and I'm making a lot of them here) is the data he received from you would pass to the approach controller so he knows who you are since he tagged you up with a code, and while the restriction stays in effect until canceled, he probably in reality would not advise the next controller of the restriction unless there's a way for their automation to pass it.

When in doubt speak up and ask if you're unsure.

 

[Kritchlow]

If the last clearance was "remain clear of C airspace", I would remain clear until I hear otherwise.

 

[Shawn]

If the last clearance was "remain clear of C airspace", I would remain clear until I hear otherwise.

Agreed...in that scenario as soon as I made contact with approach control in the air after departure the initial call would be as simple as:

"Approach, Cessna 12XYZ, 1200' climbing 3000', request class C transition to [destination]"

 

[poadeleted20]

I guess my real confusion comes up when they neither tell me to stay clear of the C nor guide me on transitioning through- i.e. neither assign heading or altitude. This seems to happen even if I explicitly request transition. For instance:

me: Approach, (my tail#), request
ATC: (my tail#), approach
me: (my tail#), (my position and altitude), enroute to (my destination), request transition through the class Charlie
ATC: (my tail#), squawk 0120 ident
ATC: (my tail#), radar contact (position), Altimeter 30.17 [and no further instruction given]

Does this mean I'm cleared through the Charlie with altitude and heading at my discretion? It's happened for two class Cs in the last month, and I feel stupid asking about the transition again, as I'm assuming that I'm cleared to enter based on the response with my tail number. Should I just ask again?

This question is answered in 14 CFR 91.130 and AIM Section 3-2-4, both of which should be in your FAR/AIM book.

 

[Fearless Tower]

Here's a related question. Let's say that you are flying under the Class C shelf (you're at 1000 ft and the floor is 1200') and you want to transition the Class C surface area. Do you need to call Approach, or do you just call the Class C tower?

 

[PeeGee]

Approach

 

[Kritchlow]

Here's a related question. Let's say that you are flying under the Class C shelf (you're at 1000 ft and the floor is 1200') and you want to transition the Class C surface area. Do you need to call Approach, or do you just call the Class C tower?

This isn't an answer to that question specifically, but....
Years ago I used to fly checks in a C310 at night. One of my legs was ALB to EWR. I would fly the Hudson the whole way, below the (then TCA) and talk to nobody after Albany. My first call would be Newark tower inbound at "The Lady" (Staute of Liberty). Always got a right turn in for 29. Did it more times than I can count. Never an issue.

 

[MAKG1]

Approach

Maybe.

But all of the C's -- and even the few B's -- I've transited below the shelf and into the surface area want me talking to Tower unless I've just gone missed on an instrument approach.

There isn't any global rule, and if you get it wrong, you'll be handed off immediately. No big deal.

 

[PeeGee]

There are always exceptions, however per the aim, services provided within class c aispace:

Aircraft Separation. Separation is provided within the Class C airspace and the outer area after two-way radio communications and radar contact are established. VFR aircraft are separated from IFR aircraft within the Class C airspace by any of the following: 1. Visual separation. 2. 500 feet vertical; except when operating beneath a heavy jet. 3. Target resolution


As a general rule if the controller has Windows they only care about concrete. If they have radar they care about airspace. The tower may have a d bright, but why would you contact a facility that is incapable of providing the service you require? Ie radar separation.

 

[MAKG1]

Except some towers, particularly in B and C airspace, have both windows and radar.

Both of the D towers I use regularly have radar feeds, one from the neighboring C and the other from a neighboring Federal D.

I've yet to experience any tower that didn't want to talk to me when transitioning their airspace anywhere near pattern altitude, even if I have no stated intention to land there.

If you're in the surface area below the shelf, any 121 traffic at those altitudes is past the FAF and talking to tower.

Besides, if you disagree with SOP at NorCal, you should argue with them. I just transition their airspace.

 

[PeeGee]

Except some towers, particularly in B and C airspace, have both windows and radar.

Both of the D towers I use regularly have radar feeds, one from the neighboring C and the other from a neighboring Federal D.

I've yet to experience any tower that didn't want to talk to me when transitioning their airspace anywhere near pattern altitude, even if I have no stated intention to land there.

If you're in the surface area below the shelf, any 121 traffic at those altitudes is past the FAF and talking to tower.

Besides, if you disagree with SOP at NorCal, you should argue with them. I just transition their airspace.

That's called a d bright.
Class d has nothing to do with class c.

I have friends at norcal, if I cared about their local procedures I'd go to the source and not the internet.

where did ANYONE suggest entering anyone's airspace without communicating with them?

2 more things, first if they're inside the faf they were put there by approach. Second, he did say the surface area but he could be entering from below and it's easier for approach to tag him up if he isn't already.

WHY do you INSIST on making a simple, every day occurrence complicated? CALL APPROACH. It's their job.

 

[Velocity173]

Here's a related question. Let's say that you are flying under the Class C shelf (you're at 1000 ft and the floor is 1200') and you want to transition the Class C surface area. Do you need to call Approach, or do you just call the Class C tower?

I've done it both ways and they don't mind. While the sectional says to contact approach 20 miles out, that's really to just assist with sequencing.

Plenty of class Cs utilize certified displays and based on the local controller's qualifications (BRITE course / approach certified) they can use it for basic radar functions. Also, plenty of Cs have the approach controller sitting right next to local. Where my brother works, they rarely work out of the radar room. It's a quick coordination for the local controller to tell approach "hey, see that xxxx code 7 miles west at 1,000?"

 

[PeeGee]

they rarely work out of the radar room.

Uh, maybe in like a level 6 up down. A lot of B's and C's aren't up downs and the tracon is completely separate. But lets make assumptions and plan our actions based on what the configuration might be instead of what it should be!

Also, while there are a few limited approach control towers, most brights are not there for radar separation, it is there for sequencing.

Again, why would you contact a facility that is not equipped to provide the service you require while transiting a busy terminal environment?

AIM 4-2-4e
e. A few of the radar equipped towers are
authorized to use the radar to ensure separation
between aircraft in specific situations, while still
others may function as limited radar approach
controls. The various radar uses are strictly a function
of FAA operational need. The facilities may be
indistinguishable to pilots since they are all referred
to as tower and no publication lists the degree of radar
use. Therefore, when in communication with a
tower controller who may have radar available, do
not assume that constant radar monitoring and
complete ATC radar services are being provided.

 

[Velocity173]

Uh, maybe in like a level 6 up down. A lot of B's and C's aren't up downs and the tracon is completely separate. But lets make assumptions and plan our actions based on what the configuration might be instead of what it should be!

Also, while there are a few limited approach control towers, most brights are not there for radar separation, it is there for sequencing.

Again, why would you contact a facility that is not equipped to provide the service you require while transiting a busy terminal environment?

AIM 4-2-4e
e. A few of the radar equipped towers are
authorized to use the radar to ensure separation
between aircraft in specific situations, while still
others may function as limited radar approach
controls. The various radar uses are strictly a function
of FAA operational need. The facilities may be
indistinguishable to pilots since they are all referred
to as tower and no publication lists the degree of radar
use. Therefore, when in communication with a
tower controller who may have radar available, do
not assume that constant radar monitoring and
complete ATC radar services are being provided.

It's all facility / controller dependent. Your statements are no more than absolutes any more than mine are. As MAKG said, where he flys they want him contacting tower for the transition. I transition a surface C on a regular basis and while I contact approach, half the time they'll put me on tower for the transition.

Tower CAN use the BRITE or whatever other CTRD for basic radar functions depending on the local procedures in effect and if the particular local controller is either approach rated or passed a BRITE qualification.

As far as being coombined in the tower with approach? I know several that work approach out of the tower after a certain time of night. It's not that rare.

 

[PeeGee]

It's all facility / controller dependent. Your statements are no more than absolutes any more than mine are. As MAKG said, where he flys they want him contacting tower for the transition. I transition a surface C on a regular basis and while I contact approach, half the time they'll put me on tower for the transition.

Tower CAN use the BRITE or whatever other CTRD for basic radar functions depending on the local procedures in effect and if the particular local controller is either approach rated or passed a BRITE qualification.

As far as being coombined in the tower with approach? I know several that work approach out of the tower after a certain time of night. It's not that rare.

Mid shift is a completely different configuration than days, is the guy flying at 0100 local now? It's not at all pertinent to the discussion at hand.

Those basic local functions are very clearly laid out in the 7110.65. You won't find radar sep in them except in very limited circumstances.

But what do I know

 

[Velocity173]

Mid shift is a completely different configuration than days, is the guy flying at 0100 local now? It's not at all pertinent to the discussion at hand.

Those basic local functions are very clearly laid out in the 7110.65. You won't find radar sep in them except in very limited circumstances.

But what do I know

Don't have a clue what your background is (PG operating initials?).You've been on this forum for less than a month.

Yes, those are the basic local functions for someone who doesn't rotate between the tower and approach. Otherwise, IAW the provisions of 7210.3, local can use the CTD for any terminal approach control function. Even with that, depending on facility letters, what each local controller can do will vary.

In my experience, when it's busy in the surface of the C, approach wants me talking to tower for the transition. Either way, you can call tower or approach, each will either keep you or put you on the freq of the position they want you talking to. Takes only a few seconds.

 

[deyoung]

So I would clarify. The clarification could be something as simple as "confirm transit though the Class C at [your selected altitude] is approved."

Perhaps it's a bad habit (which is why I mention it here, to ask), but I tend to use more conversational phraseology in this situations, unless everyone is obviously unusually busy. So, something like "Clearance instructed me to remain clear of Charlie; confirm that is still in effect?"

Poor form, or doesn't matter?

 

[midlifeflyer]

Perhaps it's a bad habit (which is why I mention it here, to ask), but I tend to use more conversational phraseology in this situations, unless everyone is obviously unusually busy. So, something like "Clearance instructed me to remain clear of Charlie; confirm that is still in effect?"

Poor form, or doesn't matter?

Doesn't matter. Usually. Your form seems just fine to me.

Having flown out of a very busy Class D underlying Class B, where the crispness of communication can mean the difference some days between "make right base" or "squawk 5929"on the one hand and "remain clear and call us back later," on the other, I've become a fan of "shorter and cleaner is better". I don't make a distinction between busy and non-busy airspace as a matter of SOP - the manner of speaking becomes automatic; you think short instead if thinking how to make it short. There are exceptions of course.

.

 

[fiveoboy01]

Perhaps it's a bad habit (which is why I mention it here, to ask), but I tend to use more conversational phraseology in this situations, unless everyone is obviously unusually busy. So, something like "Clearance instructed me to remain clear of Charlie; confirm that is still in effect?"

Poor form, or doesn't matter?

It wouldn't think it would be poor form at all however it's not necessary...

As mentioned, it doesn't matter what CD told you prior, if you've established 2-way communication with approach and they do not specifically tell you to remain clear, you're ok to enter.

 

[midlifeflyer]

It wouldn't think it would be poor form at all however it's not necessary...

As mentioned, it doesn't matter what CD told you prior, if you've established 2-way communication with approach and they do not specifically tell you to remain clear, you're ok to enter.

Are you absolutely, positively, 100% certain that an instruction from ATC (in this case CD) to "remain clear" after being in voice contact, your N-number used, and a squawk code issued is automatically negated by a later contact with someone else from ATC? I am not.

So, if you were given a "remain at or below" instruction by CD or Tower as part of your departure instructions or takeoff clearance from a Class C primary, it would automatically no longer be in effect when you were switched to Approach unless they repeated it? If not, what do you see as being the difference?

 

[fiveoboy01]

Are you absolutely, positively, 100% certain that an instruction from ATC (in this case CD) to "remain clear" after being in voice contact, your N-number used, and a squawk code issued is automatically negated by a later contact with someone else from ATC? I am not.

Absent an instruction to remain clear, yes. It's in the FARs..

So, if you were given a "remain at or below" instruction by the Tower as part of your takeoff clearance from a Class C primary, it would automatically no longer be in effect when you were switched to approach? unless they repeated it? If not, what do you see as being the difference? The different chairs in the Tower they are sitting on?

I see that as a different situation as you're already in the surface area as opposed to entering the C from the outside.

I am always given "at or below 3000" by clearance delivery, when I switch from tower to departure I always get an altitude instruction. Either "remain below xxxx" or "altitude your discretion".

 

[MAKG1]

Absent an instruction to remain clear, yes. It's in the FARs...

Where in the FARs does it say instructions expire on handoffs?

He has an instruction to remain clear.

Instructions do expire with other instructions, but not on handoffs. If you get "radar contact 2 miles north of Podunk Airport," you're still on the hook for the previous instruction.

I once got instructed to remain clear of Oakland Class C, and steered away from it, by a neighboring tower. Turns out there was a real good reason. A 777 had just crashed at SFO less than 30 minutes prior and closed it, and NorCal was swamped with airliner diversions, at least some of which were going to Oakland.

 

[fiveoboy01]

I stand corrected on that. I was thinking that CD isn't technically ATC and it's not a handoff... You and Mark are right, I've never had that situation where I'm calling CD at a different facility than where I'm presently waiting to take off so I've shown my ignorance here

ETA - my "home" airport is just northwest of MSN, in a small cutout in the surface area(see my avatar). I don't call clearance at MSN, I just take off, head west and remain below 2300, and call MSN approach for a squawk. Are there certain airports such as the OP's example that you're required to call the CD of an adjacent class C or D airport to get a squawk code prior to departing from a non-towered field???

 

[bullwinkle]

Most Class C spaces are not that tall. If told to stay clear and weather permits, you can climb over the top and continue on your merry way over the space.

Flying over the Jacksonville Class C on Flight Following last year I ran into a cloud deck and told the controller I needed to descend into the Class C to maintain VFR. He told me to go ahead, but stay at or above 3500ft. I stayed at 3800ft and watched the airliners pass under me. I hope my wake turbulence didn't get 'em.

 

[midlifeflyer]

ETA - my "home" airport is just northwest of MSN, in a small cutout in the surface area(see my avatar). I don't call clearance at MSN, I just take off, head west and remain below 2300, and call MSN approach for a squawk. Are there certain airports such as the OP's example that you're required to call the CD of an adjacent class C or D airport to get a squawk code prior to departing from a non-towered field???

No. It's just convention. Maybe more local than anything. If you are close, expect it to be necessary or desirable to enter the Class C for your route of flight and close enough for the frequency to be available, why not try to get your approval or squawk in advance so they are expecting you? Before KFTG, just a mile east of the KDEN surface area, grew a tower, it was not unusual for pilots wanting to head west to call Denver Tower from the ground to ask for a Bravo clearance and transition.


Think of it as asking from Flight Following from a Class D Tower. Not a requirement, nice to have in advance so they are expecting you, and some Towers will make those arrangements while others won't.

 

[Sac Arrow]

I've never been handed off to a class C tower for a transit. Class D can be a different situation though, unlike class C, sometimes approach does not control the airspace within D, in which case you would be handed off to the tower if they know you are going to transit it.