Airplane, I can't believe these people spent a week sending you confusing replies instead of just answering your question in plain English.
You are correct in that SP1 is different than SDK1, etc.
SP1 & SP2 are Service Packs (Bug Fixes) that correct problems with how the sim (FSX) runs.
SDK1, 1A, & SDK2 are different versions of the Software Development Kit that was included if you bought the Deluxe version of FSX.
The SDK installs separately from the main FSX program, in some other folders. If you bought the Deluxe version you would have been given the option to install the SDK after the installation of the main FSX program was complete. Then you would have to install the patches to the SDK to match the same level of patches (SP1, SP2, etc.) that you applied to the main FSX program. Those were the initial release (RTM-Release to Manufacturing), SP1, SP2, Deluxe (included SP1, SP2, & the SDK), Acceleration, & now Steam versions.
Now, here is what the SDK (Software Development Kit) is:
It is an incomplete, jumbled up mess of little bits of information, & small executable programs, that allow you to edit or create: scenery, land class, terrain mesh, airplanes or other vehicles, edit sounds, panels & gauges, & many other things associated with FSX.
There is no comprehensive guide that explains everything. Rather it seems like the Microsoft Developers just dumped everything they could in there, & most if it is not well documented, or explained - typical computer geeks!
FSDeveloper.com is website that explains how to use some of the Development Tools included in the SDK, & they have some of their own tools also. It is a good resource, but again much of the documentation is sparse & not comprehensive.
Nevertheless, ADE (Airport Design Editor) needs to access some of those tools included in the SDK. ADE needs to know which folder to look in to find the appropriate tool in the SDK folders you have already installed on your hard-drive somewhere. All you need to do is to establish the link (point to the right folder) probably by filling in a dialog box or something. Other than that you don't need to have the SDK in any special folder.
Finally, I'm sorry to say that the only place I know of that you can get the SDK is from the Deluxe Version of FSX. As I recall it was $10 or $15 dollars more than the basic program, only because it included the hodge-podge SDK, & SP1 & SP2.
You might be able to get the SDK off the internet somewhere, & it might be included in those links on FSDeveloper.com. I can't tell you for sure, because if I click those links to see what is in them it might try to over-write my own SDK folders, & I don't want to risk that.
I hope you can find what you need, Good Luck.
