Final answer:
FAA advisory circulars are available to pilots and can be obtained by ordering them from the Government Printing Office or accessing them online; the Federal Register is not the subscription service for these materials.
Step-by-step explanation:
FAA advisory circulars, which serve as guidance materials for the aviation community, are available to all pilots. Those interested in obtaining them can order them from the Government Printing Office or access them online. While the Federal Register does contain various notices and rules, pilots do not subscribe to this for advisory circulars. Instead, they utilize specific channels provided by the FAA.
It is also important to note that while the Federal Register and the Freedom of Information Act portal offer extensive government-related information, for aviation-specific materials such as the advisory circulars, you would directly interact with FAA resources. These materials ensure compliance with regulations which are included in the Code of Federal Regulations and are maintained by the Government Printing Office, and now also available online in a searchable format for easier access.