I am trying to make sense of the SID structures from the FAA's 28 day NASR subscription files (SSD and/or STARDP, raw data in txt files), and I have two questions.
First, I notice that there are SIDs without any path: no transition FIX/NAVAIDs and no main bodies. What's the point of referencing a SID that does not contain anything else except the airport(s)? Take this SID for example (no other records exist for BELLEVUE SID):
D0075 NA N4729353W12212567RNT BELVU3.BELVU BELLEVUE THREE D0075 AA N4729353W12212567RNT
Second, another thing that prevents me from interpreting these SIDs is the difference between "NA" airports and "AA" airports. From the layout file which explains how to read and interpret the records, I read that "If there are airports served by the DP that are not served by any body, there will be one or more records describing these airports, with the FIX/facility type code field containing an 'NA'".
The problem is that in each SID where an 'NA' record exists, another one 'AA' record exists for the SAME airport described by the 'NA' record, so I cannot really understand if they are served by the SID's main body (if any). I am not sure how to interpret this, or the fact that SIDs like the one already mentioned (BELLEVUE) contain neither a main body nor any transition paths.
Another example is this SID; every "NA" airport seems to be also an "AA" airport:
D0161 NA N3832426W08950067BLV CARDS1.CSX CARDS ONE D0161 NA N3844553W09022121STL D0161 NA N3834133W09009183CPS D0161 NA N3853237W09002456ALN D0161 NA N3839436W09039074SUS D0161 AA N3832426W08950067BLV D0161 AA N3844553W09022121STL D0161 AA N3834133W09009183CPS D0161 AA N3853237W09002456ALN D0161 AA N3839436W09039074SUS D0161 ND N3845099W09021395CSX CARDS1.BDF BRADFORD TRANSITION D0161 R N3921383W09013256SKYPE K5 D0161 R N4004061W09003391SKUTR K5 D0161 NW N4109350W08935163BDF D0161 ND N3845099W09021395CSX CARDS1.LEBOY LEBOY TRANSITION D0161 R N3922076W09033098DEECE K5 D0161 R N3926003W09034230LEBOY K5 D0161 ND N3845099W09021395CSX CARDS1.NEENS NEENS TRANSITION D0161 R N3923033W09025555MYKEY K5 D0161 R N4014535W09031538NEENS K5 D0161 ND N3845099W09021395CSX CARDS1.SPI SPINNER TRANSITION D0161 R N3919223W09000200TEWHY K5 D0161 NW N3950230W08940398SPI
Am I missing something here? I apologize for the lengthy post but I would really appreciate if someone could point me to the right direction.