Deciphering Category Codes

Sorry if this is in the wrong forum - I didn't see a perfect forum match for this question. But I'm curious to better understand the "category" field reported by the feeder. Looking at the past few weeks of data I've collected, I see the following plane categories:

None: 31.586%
'A0': 0.965%
'A1': 11.489%
'A2': 6.531%
'A3': 26.2%
'A4': 1.06%
'A5': 21.043%
'A6': 0.033%
'A7': 1.04%
'B4': 0.048
'C2': 0.001%
'C3': 0.0006%
'D4': 0.001%
'D7': 0.004%

Other than a general wikipedia entry that these are plane classifications, I can't find any specifics of what these different categories map to - i.e.: what's A, B, C, & D? Whats C2 vs. C3? etc.

Thanks!

 

Thanks for compiling that list! I went back to see if there was any insight I could glean for the D4 I saw, or the other non-A codes, but I couldn't make anything of it. In case it's of help to you in expanding your list, here are the six distinct lines I got:

{'hex': '68baa0', 'type': 'adsb_icao_nt', 'flight': '<7#6FEBX', 'category': 'C2', 'mlat': [], 'tisb': [], 'messages': 2, 'seen': 65.7, 'rssi': -36.1}
{'hex': '97dec7', 'flight': '5H[I3U2$', 'category': 'C3', 'mlat': [], 'tisb': ['callsign', 'category'], 'messages': 2, 'seen': 15.5, 'rssi': -35.2}
{'hex': '0be3a6', 'type': 'tisb_icao', 'flight': 'R7F0NSL7', 'category': 'D4', 'mlat': [], 'tisb': ['callsign', 'category'], 'messages': 2, 'seen': 67.9, 'rssi': -34.7}
{'hex': '94ad8e', 'category': 'D7', 'version': 0, 'alert': 1, 'spi': 0, 'mlat': [], 'tisb': [], 'messages': 2, 'seen': 89.5, 'rssi': -34.2}
{'hex': 'a0c0e6', 'flight': 'N148FA ', 'alt_baro': 9300, 'alt_geom': 9475, 'gs': 104.5, 'track': 158.1, 'baro_rate': 0, 'squawk': '3261', 'emergency': 'none', 'category': 'B4', 'lat': 37.644421, 'lon': -121.79509, 'nic': 10, 'rc': 25, 'seen_pos': 69.4, 'version': 2, 'nic_baro': 1, 'nac_p': 10, 'nac_v': 2, 'sil': 3, 'sil_type': 'perhour', 'gva': 2, 'sda': 2, 'alert': 0, 'spi': 0, 'mlat': [], 'tisb': [], 'messages': 2551, 'seen': 89.3, 'rssi': -22.2}