Aeronautical Information Manual (AIM), page 300
AIM 12/10/15 TBL 5-1-5 Aircraft Surveillance Equipment, Including Designators for Transponder, ADS-B, ADS-C, and Capabilities INSERT N if no surveillance equipment for the route to be flown is carried, or the equipment is unserviceable, OR INSERT one or more of the following descriptors, to a maximum of 20 characters, to describe the serviceable surveillance equip- ment and/or capabilities on board: SSR Modes A and C A Transponder - Mode A (4 digits – 4096 codes) C Transponder - Mode A (4 digits – 4096 codes) and Mode C SSR Mode S E Transponder - Mode S, including aircraft identification, pressure-altitude and extended squitter (ADS-B) capability H Transponder - Mode S, including aircraft identification, pressure-altitude and enhanced surveillance capability I Transponder - Mode S, including aircraft identification, but no pressure-altitude capability L Transponder - Mode S, including aircraft identification, pressure-altitude, extended squitter (ADS B) and enhanced surveil- lance capability P Transponder - Mode S, including pressure-altitude, but no aircraft identification capability S Transponder - Mode S, including both pressure-altitude and aircraft identification capability X Transponder - Mode S with neither aircraft identification nor pressure-altitude capability NOTE- Enhanced surveillance capability is the ability of the aircraft to down-link aircraft derived data via a Mode S transponder. Followed by one or more of the following codes if the aircraft has ADS-B capability: B1 ADS-B with dedicated 1090 MHz ADS-B "out" capability B2 ADS-B with dedicated 1090 MHz ADS-B "out" and "in" capability U1 ADS-B "out" capability using UAT U2 ADS-B "out" and "in" capability using UAT V1 ADS-B "out" capability using VDL Mode 4 V2 ADS-B "out" and "in" capability using VDL Mode 4 NOTE- File no more than one code for each type of capability; for example, file B1 or B2,but not both. Followed by one or more of the following codes if the aircraft has ADS-C capability: D1 ADS-C with FANS 1/A capabilities G1 ADS-C with ATN capabilities EXAMPLE- 1. SDGW/SB1U1 {VOR, ILS, VHF, DME, GNSS, RVSM, Mode S transponder, ADS-B 1090 Extended Squitter out, ADS-B UAT out} 2. S/C {VOR, ILS, VHF, Mode C transponder} 5-1-22 Preflight
Page 300 of the Aeronautical Information Manual (AIM.pdf)
AIM: Official Guide to Basic Flight Information and ATC Procedures