**Direct answers to your questions** - *What are ADS-B ICAO addresses* 🠪 permanent ICAO addresses. - *What are ADS-B self-assigned addresses* 🠪 Anonymous addresses. - *What are TIS-B addresses* 🠪 permanent ICAO addresses. - *What are TIS-B trackfile ID* 🠪 The 12 random bits assigned to tracks by a ground station for Mode A/C targets and used to create the temporary TIS-B pseudo-addresses. - *Collision between the two GLD 90 ICAO addresses*. 🠪 Permanent addresses are unique for aircraft but can collide because of errors when configuring the equipment. In addition ground vehicles are allowed to share the same permanent address when they are distant by more than 1,000km. See section *Duplicates*. - *Collision between addresses of all kinds* 🠪 See section *Duplicates*, as it cannot be summarized here. - *Examples of the four types* 🠪 permanent ICAO addresses are part of blocks allocated to a State registry, and not all blocks are currently allocated. Uruguay is allocated the block of addresses starting with 0xE90 (1110 10 010 000), so 0xE90AAA (1110 10 010 000 1010 1010 1010) is a permanent address for an aircraft registered in Uruguay. For the other types, any valid 24-bit combination can be found as they are random. Nothing distinguishes them. I'm adding detailed explanations below. Most of the information comes from ICAO [Annex 10 volume III - Communication Systems][1]. ---- **ICAO 24-bit address overall** - Aircraft, aerodrome vehicles, surface obstacles and Mode S surface equipments used for surveillance and radar monitoring can be assigned an address. - An aircraft is assigned a unique address. Surface vehicles and devices can share the same address, provided they are distant by more than 1,000km. - The address is assigned e.g. to the aircraft. It is not assigned to a particular equipment, all equipments aboard the aircraft use the same ICAO address (1090 ES and 978 UAT). - Valid addresses are all combinations of 24 bits, excluding all 0s and all 1s. **TIS-B pseudo-address** Addresses mentioned above are used by aircraft working with Mode S. In particular ADS-B periodic messages allow aircraft to track other aircraft positions in real time. This excludes aircraft in Mode A/C from the tracking. TIS-B is used to fill the gap. The ground station tracking the Mode A/C aircraft sends TIS-B position reports to Mode S aircraft, related to the Mode A/C aircraft. But in Mode S all aircraft are identified by their ICAO address, not by their Mode A/C squawk code. The ground station must temporarily identify the Mode A/C aircraft with a pseudo-address made of the 12 bits of the squawk code and 12 random bits assigned to the track. See [this question][3] for details (with a bit of luck, @DeltaLima will post an answer here, he's a specialist in this field) **Permanent address** A permanent address is assigned by the State registry. This is a two-step process: - Address blocks are allocated by ICAO to State registries, per table 9.1 in [Annex 10][1]. - The State registry then assigns addresses to aircraft by picking in its allocated block. Special blocks are allocated to ICAO and not available to State registries. - 1000-10-011-001-00 (1000-address block) - 1111-00-001-001-00 (1000-address block) - 1111-00-000 (32,000-address block) **Temporary address** ICAO block 1111-00-001-001-00 is used for temporary addresses, when users are waiting for the registering procedure to complete. Assignment is administered by ICAO, not by a State registry. **Anonymous address (for UAT only)** For privacy purposes, a pseudo-random self-assigned address can be built by the aircraft equipment, starting from the permanent address if there is one, else from the current time, [see this question for details][2]. **Duplicates** The probability to see the same address in a given area is very low, but not null, because: - The same permanent address can be re-used by surface equipments distant by more than 1,000km. - Errors can be made while configuring the permanent address in the equipment (some questions on the site relate to flight trackers identifying the wrong aircraft due to address configuration mistakes). - Self-assigned UAT addresses conflicting either with a permanent address or another self-assigned address. The probability is lower than the one of a permanent address duplicate. - Perhaps the same for self-assigned TIS-B target addresses. **GDL 90** All address types can be found in field 'aa aa aa' of a [GDL 90][4] message. The uniqueness of this field, even combined with field 't' cannot be guaranteed. How addresses call collide has been explained in section *Duplicates* [1]: https://www.bazl.admin.ch/bazl/en/home/themen/legislation/anhaenge-icao.html [2]: https://aviation.stackexchange.com/q/74751/3201 [3]: https://aviation.stackexchange.com/q/17610/3201 [4]: https://www.faa.gov/sites/faa.gov/files/air_traffic/technology/adsb/archival/GDL90_Public_ICD_RevA.PDF