sensors Mode-S transponder
A0566A
ICAO 24-bit transponder address · allocated to United States
Currently assigned to N12021 · BOEING 787-10 Dreamliner · operated by UNITED AIRLINES INC
- Hex
- A0566A
- Octal
- 50053152
- Decimal
- 10,507,882
- Country
- US
- Tail
- N12021
- Type
- B78X
- Flights observed
- 207
- Distinct callsigns
- 20
- Country
- US
- Last broadcast
- 5d ago
Last known position
Country allocation
The ICAO 24-bit address A0566A falls within the block assigned to United States (US) by ICAO Annex 10, Volume III. Every aircraft registered in United States receives a permanent address from this block at the time of registration; the address stays with the airframe even if the aircraft is re-registered to a different operator within the country.
Callsign history 20 distinct
| Callsign | Airline | Flights | Last seen |
|---|---|---|---|
| UAL971 | - | 15 | 2026-07-02 |
| UAL970 | - | 14 | 2026-07-01 |
| UAL423 | - | 12 | 2026-06-29 |
| UAL415 | - | 11 | 2026-06-25 |
| UAL416 | - | 10 | 2026-06-25 |
| UAL945 | - | 9 | 2026-06-22 |
| UAL944 | - | 8 | 2026-06-21 |
| UAL422 | - | 8 | 2026-06-28 |
| UAL995 | - | 7 | 2026-07-14 |
| UAL972 | - | 7 | 2026-07-13 |
| UAL882 | - | 7 | 2026-06-20 |
| UAL38 | - | 7 | 2026-07-20 |
| UAL124 | United Airlines | 7 | 2026-07-24 |
| UAL987 | - | 6 | 2026-07-04 |
| UAL986 | - | 6 | 2026-07-04 |
| UAL973 | United Airlines | 6 | 2026-07-26 |
| UAL39 | United Airlines | 6 | 2026-07-19 |
| UAL125 | United Airlines | 6 | 2026-07-25 |
| UAL994 | United Airlines | 4 | 2026-07-25 |
| UAL881 | - | 4 | 2026-06-17 |
Recent flights last 50
| Date | Flight | Route | Takeoff | Landing | Duration |
|---|---|---|---|---|---|
| 2026-07-26 | UAL973 | BRU → ORD | Jul 26, 08:40 UTC | Jul 26, 16:50 UTC | 8h 10m |
| 2026-07-25 | UAL994 | PBI → ORD | Jul 25, 22:50 UTC | Jul 26, 05:20 UTC | 6h 30m |
| 2026-07-25 | UAL125 | ATH → EWR | Jul 25, 07:45 UTC | Jul 25, 17:30 UTC | 9h 45m |
| 2026-07-24 | UAL124 | EWR → ATH | Jul 24, 20:25 UTC | Jul 25, 04:55 UTC | 8h 30m |
| 2026-07-24 | UAL65 | LIS → EWR | Jul 24, 10:55 UTC | Jul 24, 17:35 UTC | 6h 40m |
| 2026-07-24 | UAL64 | EWR → LIS | Jul 24, 01:55 UTC | Jul 24, 08:05 UTC | 6h 10m |
| 2026-07-23 | UAL1981 | DEN → LGA | Jul 23, 18:45 UTC | Jul 23, 23:15 UTC | 4h 30m |
| 2026-07-23 | UAL2445 | GSP → ORD | Jul 23, 12:00 UTC | Jul 23, 16:45 UTC | 4h 45m |
| 2026-07-23 | UAL2397 | EWR → PDX | Jul 23, 04:15 UTC | Jul 23, 08:40 UTC | 4h 25m |
| 2026-07-22 | UAL212 | DEN → SBA | Jul 22, 16:25 UTC | Jul 22, 21:20 UTC | 4h 55m |
| 2026-07-22 | UAL2303 | IAD → SAN | Jul 22, 10:20 UTC | Jul 22, 11:20 UTC | 1h 0m |
| 2026-07-21 | UAL212 | DEN → SBA | Jul 21, 23:02 UTC | Jul 22, 04:17 UTC | 5h 15m |
| 2026-07-21 | UAL212 | DEN → SBA | Jul 21, 23:25 UTC | Jul 22, 04:20 UTC | 4h 55m |
| 2026-07-21 | UAL2303 | IAD → SAN | Jul 21, 08:30 UTC | Jul 21, 13:25 UTC | 4h 55m |
| 2026-07-20 | UAL38 | HND → LAX | Jul 20, 09:45 UTC | Jul 20, 19:40 UTC | 9h 55m |
| 2026-07-19 | UAL39 | LAX → HND | Jul 19, 19:05 UTC | Jul 20, 05:30 UTC | 10h 25m |
| 2026-07-19 | UAL39 | LAX → HND | Jul 19, 19:02 UTC | Jul 20, 05:29 UTC | 10h 27m |
| 2026-07-18 | UAL2445 | - | Jul 18, 12:05 UTC | Jul 18, 16:50 UTC | 4h 45m |
| 2026-07-18 | UAL2397 | - | Jul 18, 04:25 UTC | Jul 18, 09:00 UTC | 4h 35m |
| 2026-07-18 | UAL2397 | LAX → EWR | Jul 18, 04:18 UTC | Jul 18, 08:55 UTC | 4h 37m |
| 2026-07-17 | UAL38 | HND → LAX | Jul 17, 09:45 UTC | Jul 17, 19:40 UTC | 9h 55m |
| 2026-07-16 | UAL39 | - | Jul 16, 18:50 UTC | Jul 17, 05:25 UTC | 10h 35m |
| 2026-07-14 | UAL2238 | - | Jul 14, 20:15 UTC | Jul 15, 00:50 UTC | 4h 34m |
| 2026-07-14 | UAL995 | - | Jul 14, 15:20 UTC | Jul 14, 16:30 UTC | 1h 10m |
| 2026-07-14 | UAL995 | - | Jul 14, 09:35 UTC | Jul 14, 15:15 UTC | 5h 40m |
| 2026-07-14 | UAL995 | BRU → EWR | Jul 14, 09:24 UTC | Jul 14, 16:39 UTC | 7h 15m |
| 2026-07-13 | UAL972 | ORD → BRU | Jul 13, 23:57 UTC | Jul 14, 07:18 UTC | 7h 21m |
| 2026-07-13 | UAL972 | ORD → BRU | Jul 13, 23:40 UTC | Jul 14, 07:20 UTC | 7h 40m |
| 2026-07-12 | UAL973 | - | Jul 12, 08:40 UTC | Jul 12, 10:20 UTC | 1h 40m |
| 2026-07-12 | UAL973 | BRU → ORD | Jul 12, 08:31 UTC | Jul 12, 16:24 UTC | 7h 53m |
| 2026-07-11 | UAL994 | EWR → BRU | Jul 11, 23:40 UTC | Jul 12, 06:05 UTC | 6h 25m |
| 2026-07-11 | UAL125 | ATH → EWR | Jul 11, 07:40 UTC | Jul 11, 17:25 UTC | 9h 45m |
| 2026-07-10 | UAL124 | EWR → ATH | Jul 10, 20:38 UTC | Jul 11, 04:55 UTC | 8h 17m |
| 2026-07-10 | UAL124 | EWR → ATH | Jul 10, 20:20 UTC | Jul 11, 05:01 UTC | 8h 41m |
| 2026-07-10 | UAL125 | ATH → EWR | Jul 10, 07:50 UTC | Jul 10, 17:50 UTC | 10h 0m |
| 2026-07-09 | UAL124 | - | Jul 9, 20:40 UTC | Jul 10, 05:15 UTC | 8h 35m |
| 2026-07-08 | UAL1981 | DEN → LGA | Jul 8, 18:30 UTC | Jul 8, 23:25 UTC | 4h 55m |
| 2026-07-08 | UAL2445 | - | Jul 8, 11:30 UTC | Jul 8, 16:10 UTC | 4h 40m |
| 2026-07-08 | UAL2397 | LAX → EWR | Jul 8, 04:35 UTC | Jul 8, 09:20 UTC | 4h 45m |
| 2026-07-07 | UAL2238 | - | Jul 7, 21:20 UTC | Jul 8, 02:05 UTC | 4h 45m |
| 2026-07-07 | UAL65 | LIS → EWR | Jul 7, 10:50 UTC | Jul 7, 17:55 UTC | 7h 5m |
| 2026-07-07 | UAL64 | EWR → LIS | Jul 7, 02:25 UTC | Jul 7, 08:30 UTC | 6h 5m |
| 2026-07-06 | UAL125 | - | Jul 6, 07:45 UTC | Jul 6, 17:50 UTC | 10h 5m |
| 2026-07-05 | UAL124 | EWR → ATH | Jul 5, 20:25 UTC | Jul 6, 04:45 UTC | 8h 20m |
| 2026-07-05 | UAL995 | BRU → EWR | Jul 5, 09:40 UTC | Jul 5, 17:10 UTC | 7h 30m |
| 2026-07-04 | UAL972 | - | Jul 4, 23:20 UTC | Jul 5, 06:25 UTC | 7h 5m |
| 2026-07-04 | UAL986 | - | Jul 4, 09:30 UTC | Jul 4, 17:50 UTC | 8h 20m |
| 2026-07-04 | UAL986 | CDG → ORD | Jul 4, 09:39 UTC | Jul 4, 17:34 UTC | 7h 55m |
| 2026-07-04 | UAL987 | ORD → CDG | Jul 4, 00:22 UTC | Jul 4, 07:00 UTC | 6h 38m |
| 2026-07-03 | UAL987 | - | Jul 3, 23:55 UTC | Jul 4, 07:00 UTC | 7h 5m |
About Mode-S
A Mode-S transponder code (also called an "ICAO 24-bit address" or "hex code") is a 6-character hexadecimal identifier permanently assigned to an aircraft when it's first registered. Unlike callsigns (which change with each flight) or registrations (which can change if an aircraft is sold internationally), the Mode-S address stays with the airframe for the life of the aircraft in that country.
Every ADS-B transmission from an aircraft includes its Mode-S address, making it the most reliable way to identify a specific airframe. Flight-tracking services like Apparatus use the Mode-S address as the primary key for tying position broadcasts, callsigns, and ownership records together.
Prefer a tail-number view? See the N12021 page for operator, model, and routing details .