sensors Mode-S transponder
A1F622
ICAO 24-bit transponder address · allocated to United States
Currently assigned to N2251U · BOEING 777-300ER · operated by UNITED AIRLINES INC
- Hex
- A1F622
- Octal
- 50373042
- Decimal
- 10,614,306
- Country
- US
- Tail
- N2251U
- Type
- B77W
- Flights observed
- 127
- Distinct callsigns
- 20
- Country
- US
- Last broadcast
- 3h ago
Last known position
Country allocation
The ICAO 24-bit address A1F622 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 |
|---|---|---|---|
| UAL862 | United Airlines | 12 | 2026-05-23 |
| UAL809 | United Airlines | 8 | 2026-05-20 |
| UAL877 | United Airlines | 7 | 2026-05-22 |
| UAL810 | United Airlines | 7 | 2026-05-21 |
| UAL190 | United Airlines | 7 | 2026-05-28 |
| UAL189 | United Airlines | 7 | 2026-05-29 |
| UAL857 | United Airlines | 6 | 2026-04-22 |
| UAL43 | United Airlines | 6 | 2026-05-01 |
| UAL988 | United Airlines | 5 | 2026-04-29 |
| UAL951 | United Airlines | 5 | 2026-04-30 |
| UAL878 | United Airlines | 5 | 2026-05-26 |
| UAL42 | United Airlines | 5 | 2026-04-29 |
| UAL989 | United Airlines | 4 | 2026-04-30 |
| UAL950 | United Airlines | 4 | 2026-04-29 |
| UAL858 | United Airlines | 4 | 2026-04-23 |
| UAL8250 | United Airlines | 4 | 2026-04-18 |
| UAL435 | United Airlines | 4 | 2026-04-14 |
| UAL236 | United Airlines | 4 | 2026-04-14 |
| UAL871 | United Airlines | 3 | 2026-05-24 |
| UAL869 | United Airlines | 3 | 2026-05-25 |
Recent flights last 50
| Date | Flight | Route | Takeoff | Landing | Duration |
|---|---|---|---|---|---|
| 2026-05-29 | UAL189 | CLE → PHX | May 29, 08:55 UTC | May 29, 22:30 UTC | 13h 35m |
| 2026-05-28 | UAL190 | IAH → MIA | May 28, 01:01 UTC | May 28, 13:05 UTC | 12h 4m |
| 2026-05-28 | UAL190 | IAH → MIA | May 28, 00:55 UTC | May 28, 13:10 UTC | 12h 15m |
| 2026-05-27 | UAL189 | CLE → PHX | May 27, 08:19 UTC | May 27, 21:40 UTC | 13h 21m |
| 2026-05-27 | UAL189 | CLE → PHX | May 27, 08:15 UTC | May 27, 21:45 UTC | 13h 30m |
| 2026-05-26 | UAL878 | HKG → SFO | May 26, 14:51 UTC | May 27, 02:42 UTC | 11h 51m |
| 2026-05-26 | UAL878 | HKG → SFO | May 26, 14:40 UTC | May 27, 02:29 UTC | 11h 50m |
| 2026-05-25 | UAL869 | SFO → HKG | May 25, 21:09 UTC | May 26, 10:39 UTC | 13h 30m |
| 2026-05-25 | UAL872 | TPE → SFO | May 25, 02:40 UTC | May 25, 02:55 UTC | 15m |
| 2026-05-25 | UAL872 | TPE → SFO | May 25, 02:23 UTC | May 25, 14:03 UTC | 11h 40m |
| 2026-05-24 | UAL871 | SFO → TPE | May 24, 10:30 UTC | May 24, 10:55 UTC | 25m |
| 2026-05-23 | UAL871 | SFO → TPE | May 23, 22:08 UTC | May 24, 10:48 UTC | 12h 40m |
| 2026-05-23 | UAL871 | SFO → TPE | May 23, 22:00 UTC | May 24, 09:20 UTC | 11h 20m |
| 2026-05-23 | UAL862 | HKG → SFO | May 23, 04:50 UTC | May 23, 07:35 UTC | 2h 45m |
| 2026-05-23 | UAL862 | HKG → SFO | May 23, 04:11 UTC | May 23, 15:42 UTC | 11h 31m |
| 2026-05-23 | UAL862 | HKG → SFO | May 23, 04:11 UTC | May 23, 15:44 UTC | 11h 33m |
| 2026-05-23 | UAL862 | HKG → SFO | May 23, 04:00 UTC | May 23, 04:15 UTC | 15m |
| 2026-05-22 | UAL877 | SFO → HKG | May 22, 07:25 UTC | May 22, 21:00 UTC | 13h 35m |
| 2026-05-21 | UAL810 | PHL → DEN | May 21, 14:05 UTC | May 22, 01:50 UTC | 11h 45m |
| 2026-05-20 | UAL809 | SEA → IAD | May 20, 21:42 UTC | May 21, 10:36 UTC | 12h 54m |
| 2026-05-20 | UAL809 | SEA → IAD | May 20, 21:45 UTC | May 21, 10:30 UTC | 12h 45m |
| 2026-05-20 | UAL838 | NRT → SFO | May 20, 08:15 UTC | May 20, 16:45 UTC | 8h 30m |
| 2026-05-19 | UAL837 | SFO → NRT | May 19, 19:15 UTC | May 20, 05:50 UTC | 10h 36m |
| 2026-05-19 | UAL862 | HKG → SFO | May 19, 04:11 UTC | May 19, 15:42 UTC | 11h 31m |
| 2026-05-19 | UAL862 | HKG → SFO | May 19, 04:00 UTC | May 19, 15:45 UTC | 11h 45m |
| 2026-05-18 | UAL877 | SFO → HKG | May 18, 06:55 UTC | May 18, 21:00 UTC | 14h 4m |
| 2026-05-17 | UAL190 | IAH → MIA | May 17, 00:55 UTC | May 17, 12:40 UTC | 11h 45m |
| 2026-05-16 | UAL189 | CLE → PHX | May 16, 08:16 UTC | May 16, 21:25 UTC | 13h 10m |
| 2026-05-15 | UAL810 | PHL → DEN | May 15, 13:56 UTC | May 16, 02:08 UTC | 12h 12m |
| 2026-05-15 | UAL810 | PHL → DEN | May 15, 14:15 UTC | May 16, 01:55 UTC | 11h 39m |
| 2026-05-14 | UAL809 | SEA → IAD | May 14, 21:27 UTC | May 15, 10:58 UTC | 13h 31m |
| 2026-05-14 | UAL809 | SEA → IAD | May 14, 21:40 UTC | May 15, 10:30 UTC | 12h 50m |
| 2026-05-14 | UAL838 | NRT → SFO | May 14, 08:15 UTC | May 14, 17:05 UTC | 8h 50m |
| 2026-05-13 | UAL837 | SFO → NRT | May 13, 19:05 UTC | May 14, 05:30 UTC | 10h 25m |
| 2026-05-13 | UAL837 | SFO → NRT | May 13, 19:05 UTC | May 14, 00:20 UTC | 5h 15m |
| 2026-05-13 | UAL862 | HKG → SFO | May 13, 04:11 UTC | May 13, 15:38 UTC | 11h 27m |
| 2026-05-13 | UAL862 | HKG → SFO | May 13, 03:55 UTC | May 13, 04:10 UTC | 15m |
| 2026-05-12 | UAL877 | SFO → HKG | May 12, 07:05 UTC | May 12, 20:45 UTC | 13h 40m |
| 2026-05-11 | UAL862 | HKG → SFO | May 11, 04:11 UTC | May 11, 15:33 UTC | 11h 22m |
| 2026-05-11 | UAL862 | HKG → SFO | May 11, 04:05 UTC | May 11, 15:30 UTC | 11h 25m |
| 2026-05-10 | UAL877 | SFO → HKG | May 10, 06:35 UTC | May 10, 20:28 UTC | 13h 53m |
| 2026-05-10 | UAL877 | SFO → HKG | May 10, 06:45 UTC | May 10, 07:45 UTC | 1h 0m |
| 2026-05-09 | UAL190 | IAH → MIA | May 9, 01:10 UTC | May 9, 13:15 UTC | 12h 5m |
| 2026-05-09 | UAL190 | IAH → MIA | May 9, 01:01 UTC | May 9, 13:10 UTC | 12h 9m |
| 2026-05-08 | UAL189 | CLE → PHX | May 8, 07:39 UTC | May 8, 21:30 UTC | 13h 50m |
| 2026-05-07 | UAL878 | HKG → SFO | May 7, 03:20 UTC | May 7, 03:25 UTC | 5m |
| 2026-05-06 | UAL878 | HKG → SFO | May 6, 14:51 UTC | May 7, 03:05 UTC | 12h 14m |
| 2026-05-06 | UAL878 | HKG → SFO | May 6, 14:35 UTC | May 6, 18:25 UTC | 3h 49m |
| 2026-05-05 | UAL869 | SFO → HKG | May 5, 20:32 UTC | May 6, 10:20 UTC | 13h 48m |
| 2026-05-05 | UAL869 | SFO → HKG | May 5, 20:35 UTC | May 6, 06:30 UTC | 9h 55m |
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 N2251U page for operator, model, and routing details .