sensors Mode-S transponder
A21656
ICAO 24-bit transponder address · allocated to United States
Currently assigned to N2332U · BOEING 777-300ER · operated by UNITED AIRLINES INC
- Hex
- A21656
- Octal
- 50413126
- Decimal
- 10,622,550
- Country
- US
- Tail
- N2332U
- Type
- B77W
- Flights observed
- 239
- Distinct callsigns
- 20
- Country
- US
- Last broadcast
- Jul 26, 20:25 UTC
Last known position
Country allocation
The ICAO 24-bit address A21656 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 |
|---|---|---|---|
| UAL857 | United Airlines | 21 | 2026-07-25 |
| UAL858 | United Airlines | 18 | 2026-07-26 |
| UAL950 | - | 15 | 2026-07-15 |
| UAL951 | - | 13 | 2026-07-16 |
| UAL872 | - | 13 | 2026-06-26 |
| UAL871 | - | 12 | 2026-06-25 |
| UAL43 | - | 10 | 2026-07-17 |
| UAL42 | - | 10 | 2026-07-15 |
| UAL989 | - | 9 | 2026-07-16 |
| UAL869 | - | 9 | 2026-07-10 |
| UAL838 | - | 9 | 2026-07-07 |
| UAL837 | United Airlines | 9 | 2026-07-26 |
| UAL1175 | - | 9 | 2026-07-12 |
| UAL988 | - | 8 | 2026-07-15 |
| UAL862 | - | 7 | 2026-07-10 |
| UAL1960 | United Airlines | 7 | 2026-07-24 |
| UAL878 | - | 6 | 2026-07-11 |
| UAL79 | - | 5 | 2026-07-02 |
| UAL78 | United Airlines | 5 | 2026-07-23 |
| UAL877 | - | 4 | 2026-07-09 |
Recent flights last 50
| Date | Flight | Route | Takeoff | Landing | Duration |
|---|---|---|---|---|---|
| 2026-07-26 | UAL837 | SFO → NRT | Jul 26, 19:55 UTC | Jul 26, 20:25 UTC | 30m |
| 2026-07-26 | UAL858 | ICN → SFO | Jul 26, 05:10 UTC | Jul 26, 06:50 UTC | 1h 41m |
| 2026-07-26 | UAL858 | ICN → SFO | Jul 26, 04:44 UTC | Jul 26, 15:02 UTC | 10h 18m |
| 2026-07-25 | UAL858 | ICN → SFO | Jul 25, 07:35 UTC | Jul 26, 06:50 UTC | 23h 16m |
| 2026-07-25 | UAL857 | ICN → PVG | Jul 25, 06:05 UTC | Jul 26, 05:30 UTC | 23h 25m |
| 2026-07-24 | UAL857 | ICN → PVG | Jul 24, 20:57 UTC | Jul 25, 08:45 UTC | 11h 48m |
| 2026-07-24 | UAL857 | ICN → PVG | Jul 24, 21:05 UTC | Jul 25, 08:00 UTC | 10h 55m |
| 2026-07-24 | UAL1960 | MCO → ORD | Jul 24, 11:20 UTC | Jul 24, 16:35 UTC | 5h 15m |
| 2026-07-23 | UAL78 | NRT → EWR | Jul 23, 08:40 UTC | Jul 23, 20:15 UTC | 11h 35m |
| 2026-07-22 | UAL837 | SFO → NRT | Jul 22, 20:20 UTC | Jul 23, 06:00 UTC | 9h 40m |
| 2026-07-19 | UAL2328 | - | Jul 19, 20:20 UTC | Jul 20, 01:20 UTC | 5h 0m |
| 2026-07-19 | UAL2328 | EWR → SFO | Jul 19, 19:55 UTC | Jul 20, 01:15 UTC | 5h 20m |
| 2026-07-18 | UAL41 | - | Jul 18, 09:40 UTC | Jul 18, 12:20 UTC | 2h 40m |
| 2026-07-18 | UAL41 | FCO → EWR | Jul 18, 09:27 UTC | Jul 18, 18:05 UTC | 8h 38m |
| 2026-07-17 | UAL40 | EWR → FCO | Jul 17, 21:48 UTC | Jul 18, 05:16 UTC | 7h 28m |
| 2026-07-17 | UAL40 | - | Jul 17, 21:39 UTC | Jul 17, 23:14 UTC | 1h 35m |
| 2026-07-17 | UAL43 | - | Jul 17, 09:55 UTC | Jul 17, 11:50 UTC | 1h 55m |
| 2026-07-17 | UAL43 | FRA → EWR | Jul 17, 09:51 UTC | Jul 17, 17:30 UTC | 7h 39m |
| 2026-07-16 | UAL989 | IAD → FRA | Jul 16, 21:43 UTC | Jul 17, 04:44 UTC | 7h 1m |
| 2026-07-16 | UAL989 | - | Jul 16, 21:35 UTC | Jul 16, 23:25 UTC | 1h 50m |
| 2026-07-16 | UAL951 | BRU → IAD | Jul 16, 11:05 UTC | Jul 16, 18:34 UTC | 7h 30m |
| 2026-07-15 | UAL950 | IAD → BRU | Jul 15, 22:43 UTC | Jul 16, 06:08 UTC | 7h 25m |
| 2026-07-15 | UAL950 | - | Jul 15, 22:55 UTC | Jul 16, 06:10 UTC | 7h 15m |
| 2026-07-15 | UAL988 | FRA → IAD | Jul 15, 11:10 UTC | Jul 15, 19:45 UTC | 8h 35m |
| 2026-07-15 | UAL42 | EWR → FRA | Jul 15, 00:00 UTC | Jul 15, 06:57 UTC | 6h 57m |
| 2026-07-15 | UAL42 | - | Jul 15, 00:00 UTC | Jul 15, 07:05 UTC | 7h 5m |
| 2026-07-14 | UAL435 | SFO → EWR | Jul 14, 16:00 UTC | Jul 14, 20:55 UTC | 4h 55m |
| 2026-07-14 | UAL1346 | - | Jul 14, 08:35 UTC | Jul 14, 12:50 UTC | 4h 15m |
| 2026-07-14 | UAL200 | - | Jul 14, 03:55 UTC | Jul 14, 04:15 UTC | 20m |
| 2026-07-13 | UAL200 | GUM → HNL | Jul 13, 21:18 UTC | Jul 14, 04:21 UTC | 7h 3m |
| 2026-07-13 | UAL201 | - | Jul 13, 00:50 UTC | Jul 13, 01:01 UTC | 10m |
| 2026-07-13 | UAL201 | HNL → GUM | Jul 13, 00:49 UTC | Jul 13, 07:49 UTC | 7h 0m |
| 2026-07-12 | UAL1175 | - | Jul 12, 16:35 UTC | Jul 12, 21:10 UTC | 4h 35m |
| 2026-07-12 | UAL1175 | SFO → HNL | Jul 12, 16:43 UTC | Jul 12, 21:09 UTC | 4h 26m |
| 2026-07-11 | UAL878 | - | Jul 11, 15:45 UTC | Jul 12, 03:50 UTC | 12h 5m |
| 2026-07-11 | UAL878 | - | Jul 11, 14:50 UTC | Jul 11, 15:05 UTC | 15m |
| 2026-07-10 | UAL869 | SFO → HKG | Jul 10, 21:42 UTC | Jul 11, 11:49 UTC | 14h 7m |
| 2026-07-10 | UAL869 | - | Jul 10, 21:50 UTC | Jul 10, 22:20 UTC | 30m |
| 2026-07-10 | UAL862 | HKG → SFO | Jul 10, 04:11 UTC | Jul 10, 16:15 UTC | 12h 4m |
| 2026-07-10 | UAL862 | - | Jul 10, 04:10 UTC | Jul 10, 08:00 UTC | 3h 50m |
| 2026-07-09 | UAL877 | SFO → HKG | Jul 9, 07:41 UTC | Jul 9, 20:51 UTC | 13h 10m |
| 2026-07-09 | UAL877 | SFO → HKG | Jul 9, 07:35 UTC | Jul 9, 21:00 UTC | 13h 25m |
| 2026-07-08 | UAL878 | - | Jul 8, 14:55 UTC | Jul 9, 03:00 UTC | 12h 5m |
| 2026-07-07 | UAL869 | - | Jul 7, 21:25 UTC | Jul 8, 10:45 UTC | 13h 20m |
| 2026-07-07 | UAL838 | - | Jul 7, 08:25 UTC | Jul 7, 17:20 UTC | 8h 55m |
| 2026-07-06 | UAL837 | SFO → NRT | Jul 6, 19:45 UTC | Jul 7, 06:00 UTC | 10h 15m |
| 2026-07-06 | UAL862 | HKG → SFO | Jul 6, 04:11 UTC | Jul 6, 16:23 UTC | 12h 12m |
| 2026-07-06 | UAL862 | - | Jul 6, 04:00 UTC | Jul 6, 16:25 UTC | 12h 25m |
| 2026-07-05 | UAL877 | - | Jul 5, 07:20 UTC | Jul 5, 20:30 UTC | 13h 10m |
| 2026-07-04 | UAL878 | HKG → SFO | Jul 4, 15:00 UTC | Jul 5, 03:05 UTC | 12h 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 N2332U page for operator, model, and routing details .