sensors Mode-S transponder
A28DC8
ICAO 24-bit transponder address · allocated to United States
Currently assigned to N2639U · BOEING 777-300ER · operated by UNITED AIRLINES INC
- Hex
- A28DC8
- Octal
- 50506710
- Decimal
- 10,653,128
- Country
- US
- Tail
- N2639U
- Type
- B77W
- Flights observed
- 136
- Distinct callsigns
- 20
- Country
- US
- Last broadcast
- 1h ago
Last known position
Country allocation
The ICAO 24-bit address A28DC8 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 | 2026-05-20 |
| UAL877 | United Airlines | 11 | 2026-05-29 |
| UAL950 | United Airlines | 9 | 2026-04-18 |
| UAL857 | United Airlines | 9 | 2026-05-26 |
| UAL810 | United Airlines | 9 | 2026-05-22 |
| UAL989 | United Airlines | 8 | 2026-04-19 |
| UAL951 | United Airlines | 8 | 2026-04-19 |
| UAL837 | United Airlines | 7 | 2026-05-21 |
| UAL838 | United Airlines | 6 | 2026-05-21 |
| UAL809 | United Airlines | 6 | 2026-05-21 |
| UAL43 | United Airlines | 6 | 2026-04-20 |
| UAL988 | United Airlines | 5 | 2026-04-18 |
| UAL878 | United Airlines | 5 | 2026-05-28 |
| UAL872 | United Airlines | 5 | 2026-05-10 |
| UAL858 | United Airlines | 5 | 2026-05-27 |
| UAL869 | United Airlines | 4 | 2026-05-27 |
| UAL8101 | United Airlines | 4 | 2026-04-17 |
| UAL42 | United Airlines | 4 | 2026-04-18 |
| UAL871 | United Airlines | 3 | 2026-05-09 |
| UAL1149 | United Airlines | 3 | 2026-04-17 |
Recent flights last 50
| Date | Flight | Route | Takeoff | Landing | Duration |
|---|---|---|---|---|---|
| 2026-05-29 | UAL877 | SFO → HKG | May 29, 22:05 UTC | May 29, 22:30 UTC | 25m |
| 2026-05-29 | UAL877 | SFO → HKG | May 29, 08:20 UTC | May 29, 08:45 UTC | 25m |
| 2026-05-29 | UAL877 | SFO → HKG | May 29, 07:40 UTC | May 29, 21:47 UTC | 14h 7m |
| 2026-05-28 | UAL878 | HKG → SFO | May 28, 14:51 UTC | May 29, 02:47 UTC | 11h 56m |
| 2026-05-28 | UAL878 | HKG → SFO | May 28, 14:45 UTC | May 28, 18:25 UTC | 3h 40m |
| 2026-05-27 | UAL869 | SFO → HKG | May 27, 21:12 UTC | May 28, 10:36 UTC | 13h 24m |
| 2026-05-27 | UAL869 | SFO → HKG | May 27, 21:10 UTC | May 28, 09:50 UTC | 12h 40m |
| 2026-05-27 | UAL858 | ICN → SFO | May 27, 05:29 UTC | May 27, 06:44 UTC | 1h 15m |
| 2026-05-27 | UAL858 | ICN → SFO | May 27, 04:44 UTC | May 27, 15:20 UTC | 10h 36m |
| 2026-05-26 | UAL857 | ICN → PVG | May 26, 06:10 UTC | May 27, 05:59 UTC | 23h 50m |
| 2026-05-25 | UAL857 | ICN → PVG | May 25, 20:57 UTC | May 26, 08:57 UTC | 12h 0m |
| 2026-05-25 | UAL857 | ICN → PVG | May 25, 20:50 UTC | May 26, 07:49 UTC | 11h 0m |
| 2026-05-25 | UAL1960 | MCO → ORD | May 25, 12:05 UTC | May 25, 17:11 UTC | 5h 6m |
| 2026-05-25 | UAL1960 | MCO → ORD | May 25, 12:00 UTC | May 25, 17:15 UTC | 5h 15m |
| 2026-05-24 | UAL78 | NRT → EWR | May 24, 08:50 UTC | May 24, 21:05 UTC | 12h 15m |
| 2026-05-23 | UAL79 | EWR → NRT | May 23, 15:55 UTC | May 24, 04:40 UTC | 12h 46m |
| 2026-05-23 | UAL2416 | LAS → SFO | May 23, 07:30 UTC | May 23, 12:15 UTC | 4h 45m |
| 2026-05-22 | UAL810 | PHL → DEN | May 22, 13:40 UTC | May 22, 17:25 UTC | 3h 45m |
| 2026-05-22 | UAL810 | PHL → DEN | May 22, 13:41 UTC | May 23, 01:23 UTC | 11h 42m |
| 2026-05-21 | UAL809 | SEA → IAD | May 21, 21:50 UTC | May 22, 10:55 UTC | 13h 5m |
| 2026-05-21 | UAL838 | NRT → SFO | May 21, 08:40 UTC | May 21, 17:20 UTC | 8h 40m |
| 2026-05-21 | UAL837 | SFO → NRT | May 21, 05:55 UTC | May 21, 06:15 UTC | 20m |
| 2026-05-20 | UAL837 | SFO → NRT | May 20, 19:05 UTC | May 21, 05:39 UTC | 10h 34m |
| 2026-05-20 | UAL837 | SFO → NRT | May 20, 19:00 UTC | May 21, 06:00 UTC | 11h 0m |
| 2026-05-20 | UAL862 | HKG → SFO | May 20, 04:55 UTC | May 20, 16:05 UTC | 11h 10m |
| 2026-05-20 | UAL862 | HKG → SFO | May 20, 04:05 UTC | May 20, 04:25 UTC | 20m |
| 2026-05-19 | UAL877 | SFO → HKG | May 19, 06:46 UTC | May 19, 20:44 UTC | 13h 58m |
| 2026-05-19 | UAL877 | SFO → HKG | May 19, 06:45 UTC | May 19, 20:55 UTC | 14h 10m |
| 2026-05-18 | UAL810 | PHL → DEN | May 18, 16:50 UTC | May 19, 01:40 UTC | 8h 49m |
| 2026-05-18 | UAL810 | PHL → DEN | May 18, 13:45 UTC | May 18, 14:05 UTC | 20m |
| 2026-05-17 | UAL809 | SEA → IAD | May 17, 21:20 UTC | May 18, 10:55 UTC | 13h 35m |
| 2026-05-17 | UAL838 | NRT → SFO | May 17, 08:30 UTC | May 17, 17:01 UTC | 8h 31m |
| 2026-05-16 | UAL837 | SFO → NRT | May 16, 19:25 UTC | May 17, 05:44 UTC | 10h 19m |
| 2026-05-16 | UAL837 | SFO → NRT | May 16, 19:15 UTC | May 16, 19:40 UTC | 25m |
| 2026-05-16 | UAL862 | HKG → SFO | May 16, 04:45 UTC | May 16, 16:05 UTC | 11h 21m |
| 2026-05-16 | UAL862 | HKG → SFO | May 16, 03:55 UTC | May 16, 04:10 UTC | 15m |
| 2026-05-15 | UAL877 | SFO → HKG | May 15, 06:45 UTC | May 15, 20:20 UTC | 13h 34m |
| 2026-05-14 | UAL810 | PHL → DEN | May 14, 13:41 UTC | May 15, 01:49 UTC | 12h 8m |
| 2026-05-14 | UAL810 | PHL → DEN | May 14, 13:40 UTC | May 15, 01:55 UTC | 12h 15m |
| 2026-05-13 | UAL809 | SEA → IAD | May 13, 21:00 UTC | May 14, 10:50 UTC | 13h 50m |
| 2026-05-13 | UAL858 | ICN → SFO | May 13, 05:25 UTC | May 13, 15:05 UTC | 9h 40m |
| 2026-05-12 | UAL857 | ICN → PVG | May 12, 06:20 UTC | May 13, 06:00 UTC | 23h 40m |
| 2026-05-11 | UAL857 | ICN → PVG | May 11, 20:50 UTC | May 12, 07:45 UTC | 10h 55m |
| 2026-05-11 | UAL838 | NRT → SFO | May 11, 08:31 UTC | May 11, 16:56 UTC | 8h 25m |
| 2026-05-11 | UAL838 | NRT → SFO | May 11, 08:10 UTC | May 11, 17:05 UTC | 8h 55m |
| 2026-05-10 | UAL837 | SFO → NRT | May 10, 19:05 UTC | May 11, 05:20 UTC | 10h 15m |
| 2026-05-10 | UAL872 | TPE → SFO | May 10, 03:25 UTC | May 10, 12:59 UTC | 9h 35m |
| 2026-05-10 | UAL872 | TPE → SFO | May 10, 02:23 UTC | May 10, 12:56 UTC | 10h 33m |
| 2026-05-10 | UAL872 | TPE → SFO | May 10, 02:00 UTC | May 10, 02:10 UTC | 10m |
| 2026-05-09 | UAL871 | SFO → TPE | May 9, 10:50 UTC | May 9, 11:15 UTC | 25m |
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 N2639U page for operator, model, and routing details .