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
- 236
- Distinct callsigns
- 20
- Country
- US
- Last broadcast
- 2h 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 | - | 21 | 2026-07-09 |
| UAL857 | - | 19 | 2026-06-16 |
| UAL877 | - | 17 | 2026-07-08 |
| UAL858 | - | 14 | 2026-06-17 |
| UAL837 | United Airlines | 12 | 2026-07-05 |
| UAL810 | - | 12 | 2026-07-13 |
| UAL809 | - | 12 | 2026-07-12 |
| UAL950 | - | 10 | 2026-06-23 |
| UAL878 | - | 10 | 2026-06-30 |
| UAL989 | - | 9 | 2026-06-24 |
| UAL951 | United Airlines | 9 | 2026-06-24 |
| UAL869 | - | 9 | 2026-06-29 |
| UAL838 | - | 9 | 2026-06-18 |
| UAL872 | - | 7 | 2026-06-20 |
| UAL43 | - | 7 | 2026-06-25 |
| UAL988 | - | 6 | 2026-06-23 |
| UAL42 | - | 6 | 2026-06-23 |
| UAL190 | - | 6 | 2026-07-12 |
| UAL871 | - | 5 | 2026-06-19 |
| UAL8101 | United Airlines | 4 | 2026-04-17 |
Recent flights last 50
| Date | Flight | Route | Takeoff | Landing | Duration |
|---|---|---|---|---|---|
| 2026-07-13 | UAL810 | - | Jul 13, 13:50 UTC | Jul 14, 02:15 UTC | 12h 25m |
| 2026-07-12 | UAL809 | SFO → MNL | Jul 12, 21:43 UTC | Jul 13, 10:51 UTC | 13h 8m |
| 2026-07-12 | UAL809 | SFO → MNL | Jul 12, 21:35 UTC | Jul 13, 10:50 UTC | 13h 15m |
| 2026-07-12 | UAL190 | MNL → SFO | Jul 12, 01:01 UTC | Jul 12, 13:34 UTC | 12h 33m |
| 2026-07-12 | UAL190 | MNL → SFO | Jul 12, 01:01 UTC | Jul 12, 13:29 UTC | 12h 28m |
| 2026-07-12 | UAL190 | - | Jul 12, 01:05 UTC | Jul 12, 01:30 UTC | 25m |
| 2026-07-11 | UAL189 | - | Jul 11, 08:20 UTC | Jul 11, 21:40 UTC | 13h 20m |
| 2026-07-10 | UAL45 | - | Jul 10, 12:00 UTC | Jul 10, 23:20 UTC | 11h 20m |
| 2026-07-09 | UAL44 | SFO → ZRH | Jul 9, 21:53 UTC | Jul 10, 08:29 UTC | 10h 36m |
| 2026-07-09 | UAL44 | - | Jul 9, 22:10 UTC | Jul 10, 08:00 UTC | 9h 50m |
| 2026-07-09 | UAL862 | HKG → SFO | Jul 9, 04:15 UTC | Jul 9, 16:30 UTC | 12h 15m |
| 2026-07-08 | UAL877 | SFO → HKG | Jul 8, 07:35 UTC | Jul 8, 21:00 UTC | 13h 25m |
| 2026-07-08 | UAL2358 | SAN → EWR | Jul 8, 01:10 UTC | Jul 8, 04:40 UTC | 3h 30m |
| 2026-07-08 | UAL2358 | SAN → EWR | Jul 8, 00:33 UTC | Jul 8, 04:31 UTC | 3h 58m |
| 2026-07-07 | UAL604 | DEN → SYR | Jul 7, 18:50 UTC | Jul 7, 22:15 UTC | 3h 25m |
| 2026-07-06 | UAL1844 | EWR → SFO | Jul 6, 23:50 UTC | Jul 7, 05:00 UTC | 5h 10m |
| 2026-07-06 | UAL78 | NRT → EWR | Jul 6, 08:45 UTC | Jul 6, 20:35 UTC | 11h 50m |
| 2026-07-05 | UAL837 | SFO → NRT | Jul 5, 19:52 UTC | Jul 6, 05:33 UTC | 9h 41m |
| 2026-07-05 | UAL837 | SFO → NRT | Jul 5, 19:40 UTC | Jul 6, 05:50 UTC | 10h 10m |
| 2026-07-05 | UAL862 | HKG → SFO | Jul 5, 04:11 UTC | Jul 5, 16:06 UTC | 11h 55m |
| 2026-07-05 | UAL862 | - | Jul 5, 03:55 UTC | Jul 5, 16:10 UTC | 12h 15m |
| 2026-07-04 | UAL877 | SFO → HKG | Jul 4, 07:21 UTC | Jul 4, 20:18 UTC | 12h 57m |
| 2026-07-04 | UAL877 | - | Jul 4, 07:15 UTC | Jul 4, 19:50 UTC | 12h 35m |
| 2026-07-03 | UAL810 | - | Jul 3, 13:45 UTC | Jul 4, 01:55 UTC | 12h 10m |
| 2026-07-02 | UAL809 | - | Jul 2, 21:55 UTC | Jul 3, 10:35 UTC | 12h 40m |
| 2026-07-02 | UAL809 | SFO → MNL | Jul 2, 21:49 UTC | Jul 3, 10:30 UTC | 12h 41m |
| 2026-07-02 | UAL190 | - | Jul 2, 00:55 UTC | Jul 2, 12:45 UTC | 11h 50m |
| 2026-07-01 | UAL189 | - | Jul 1, 08:30 UTC | Jul 1, 21:20 UTC | 12h 50m |
| 2026-07-01 | UAL189 | SFO → MNL | Jul 1, 08:19 UTC | Jul 1, 21:17 UTC | 12h 58m |
| 2026-06-30 | UAL878 | HKG → SFO | Jun 30, 15:26 UTC | Jul 1, 03:50 UTC | 12h 24m |
| 2026-06-30 | UAL878 | - | Jun 30, 15:30 UTC | Jun 30, 16:45 UTC | 1h 15m |
| 2026-06-29 | UAL869 | SFO → HKG | Jun 29, 21:09 UTC | Jun 30, 10:30 UTC | 13h 21m |
| 2026-06-29 | UAL862 | - | Jun 29, 05:09 UTC | Jun 29, 16:25 UTC | 11h 15m |
| 2026-06-29 | UAL862 | - | Jun 29, 04:20 UTC | Jun 29, 04:34 UTC | 15m |
| 2026-06-28 | UAL877 | SFO → HKG | Jun 28, 07:34 UTC | Jun 28, 20:51 UTC | 13h 17m |
| 2026-06-28 | UAL877 | - | Jun 28, 07:34 UTC | Jun 28, 08:00 UTC | 25m |
| 2026-06-27 | UAL810 | - | Jun 27, 13:35 UTC | Jun 28, 01:40 UTC | 12h 5m |
| 2026-06-26 | UAL809 | SFO → MNL | Jun 26, 21:43 UTC | Jun 27, 10:55 UTC | 13h 12m |
| 2026-06-26 | UAL809 | SFO → MNL | Jun 26, 21:50 UTC | Jun 27, 11:00 UTC | 13h 10m |
| 2026-06-25 | UAL1844 | - | Jun 25, 23:09 UTC | Jun 26, 05:10 UTC | 6h 0m |
| 2026-06-25 | UAL43 | - | Jun 25, 09:34 UTC | Jun 25, 17:34 UTC | 8h 0m |
| 2026-06-24 | UAL989 | IAD → FRA | Jun 24, 22:39 UTC | Jun 25, 05:35 UTC | 6h 55m |
| 2026-06-24 | UAL951 | BRU → IAD | Jun 24, 10:25 UTC | Jun 24, 18:20 UTC | 7h 55m |
| 2026-06-23 | UAL950 | IAD → BRU | Jun 23, 23:19 UTC | Jun 24, 05:54 UTC | 6h 35m |
| 2026-06-23 | UAL988 | - | Jun 23, 10:59 UTC | Jun 23, 19:50 UTC | 8h 50m |
| 2026-06-23 | UAL42 | EWR → FRA | Jun 23, 00:00 UTC | Jun 23, 06:58 UTC | 6h 58m |
| 2026-06-23 | UAL42 | - | Jun 23, 00:00 UTC | Jun 23, 01:40 UTC | 1h 40m |
| 2026-06-22 | UAL435 | SFO → EWR | Jun 22, 15:50 UTC | Jun 22, 21:19 UTC | 5h 30m |
| 2026-06-22 | UAL435 | SFO → EWR | Jun 22, 15:39 UTC | Jun 22, 21:06 UTC | 5h 27m |
| 2026-06-22 | UAL1346 | - | Jun 22, 08:35 UTC | Jun 22, 12:59 UTC | 4h 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 .