sensors Mode-S transponder
A31A57
ICAO 24-bit transponder address · allocated to United States
Currently assigned to N29978 · BOEING 787-9 Dreamliner · operated by UNITED AIRLINES INC
- Hex
- A31A57
- Octal
- 50615127
- Decimal
- 10,689,111
- Country
- US
- Tail
- N29978
- Type
- B789
- Flights observed
- 213
- Distinct callsigns
- 20
- Country
- US
- Last broadcast
- Jul 19, 02:00 UTC
Last known position
Country allocation
The ICAO 24-bit address A31A57 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 |
|---|---|---|---|
| UAL821 | - | 16 | 2026-06-30 |
| UAL893 | - | 15 | 2026-06-12 |
| UAL820 | United Airlines | 15 | 2026-07-18 |
| UAL29 | - | 15 | 2026-07-07 |
| UAL28 | - | 14 | 2026-07-08 |
| UAL892 | United Airlines | 13 | 2026-06-13 |
| UAL152 | - | 11 | 2026-07-13 |
| UAL60 | United Airlines | 10 | 2026-06-11 |
| UAL153 | - | 10 | 2026-07-17 |
| UAL935 | - | 7 | 2026-07-10 |
| UAL870 | - | 7 | 2026-07-07 |
| UAL839 | - | 7 | 2026-07-01 |
| UAL61 | United Airlines | 6 | 2026-06-12 |
| UAL199 | - | 6 | 2026-07-15 |
| UAL115 | United Airlines | 6 | 2026-05-31 |
| UAL198 | - | 5 | 2026-07-14 |
| UAL114 | United Airlines | 5 | 2026-06-01 |
| UAL923 | United Airlines | 4 | 2026-05-19 |
| UAL863 | - | 4 | 2026-07-06 |
| UAL842 | - | 4 | 2026-06-27 |
Recent flights last 50
| Date | Flight | Route | Takeoff | Landing | Duration |
|---|---|---|---|---|---|
| 2026-07-19 | UAL3879 | - | Jul 19, 01:50 UTC | Jul 19, 02:00 UTC | 10m |
| 2026-07-18 | UAL820 | MEX → SFO | Jul 18, 07:55 UTC | Jul 18, 21:15 UTC | 13h 20m |
| 2026-07-18 | UAL820 | MEX → SFO | Jul 18, 07:14 UTC | Jul 18, 21:16 UTC | 14h 2m |
| 2026-07-17 | UAL153 | - | Jul 17, 05:04 UTC | Jul 17, 18:29 UTC | 13h 25m |
| 2026-07-17 | UAL153 | HKG → LAX | Jul 17, 05:08 UTC | Jul 17, 18:29 UTC | 13h 21m |
| 2026-07-16 | UAL820 | - | Jul 16, 07:30 UTC | Jul 16, 21:10 UTC | 13h 40m |
| 2026-07-15 | UAL199 | PVG → LAX | Jul 15, 12:31 UTC | Jul 15, 23:44 UTC | 11h 13m |
| 2026-07-15 | UAL199 | - | Jul 15, 06:30 UTC | Jul 15, 23:50 UTC | 17h 20m |
| 2026-07-14 | UAL198 | - | Jul 14, 20:50 UTC | Jul 15, 14:55 UTC | 18h 4m |
| 2026-07-14 | UAL153 | HKG → LAX | Jul 14, 05:08 UTC | Jul 14, 18:14 UTC | 13h 6m |
| 2026-07-14 | UAL153 | - | Jul 14, 05:05 UTC | Jul 14, 08:55 UTC | 3h 50m |
| 2026-07-14 | UAL153 | - | Jul 14, 02:30 UTC | Jul 14, 02:35 UTC | 5m |
| 2026-07-13 | UAL152 | - | Jul 13, 12:50 UTC | Jul 13, 13:00 UTC | 10m |
| 2026-07-13 | UAL152 | - | Jul 13, 09:55 UTC | Jul 13, 10:15 UTC | 20m |
| 2026-07-12 | UAL152 | - | Jul 12, 20:15 UTC | Jul 13, 09:20 UTC | 13h 5m |
| 2026-07-12 | UAL33 | - | Jul 12, 08:01 UTC | Jul 12, 17:35 UTC | 9h 35m |
| 2026-07-11 | UAL32 | LAX → NRT | Jul 11, 18:10 UTC | Jul 12, 04:40 UTC | 10h 30m |
| 2026-07-10 | UAL935 | - | Jul 10, 12:40 UTC | Jul 10, 23:05 UTC | 10h 25m |
| 2026-07-10 | UAL935 | LHR → LAX | Jul 10, 12:30 UTC | Jul 10, 23:04 UTC | 10h 34m |
| 2026-07-10 | UAL948 | - | Jul 10, 00:40 UTC | Jul 10, 10:15 UTC | 9h 35m |
| 2026-07-08 | UAL28 | - | Jul 8, 17:30 UTC | Jul 9, 04:55 UTC | 11h 25m |
| 2026-07-07 | UAL29 | SFO → SIN | Jul 7, 20:00 UTC | Jul 8, 11:58 UTC | 15h 58m |
| 2026-07-07 | UAL29 | - | Jul 7, 20:10 UTC | Jul 8, 10:20 UTC | 14h 10m |
| 2026-07-07 | UAL870 | SYD → SFO | Jul 7, 01:00 UTC | Jul 7, 13:40 UTC | 12h 40m |
| 2026-07-06 | UAL863 | - | Jul 6, 07:55 UTC | Jul 6, 21:45 UTC | 13h 50m |
| 2026-07-06 | UAL863 | SFO → SYD | Jul 6, 06:46 UTC | Jul 6, 22:23 UTC | 15h 37m |
| 2026-07-05 | UAL806 | ICN → SFO | Jul 5, 02:56 UTC | Jul 5, 12:55 UTC | 9h 59m |
| 2026-07-05 | UAL806 | - | Jul 5, 02:40 UTC | Jul 5, 04:25 UTC | 1h 45m |
| 2026-07-04 | UAL805 | SFO → ICN | Jul 4, 08:51 UTC | Jul 4, 20:09 UTC | 11h 18m |
| 2026-07-04 | UAL805 | SFO → ICN | Jul 4, 08:55 UTC | Jul 4, 20:15 UTC | 11h 20m |
| 2026-07-03 | UAL28 | - | Jul 3, 14:50 UTC | Jul 4, 04:45 UTC | 13h 55m |
| 2026-07-03 | UAL28 | SIN → SFO | Jul 3, 13:20 UTC | Jul 4, 04:45 UTC | 15h 25m |
| 2026-07-02 | UAL29 | - | Jul 2, 19:15 UTC | Jul 2, 19:40 UTC | 25m |
| 2026-07-02 | UAL870 | - | Jul 2, 01:20 UTC | Jul 2, 14:00 UTC | 12h 40m |
| 2026-07-01 | UAL839 | - | Jul 1, 06:25 UTC | Jul 1, 06:50 UTC | 25m |
| 2026-07-01 | UAL839 | LAX → SYD | Jul 1, 06:19 UTC | Jul 1, 21:00 UTC | 14h 41m |
| 2026-06-30 | UAL821 | - | Jun 30, 15:00 UTC | Jul 1, 03:05 UTC | 12h 5m |
| 2026-06-30 | UAL821 | HKG → LAX | Jun 30, 14:06 UTC | Jul 1, 02:59 UTC | 12h 53m |
| 2026-06-30 | UAL821 | - | Jun 30, 14:10 UTC | Jun 30, 14:25 UTC | 15m |
| 2026-06-30 | UAL821 | - | Jun 30, 09:15 UTC | Jun 30, 09:40 UTC | 25m |
| 2026-06-30 | UAL821 | BKK → HKG | Jun 30, 09:05 UTC | Jun 30, 11:33 UTC | 2h 28m |
| 2026-06-30 | UAL820 | - | Jun 30, 01:04 UTC | Jun 30, 02:25 UTC | 1h 21m |
| 2026-06-30 | UAL820 | - | Jun 30, 00:14 UTC | Jun 30, 00:25 UTC | 10m |
| 2026-06-29 | UAL820 | - | Jun 29, 07:30 UTC | Jun 29, 21:39 UTC | 14h 10m |
| 2026-06-28 | UAL353 | - | Jun 28, 23:09 UTC | Jun 29, 04:00 UTC | 4h 50m |
| 2026-06-28 | UAL2096 | LAX → EWR | Jun 28, 16:25 UTC | Jun 28, 21:14 UTC | 4h 50m |
| 2026-06-27 | UAL842 | SYD → LAX | Jun 27, 23:51 UTC | Jun 28, 12:54 UTC | 13h 3m |
| 2026-06-27 | UAL842 | - | Jun 27, 23:55 UTC | Jun 28, 00:39 UTC | 45m |
| 2026-06-27 | UAL839 | - | Jun 27, 06:09 UTC | Jun 27, 20:39 UTC | 14h 30m |
| 2026-06-26 | UAL821 | HKG → LAX | Jun 26, 14:06 UTC | Jun 27, 03:04 UTC | 12h 58m |
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 N29978 page for operator, model, and routing details .