sensors Mode-S transponder
A254FF
ICAO 24-bit transponder address · allocated to United States
Currently assigned to N24988 · BOEING 787-9 Dreamliner · operated by UNITED AIRLINES INC
- Hex
- A254FF
- Octal
- 50452377
- Decimal
- 10,638,591
- Country
- US
- Tail
- N24988
- Type
- B789
- Flights observed
- 182
- Distinct callsigns
- 20
- Country
- US
- Last broadcast
- 12h ago
Current position
Country allocation
The ICAO 24-bit address A254FF 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 |
|---|---|---|---|
| UAL863 | - | 10 | 2026-07-10 |
| UAL187 | - | 9 | 2026-06-26 |
| UAL1011 | United Airlines | 9 | 2026-05-31 |
| UAL2023 | United Airlines | 8 | 2026-06-01 |
| UAL893 | United Airlines | 6 | 2026-05-01 |
| UAL188 | United Airlines | 6 | 2026-06-26 |
| UAL1849 | United Airlines | 6 | 2026-06-29 |
| UAL1757 | - | 6 | 2026-06-29 |
| UAL892 | United Airlines | 5 | 2026-05-02 |
| UAL870 | United Airlines | 5 | 2026-07-18 |
| UAL806 | - | 5 | 2026-06-25 |
| UAL805 | - | 5 | 2026-06-24 |
| UAL60 | United Airlines | 5 | 2026-05-03 |
| UAL199 | - | 5 | 2026-07-16 |
| UAL198 | - | 5 | 2026-07-15 |
| UAL83 | United Airlines | 4 | 2026-07-06 |
| UAL61 | United Airlines | 4 | 2026-05-04 |
| UAL1593 | United Airlines | 4 | 2026-06-12 |
| UAL123 | - | 4 | 2026-07-08 |
| UAL839 | - | 3 | 2026-07-17 |
Recent flights last 50
| Date | Flight | Route | Takeoff | Landing | Duration |
|---|---|---|---|---|---|
| 2026-07-18 | UAL870 | SYD → SFO | Jul 18, 00:45 UTC | Jul 18, 13:35 UTC | 12h 50m |
| 2026-07-18 | UAL870 | SYD → SFO | Jul 18, 00:35 UTC | Jul 18, 01:15 UTC | 40m |
| 2026-07-17 | UAL839 | - | Jul 17, 21:34 UTC | Jul 17, 21:39 UTC | 5m |
| 2026-07-17 | UAL839 | - | Jul 17, 07:14 UTC | Jul 17, 07:50 UTC | 35m |
| 2026-07-17 | UAL839 | LAX → SYD | Jul 17, 06:24 UTC | Jul 17, 21:15 UTC | 14h 51m |
| 2026-07-16 | UAL199 | PVG → LAX | Jul 16, 12:31 UTC | Jul 16, 23:54 UTC | 11h 23m |
| 2026-07-16 | UAL199 | - | Jul 16, 06:15 UTC | Jul 17, 00:04 UTC | 17h 50m |
| 2026-07-15 | UAL198 | - | Jul 15, 20:35 UTC | Jul 16, 14:55 UTC | 18h 20m |
| 2026-07-15 | UAL33 | - | Jul 15, 08:05 UTC | Jul 15, 17:35 UTC | 9h 30m |
| 2026-07-15 | UAL33 | NRT → LAX | Jul 15, 08:05 UTC | Jul 15, 17:26 UTC | 9h 21m |
| 2026-07-14 | UAL7 | - | Jul 14, 16:15 UTC | Jul 15, 04:50 UTC | 12h 34m |
| 2026-07-14 | UAL63 | - | Jul 14, 01:05 UTC | Jul 14, 10:45 UTC | 9h 40m |
| 2026-07-13 | UAL62 | - | Jul 13, 00:01 UTC | Jul 13, 09:30 UTC | 9h 30m |
| 2026-07-12 | UAL6 | - | Jul 12, 09:05 UTC | Jul 12, 09:35 UTC | 30m |
| 2026-07-12 | UAL6 | NRT → IAH | Jul 12, 09:01 UTC | Jul 12, 20:15 UTC | 11h 14m |
| 2026-07-11 | UAL143 | DEN → NRT | Jul 11, 19:40 UTC | Jul 12, 06:45 UTC | 11h 5m |
| 2026-07-11 | UAL3938 | - | Jul 11, 16:10 UTC | Jul 11, 18:05 UTC | 1h 55m |
| 2026-07-11 | UAL3938 | LAX → DEN | Jul 11, 15:59 UTC | Jul 11, 18:04 UTC | 2h 5m |
| 2026-07-10 | UAL842 | SYD → LAX | Jul 10, 23:50 UTC | Jul 11, 13:05 UTC | 13h 15m |
| 2026-07-10 | UAL863 | SFO → SYD | Jul 10, 06:45 UTC | Jul 10, 20:48 UTC | 14h 3m |
| 2026-07-10 | UAL863 | - | Jul 10, 06:45 UTC | Jul 10, 19:45 UTC | 13h 0m |
| 2026-07-08 | UAL1227 | EWR → SFO | Jul 8, 17:55 UTC | Jul 8, 23:05 UTC | 5h 10m |
| 2026-07-08 | UAL123 | LHR → EWR | Jul 8, 06:55 UTC | Jul 8, 13:55 UTC | 7h 0m |
| 2026-07-08 | UAL123 | LHR → EWR | Jul 8, 07:02 UTC | Jul 8, 13:57 UTC | 6h 55m |
| 2026-07-07 | UAL122 | EWR → LHR | Jul 7, 14:10 UTC | Jul 7, 20:30 UTC | 6h 20m |
| 2026-07-06 | UAL83 | DEL → EWR | Jul 6, 18:40 UTC | Jul 7, 05:45 UTC | 11h 5m |
| 2026-07-06 | UAL83 | DEL → EWR | Jul 6, 18:32 UTC | Jul 7, 10:24 UTC | 15h 52m |
| 2026-07-06 | UAL83 | DEL → EWR | Jul 6, 18:32 UTC | Jul 7, 10:19 UTC | 15h 47m |
| 2026-07-06 | UAL82 | EWR → DEL | Jul 6, 02:07 UTC | Jul 6, 16:28 UTC | 14h 21m |
| 2026-07-06 | UAL82 | - | Jul 6, 02:50 UTC | Jul 6, 16:15 UTC | 13h 25m |
| 2026-07-04 | UAL83 | DEL → EWR | Jul 4, 18:45 UTC | Jul 5, 10:35 UTC | 15h 50m |
| 2026-07-04 | UAL82 | - | Jul 4, 02:55 UTC | Jul 4, 16:10 UTC | 13h 15m |
| 2026-07-03 | UAL1173 | SJU → EWR | Jul 3, 20:00 UTC | Jul 3, 21:10 UTC | 1h 10m |
| 2026-07-03 | UAL1173 | SJU → EWR | Jul 3, 17:35 UTC | Jul 3, 17:50 UTC | 15m |
| 2026-07-03 | UAL1173 | SJU → EWR | Jul 3, 17:39 UTC | Jul 3, 21:04 UTC | 3h 25m |
| 2026-07-03 | UAL2143 | - | Jul 3, 15:00 UTC | Jul 3, 15:25 UTC | 25m |
| 2026-07-03 | UAL2143 | - | Jul 3, 12:15 UTC | Jul 3, 12:55 UTC | 40m |
| 2026-07-02 | UAL2222 | - | Jul 2, 18:10 UTC | Jul 3, 07:45 UTC | 13h 35m |
| 2026-07-02 | UAL2222 | CPT → EWR | Jul 2, 18:12 UTC | Jul 3, 08:46 UTC | 14h 34m |
| 2026-07-02 | UAL1122 | - | Jul 2, 01:10 UTC | Jul 2, 14:40 UTC | 13h 30m |
| 2026-07-01 | UAL2096 | LAX → EWR | Jul 1, 16:15 UTC | Jul 1, 20:55 UTC | 4h 40m |
| 2026-07-01 | UAL842 | - | Jul 1, 00:35 UTC | Jul 1, 13:05 UTC | 12h 30m |
| 2026-06-30 | UAL863 | SFO → SYD | Jun 30, 06:31 UTC | Jun 30, 20:46 UTC | 14h 15m |
| 2026-06-30 | UAL863 | SFO → SYD | Jun 30, 06:40 UTC | Jun 30, 20:50 UTC | 14h 10m |
| 2026-06-29 | UAL1757 | - | Jun 29, 22:24 UTC | Jun 30, 03:20 UTC | 4h 56m |
| 2026-06-29 | UAL1849 | MCO → EWR | Jun 29, 15:24 UTC | Jun 29, 19:49 UTC | 4h 25m |
| 2026-06-28 | UAL1227 | EWR → SFO | Jun 28, 18:07 UTC | Jun 28, 23:33 UTC | 5h 26m |
| 2026-06-28 | UAL1227 | EWR → SFO | Jun 28, 18:14 UTC | Jun 28, 23:34 UTC | 5h 20m |
| 2026-06-28 | UAL123 | - | Jun 28, 06:55 UTC | Jun 28, 13:45 UTC | 6h 50m |
| 2026-06-28 | UAL123 | LHR → EWR | Jun 28, 07:02 UTC | Jun 28, 13:47 UTC | 6h 45m |
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 N24988 page for operator, model, and routing details .