sensors Mode-S transponder
A2551A
ICAO 24-bit transponder address · allocated to United States
Currently assigned to N24990 · BOEING 787-9 Dreamliner · operated by UNITED AIRLINES INC
- Hex
- A2551A
- Octal
- 50452432
- Decimal
- 10,638,618
- Country
- US
- Tail
- N24990
- Type
- B789
- Flights observed
- 113
- Distinct callsigns
- 20
- Country
- US
- Last broadcast
- 3h ago
Current position
Country allocation
The ICAO 24-bit address A2551A 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 |
|---|---|---|---|
| UAL820 | United Airlines | 11 | 2026-05-13 |
| UAL198 | United Airlines | 11 | 2026-05-17 |
| UAL153 | United Airlines | 11 | 2026-05-17 |
| UAL821 | United Airlines | 9 | 2026-05-13 |
| UAL152 | United Airlines | 9 | 2026-05-16 |
| UAL839 | United Airlines | 7 | 2026-05-14 |
| UAL199 | United Airlines | 7 | 2026-05-18 |
| UAL842 | United Airlines | 4 | 2026-05-15 |
| UAL892 | United Airlines | 3 | 2026-04-19 |
| UAL182 | United Airlines | 3 | 2026-05-21 |
| UAL181 | United Airlines | 3 | 2026-05-22 |
| UAL870 | United Airlines | 2 | 2026-04-18 |
| UAL63 | United Airlines | 2 | 2026-05-29 |
| UAL61 | United Airlines | 2 | 2026-04-26 |
| UAL32 | United Airlines | 2 | 2026-05-19 |
| UAL3033 | United Airlines | 2 | 2026-04-29 |
| UAL3032 | United Airlines | 2 | 2026-04-29 |
| UAL29 | United Airlines | 2 | 2026-04-23 |
| UAL28 | United Airlines | 2 | 2026-04-24 |
| UAL893 | United Airlines | 1 | 2026-04-18 |
Recent flights last 50
| Date | Flight | Route | Takeoff | Landing | Duration |
|---|---|---|---|---|---|
| 2026-05-29 | UAL7 | IAH → NRT | May 29, 15:55 UTC | May 30, 04:45 UTC | 12h 50m |
| 2026-05-29 | UAL63 | GRU → IAH | May 29, 01:15 UTC | May 29, 01:50 UTC | 35m |
| 2026-05-29 | UAL63 | GRU → IAH | May 29, 01:11 UTC | May 29, 10:55 UTC | 9h 44m |
| 2026-05-28 | UAL62 | IAH → GRU | May 28, 00:05 UTC | May 28, 09:25 UTC | 9h 20m |
| 2026-05-27 | UAL6 | NRT → IAH | May 27, 08:15 UTC | May 27, 19:50 UTC | 11h 35m |
| 2026-05-26 | UAL143 | DEN → NRT | May 26, 17:59 UTC | May 27, 05:09 UTC | 11h 10m |
| 2026-05-25 | UAL761 | MUC → DEN | May 25, 14:20 UTC | May 26, 00:35 UTC | 10h 15m |
| 2026-05-25 | UAL760 | DEN → MUC | May 25, 02:40 UTC | May 25, 11:50 UTC | 9h 10m |
| 2026-05-24 | UAL263 | EWR → PBI | May 24, 14:05 UTC | May 24, 21:45 UTC | 7h 40m |
| 2026-05-24 | UAL262 | DEN → LHR | May 24, 02:35 UTC | May 24, 10:55 UTC | 8h 20m |
| 2026-05-23 | UAL178 | KIX → GUM | May 23, 12:45 UTC | May 23, 23:30 UTC | 10h 46m |
| 2026-05-23 | UAL177 | GUM → KIX | May 23, 00:30 UTC | May 23, 10:15 UTC | 9h 44m |
| 2026-05-22 | UAL181 | FRA → DEN | May 22, 10:00 UTC | May 22, 19:40 UTC | 9h 40m |
| 2026-05-21 | UAL182 | DEN → FRA | May 21, 22:18 UTC | May 22, 06:58 UTC | 8h 40m |
| 2026-05-21 | UAL182 | DEN → FRA | May 21, 22:25 UTC | May 22, 07:10 UTC | 8h 45m |
| 2026-05-21 | UAL181 | FRA → DEN | May 21, 09:51 UTC | May 21, 19:24 UTC | 9h 33m |
| 2026-05-21 | UAL181 | FRA → DEN | May 21, 09:45 UTC | May 21, 19:25 UTC | 9h 40m |
| 2026-05-20 | UAL182 | DEN → FRA | May 20, 22:15 UTC | May 21, 06:35 UTC | 8h 20m |
| 2026-05-20 | UAL142 | NRT → DEN | May 20, 08:00 UTC | May 20, 17:40 UTC | 9h 40m |
| 2026-05-19 | UAL32 | LAX → NRT | May 19, 17:55 UTC | May 20, 05:00 UTC | 11h 6m |
| 2026-05-19 | UAL32 | LAX → NRT | May 19, 17:55 UTC | May 20, 05:01 UTC | 11h 6m |
| 2026-05-18 | UAL199 | PVG → LAX | May 18, 06:35 UTC | May 18, 23:50 UTC | 17h 14m |
| 2026-05-18 | UAL199 | PVG → LAX | May 18, 01:50 UTC | May 18, 23:50 UTC | 21h 59m |
| 2026-05-17 | UAL198 | LAX → PVG | May 17, 20:35 UTC | May 18, 15:20 UTC | 18h 45m |
| 2026-05-17 | UAL198 | LAX → PVG | May 17, 20:18 UTC | May 18, 09:12 UTC | 12h 54m |
| 2026-05-17 | UAL198 | LAX → PVG | May 17, 20:15 UTC | May 18, 15:20 UTC | 19h 5m |
| 2026-05-17 | UAL153 | HKG → LAX | May 17, 05:10 UTC | May 17, 17:35 UTC | 12h 25m |
| 2026-05-17 | UAL153 | HKG → LAX | May 17, 00:19 UTC | May 17, 02:30 UTC | 2h 11m |
| 2026-05-16 | UAL152 | LAX → HKG | May 16, 13:21 UTC | May 16, 13:35 UTC | 15m |
| 2026-05-16 | UAL152 | LAX → HKG | May 16, 12:49 UTC | May 16, 15:21 UTC | 2h 32m |
| 2026-05-15 | UAL152 | LAX → HKG | May 15, 19:20 UTC | May 16, 10:01 UTC | 14h 41m |
| 2026-05-15 | UAL842 | SYD → LAX | May 15, 00:00 UTC | May 15, 13:10 UTC | 13h 10m |
| 2026-05-14 | UAL839 | LAX → SYD | May 14, 06:40 UTC | May 14, 07:05 UTC | 25m |
| 2026-05-14 | UAL839 | LAX → SYD | May 14, 06:04 UTC | May 14, 20:55 UTC | 14h 51m |
| 2026-05-13 | UAL821 | SFO → MEX | May 13, 14:20 UTC | May 14, 02:40 UTC | 12h 20m |
| 2026-05-13 | UAL821 | SFO → MEX | May 13, 10:45 UTC | May 13, 11:00 UTC | 15m |
| 2026-05-13 | UAL821 | SFO → MEX | May 13, 08:50 UTC | May 13, 09:30 UTC | 40m |
| 2026-05-13 | UAL820 | MEX → SFO | May 13, 01:45 UTC | May 13, 02:25 UTC | 40m |
| 2026-05-13 | UAL820 | MEX → SFO | May 13, 00:05 UTC | May 13, 00:20 UTC | 15m |
| 2026-05-13 | UAL820 | MEX → SFO | May 13, 00:01 UTC | May 13, 02:20 UTC | 2h 19m |
| 2026-05-12 | UAL820 | MEX → SFO | May 12, 06:50 UTC | May 12, 21:50 UTC | 15h 0m |
| 2026-05-12 | UAL820 | MEX → SFO | May 12, 06:19 UTC | May 12, 21:49 UTC | 15h 30m |
| 2026-05-11 | UAL199 | PVG → LAX | May 11, 13:20 UTC | May 11, 14:40 UTC | 1h 20m |
| 2026-05-11 | UAL199 | PVG → LAX | May 11, 12:31 UTC | May 11, 23:41 UTC | 11h 10m |
| 2026-05-11 | UAL198 | LAX → PVG | May 11, 00:34 UTC | May 11, 22:35 UTC | 22h 0m |
| 2026-05-11 | UAL198 | LAX → PVG | May 11, 00:19 UTC | May 11, 22:15 UTC | 21h 56m |
| 2026-05-10 | UAL198 | LAX → PVG | May 10, 20:35 UTC | May 11, 14:40 UTC | 18h 5m |
| 2026-05-10 | UAL198 | LAX → PVG | May 10, 20:00 UTC | May 10, 20:30 UTC | 30m |
| 2026-05-10 | UAL198 | LAX → PVG | May 10, 20:08 UTC | May 11, 08:51 UTC | 12h 43m |
| 2026-05-10 | UAL153 | HKG → LAX | May 10, 05:45 UTC | May 10, 06:04 UTC | 20m |
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 N24990 page for operator, model, and routing details .