sensors Mode-S transponder
A1C7C1
ICAO 24-bit transponder address · allocated to United States
Currently assigned to N2135U · BOEING 777-300ER · operated by UNITED AIRLINES INC
- Hex
- A1C7C1
- Octal
- 50343701
- Decimal
- 10,602,433
- Country
- US
- Tail
- N2135U
- Type
- B77W
- Flights observed
- 128
- Distinct callsigns
- 20
- Country
- US
- Last broadcast
- 8h ago
Current position
Country allocation
The ICAO 24-bit address A1C7C1 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 |
|---|---|---|---|
| UAL43 | United Airlines | 13 | 2026-05-26 |
| UAL872 | United Airlines | 9 | 2026-05-30 |
| UAL42 | United Airlines | 9 | 2026-05-25 |
| UAL871 | United Airlines | 8 | 2026-05-28 |
| UAL862 | United Airlines | 7 | 2026-04-26 |
| UAL1960 | United Airlines | 6 | 2026-05-12 |
| UAL1175 | United Airlines | 6 | 2026-05-22 |
| UAL869 | United Airlines | 5 | 2026-04-17 |
| UAL810 | United Airlines | 5 | 2026-05-20 |
| UAL878 | United Airlines | 4 | 2026-04-18 |
| UAL877 | United Airlines | 4 | 2026-04-25 |
| UAL2480 | United Airlines | 4 | 2026-04-28 |
| UAL2011 | United Airlines | 4 | 2026-04-16 |
| UAL201 | United Airlines | 4 | 2026-05-23 |
| UAL1777 | United Airlines | 4 | 2026-04-27 |
| UAL989 | United Airlines | 3 | 2026-05-25 |
| UAL809 | United Airlines | 3 | 2026-05-19 |
| UAL353 | United Airlines | 3 | 2026-04-15 |
| UAL2303 | United Airlines | 3 | 2026-04-15 |
| UAL200 | United Airlines | 3 | 2026-05-24 |
Recent flights last 50
| Date | Flight | Route | Takeoff | Landing | Duration |
|---|---|---|---|---|---|
| 2026-05-30 | UAL872 | TPE → SFO | May 30, 03:30 UTC | May 30, 04:40 UTC | 1h 10m |
| 2026-05-30 | UAL872 | TPE → SFO | May 30, 02:06 UTC | May 30, 02:20 UTC | 14m |
| 2026-05-28 | UAL871 | SFO → TPE | May 28, 22:08 UTC | May 29, 10:42 UTC | 12h 34m |
| 2026-05-28 | UAL871 | SFO → TPE | May 28, 22:05 UTC | May 29, 10:15 UTC | 12h 10m |
| 2026-05-26 | UAL1844 | EWR → MIA | May 26, 22:35 UTC | May 27, 03:50 UTC | 5h 15m |
| 2026-05-26 | UAL43 | OGG → EWR | May 26, 09:45 UTC | May 26, 17:25 UTC | 7h 40m |
| 2026-05-26 | UAL43 | OGG → EWR | May 26, 09:43 UTC | May 26, 17:15 UTC | 7h 32m |
| 2026-05-25 | UAL989 | IAD → FRA | May 25, 21:43 UTC | May 26, 04:42 UTC | 6h 59m |
| 2026-05-25 | UAL989 | IAD → FRA | May 25, 21:45 UTC | May 25, 23:30 UTC | 1h 45m |
| 2026-05-25 | UAL988 | FRA → IAD | May 25, 10:45 UTC | May 25, 18:50 UTC | 8h 5m |
| 2026-05-25 | UAL42 | OGG → EWR | May 25, 01:55 UTC | May 25, 07:25 UTC | 5h 30m |
| 2026-05-25 | UAL42 | OGG → EWR | May 25, 00:40 UTC | May 25, 07:10 UTC | 6h 30m |
| 2026-05-24 | UAL435 | KOA → SFO | May 24, 15:45 UTC | May 24, 20:30 UTC | 4h 45m |
| 2026-05-24 | UAL1346 | DFW → EWR | May 24, 08:20 UTC | May 24, 12:55 UTC | 4h 35m |
| 2026-05-24 | UAL200 | GUM → HNL | May 24, 03:25 UTC | May 24, 03:50 UTC | 25m |
| 2026-05-23 | UAL201 | HNL → GUM | May 23, 00:50 UTC | May 23, 01:10 UTC | 20m |
| 2026-05-22 | UAL1175 | SFO → HNL | May 22, 21:20 UTC | May 22, 21:35 UTC | 15m |
| 2026-05-22 | UAL1175 | SFO → HNL | May 22, 17:05 UTC | May 22, 17:35 UTC | 30m |
| 2026-05-22 | UAL190 | IAH → MIA | May 22, 00:55 UTC | May 22, 12:35 UTC | 11h 40m |
| 2026-05-21 | UAL189 | CLE → PHX | May 21, 08:19 UTC | May 21, 21:26 UTC | 13h 7m |
| 2026-05-21 | UAL189 | CLE → PHX | May 21, 08:10 UTC | May 21, 08:35 UTC | 25m |
| 2026-05-20 | UAL810 | PHL → DEN | May 20, 14:00 UTC | May 20, 14:25 UTC | 25m |
| 2026-05-20 | UAL810 | PHL → DEN | May 20, 13:41 UTC | May 21, 02:13 UTC | 12h 32m |
| 2026-05-19 | UAL809 | SEA → IAD | May 19, 21:30 UTC | May 20, 10:55 UTC | 13h 26m |
| 2026-05-17 | UAL506 | MSN → DEN | May 17, 13:50 UTC | May 18, 01:20 UTC | 11h 30m |
| 2026-05-17 | UAL507 | DEN → LGA | May 17, 00:15 UTC | May 17, 11:20 UTC | 11h 5m |
| 2026-05-16 | UAL1411 | SFO → EWR | May 16, 07:55 UTC | May 16, 12:21 UTC | 4h 25m |
| 2026-05-16 | UAL200 | GUM → HNL | May 16, 04:15 UTC | May 16, 04:45 UTC | 30m |
| 2026-05-15 | UAL201 | HNL → GUM | May 15, 00:30 UTC | May 15, 00:50 UTC | 20m |
| 2026-05-15 | UAL201 | HNL → GUM | May 15, 00:29 UTC | May 15, 07:25 UTC | 6h 56m |
| 2026-05-14 | UAL1175 | SFO → HNL | May 14, 21:05 UTC | May 14, 21:25 UTC | 20m |
| 2026-05-14 | UAL1175 | SFO → HNL | May 14, 16:35 UTC | May 14, 17:00 UTC | 25m |
| 2026-05-14 | UAL872 | TPE → SFO | May 14, 03:55 UTC | May 14, 12:55 UTC | 9h 0m |
| 2026-05-14 | UAL872 | TPE → SFO | May 14, 02:00 UTC | May 14, 02:15 UTC | 15m |
| 2026-05-13 | UAL871 | SFO → TPE | May 13, 10:20 UTC | May 13, 10:45 UTC | 25m |
| 2026-05-12 | UAL871 | SFO → TPE | May 12, 22:01 UTC | May 13, 09:00 UTC | 11h 0m |
| 2026-05-12 | UAL1960 | MCO → ORD | May 12, 11:30 UTC | May 12, 16:55 UTC | 5h 25m |
| 2026-05-11 | UAL41 | FCO → EWR | May 11, 16:40 UTC | May 11, 18:55 UTC | 2h 16m |
| 2026-05-10 | UAL40 | EWR → FCO | May 10, 21:40 UTC | May 11, 05:20 UTC | 7h 40m |
| 2026-05-10 | UAL43 | OGG → EWR | May 10, 09:35 UTC | May 10, 17:34 UTC | 8h 0m |
| 2026-05-10 | UAL43 | OGG → EWR | May 10, 09:31 UTC | May 10, 17:30 UTC | 7h 59m |
| 2026-05-09 | UAL989 | IAD → FRA | May 9, 22:00 UTC | May 10, 05:10 UTC | 7h 10m |
| 2026-05-09 | UAL951 | BRU → IAD | May 9, 10:25 UTC | May 9, 18:05 UTC | 7h 40m |
| 2026-05-08 | UAL950 | IAD → BRU | May 8, 22:35 UTC | May 9, 05:50 UTC | 7h 15m |
| 2026-05-08 | UAL988 | FRA → IAD | May 8, 10:29 UTC | May 8, 19:00 UTC | 8h 30m |
| 2026-05-07 | UAL42 | OGG → EWR | May 7, 23:45 UTC | May 8, 06:08 UTC | 6h 23m |
| 2026-05-07 | UAL42 | OGG → EWR | May 7, 23:39 UTC | May 8, 00:54 UTC | 1h 15m |
| 2026-05-07 | UAL1149 | EWR → SRQ | May 7, 14:35 UTC | May 7, 19:20 UTC | 4h 45m |
| 2026-05-07 | UAL1149 | EWR → SRQ | May 7, 14:34 UTC | May 7, 19:17 UTC | 4h 43m |
| 2026-05-07 | UAL1411 | SFO → EWR | May 7, 07:40 UTC | May 7, 12:10 UTC | 4h 30m |
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 N2135U page for operator, model, and routing details .