sensors Mode-S transponder
43C8EF
ICAO 24-bit transponder address · allocated to United Kingdom
Currently assigned to ZM521 · AIRBUS HELICOPTERS EC-135/635
- Hex
- 43C8EF
- Octal
- 20744357
- Decimal
- 4,442,351
- Country
- GB
- Tail
- ZM521
- Type
- EC35
- Flights observed
- 66
- Distinct callsigns
- 20
- Country
- GB
- Last broadcast
- 22h ago
Current position
Country allocation
The ICAO 24-bit address 43C8EF falls within the block assigned to United Kingdom (GB) by ICAO Annex 10, Volume III. Every aircraft registered in United Kingdom 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 |
|---|---|---|---|
| SYS74 | - | 5 | 2026-05-27 |
| SYS38 | - | 4 | 2026-05-21 |
| SYS78 | - | 3 | 2026-06-02 |
| SYS145 | - | 3 | 2026-05-19 |
| SYS99 | - | 2 | 2026-05-12 |
| SYS84 | - | 2 | 2026-05-12 |
| SYS83 | - | 2 | 2026-06-04 |
| SYS76 | - | 2 | 2026-06-05 |
| SYS75 | - | 2 | 2026-06-10 |
| SYS71 | - | 2 | 2026-05-20 |
| SYS66 | - | 2 | 2026-05-15 |
| SYS42 | - | 2 | 2026-06-02 |
| SYS27 | - | 2 | 2026-05-22 |
| SYS21 | - | 2 | 2026-05-21 |
| SYS137 | - | 2 | 2026-05-27 |
| SYS129 | - | 2 | 2026-06-10 |
| SYS122 | - | 2 | 2026-05-13 |
| SYS97 | - | 1 | 2026-05-22 |
| SYS88 | - | 1 | 2026-06-09 |
| SYS82 | - | 1 | 2026-05-11 |
Recent flights last 50
| Date | Flight | Route | Takeoff | Landing | Duration |
|---|---|---|---|---|---|
| 2026-06-10 | SYS75 | - | Jun 10, 21:35 UTC | Jun 11, 00:40 UTC | 3h 5m |
| 2026-06-10 | SYS129 | - | Jun 10, 12:15 UTC | Jun 10, 16:00 UTC | 3h 45m |
| 2026-06-10 | SYS63 | - | Jun 10, 08:35 UTC | Jun 10, 11:45 UTC | 3h 10m |
| 2026-06-09 | SYS52 | - | Jun 9, 21:40 UTC | Jun 10, 00:45 UTC | 3h 5m |
| 2026-06-09 | SYS88 | - | Jun 9, 11:40 UTC | Jun 9, 15:15 UTC | 3h 35m |
| 2026-06-09 | SYS79 | - | Jun 9, 07:50 UTC | Jun 9, 11:00 UTC | 3h 10m |
| 2026-06-08 | SYS75 | - | Jun 8, 21:45 UTC | Jun 9, 01:00 UTC | 3h 15m |
| 2026-06-08 | SYS124 | - | Jun 8, 09:05 UTC | Jun 8, 13:15 UTC | 4h 10m |
| 2026-06-05 | SYS76 | - | Jun 5, 14:25 UTC | Jun 5, 15:40 UTC | 1h 15m |
| 2026-06-05 | SYS76 | - | Jun 5, 10:30 UTC | Jun 5, 12:35 UTC | 2h 5m |
| 2026-06-04 | SYS114 | - | Jun 4, 21:45 UTC | Jun 5, 00:55 UTC | 3h 10m |
| 2026-06-04 | SYS83 | - | Jun 4, 12:05 UTC | Jun 4, 14:05 UTC | 2h 0m |
| 2026-06-04 | SYS83 | - | Jun 4, 08:45 UTC | Jun 4, 10:10 UTC | 1h 25m |
| 2026-06-03 | SYS666 | - | Jun 3, 07:50 UTC | Jun 3, 10:40 UTC | 2h 50m |
| 2026-06-02 | SYS144 | - | Jun 2, 22:05 UTC | Jun 2, 23:35 UTC | 1h 30m |
| 2026-06-02 | SYS78 | - | Jun 2, 14:55 UTC | Jun 2, 15:25 UTC | 30m |
| 2026-06-02 | SYS78 | - | Jun 2, 13:00 UTC | Jun 2, 14:15 UTC | 1h 15m |
| 2026-06-02 | SYS42 | - | Jun 2, 08:25 UTC | Jun 2, 12:10 UTC | 3h 45m |
| 2026-06-01 | SYS56 | - | Jun 1, 14:40 UTC | Jun 1, 16:05 UTC | 1h 25m |
| 2026-06-01 | SYS31 | - | Jun 1, 09:20 UTC | Jun 1, 12:15 UTC | 2h 55m |
| 2026-05-28 | SYS112 | - | May 28, 09:20 UTC | May 28, 09:50 UTC | 30m |
| 2026-05-27 | SYS137 | - | May 27, 14:35 UTC | May 27, 15:35 UTC | 1h 0m |
| 2026-05-27 | SYS74 | - | May 27, 12:15 UTC | May 27, 13:50 UTC | 1h 35m |
| 2026-05-27 | SYS74 | - | May 27, 08:45 UTC | May 27, 10:10 UTC | 1h 25m |
| 2026-05-22 | SYS27 | - | May 22, 10:05 UTC | May 22, 11:40 UTC | 1h 35m |
| 2026-05-22 | SYS97 | - | May 22, 08:05 UTC | May 22, 08:20 UTC | 15m |
| 2026-05-21 | SYS38 | - | May 21, 14:50 UTC | May 21, 16:10 UTC | 1h 20m |
| 2026-05-21 | SYS38 | - | May 21, 12:30 UTC | May 21, 13:45 UTC | 1h 15m |
| 2026-05-21 | SYS21 | - | May 21, 10:05 UTC | May 21, 10:35 UTC | 30m |
| 2026-05-21 | SYS21 | - | May 21, 09:10 UTC | May 21, 09:30 UTC | 20m |
| 2026-05-20 | SYS71 | - | May 20, 13:50 UTC | May 20, 15:30 UTC | 1h 40m |
| 2026-05-20 | SYS38 | - | May 20, 08:35 UTC | May 20, 12:45 UTC | 4h 10m |
| 2026-05-19 | SYS145 | - | May 19, 15:40 UTC | May 19, 15:55 UTC | 15m |
| 2026-05-19 | SYS145 | - | May 19, 14:50 UTC | May 19, 15:05 UTC | 15m |
| 2026-05-19 | SYS42 | - | May 19, 12:25 UTC | May 19, 13:30 UTC | 1h 5m |
| 2026-05-19 | SYS38 | - | May 19, 09:00 UTC | May 19, 09:50 UTC | 50m |
| 2026-05-18 | SYS129 | - | May 18, 12:35 UTC | May 18, 15:30 UTC | 2h 55m |
| 2026-05-18 | SYS62 | - | May 18, 08:01 UTC | May 18, 10:35 UTC | 2h 35m |
| 2026-05-15 | SYS66 | - | May 15, 14:40 UTC | May 15, 16:40 UTC | 1h 59m |
| 2026-05-15 | SYS66 | - | May 15, 13:20 UTC | May 15, 14:35 UTC | 1h 15m |
| 2026-05-15 | SYS115 | - | May 15, 11:00 UTC | May 15, 11:10 UTC | 10m |
| 2026-05-15 | SYS78 | - | May 15, 07:55 UTC | May 15, 10:15 UTC | 2h 20m |
| 2026-05-14 | SYS02 | - | May 14, 11:45 UTC | May 14, 16:10 UTC | 4h 25m |
| 2026-05-14 | SYS59 | - | May 14, 10:45 UTC | May 14, 11:05 UTC | 20m |
| 2026-05-14 | SYS27 | - | May 14, 08:25 UTC | May 14, 09:40 UTC | 1h 15m |
| 2026-05-13 | SYS142 | - | May 13, 14:35 UTC | May 13, 15:45 UTC | 1h 10m |
| 2026-05-13 | SYS122 | - | May 13, 08:45 UTC | May 13, 10:05 UTC | 1h 20m |
| 2026-05-12 | SYS99 | - | May 12, 12:45 UTC | May 12, 14:35 UTC | 1h 50m |
| 2026-05-12 | SYS137 | - | May 12, 11:05 UTC | May 12, 12:00 UTC | 55m |
| 2026-05-12 | SYS84 | - | May 12, 08:15 UTC | May 12, 10:00 UTC | 1h 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 ZM521 page for operator, model, and routing details .