sensors Mode-S transponder
4B1E21
ICAO 24-bit transponder address · allocated to Switzerland
- Hex
- 4B1E21
- Octal
- 22617041
- Decimal
- 4,922,913
- Country
- CH
- Flights observed
- 28
- Distinct callsigns
- 1
- Country
- CH
- Last broadcast
- 1d ago
Last known position
Country allocation
The ICAO 24-bit address 4B1E21 falls within the block assigned to Switzerland (CH) by ICAO Annex 10, Volume III. Every aircraft registered in Switzerland 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 1 distinct
| Callsign | Airline | Flights | Last seen |
|---|---|---|---|
| HBLKR | - | 28 | 2026-07-23 |
Recent flights last 28
| Date | Flight | Route | Takeoff | Landing | Duration |
|---|---|---|---|---|---|
| 2026-07-23 | HBLKR | - | Jul 23, 12:35 UTC | Jul 23, 13:20 UTC | 45m |
| 2026-07-23 | HBLKR | - | Jul 23, 05:45 UTC | Jul 23, 06:25 UTC | 40m |
| 2026-07-21 | HBLKR | - | Jul 21, 09:55 UTC | Jul 21, 10:35 UTC | 40m |
| 2026-07-21 | HBLKR | - | Jul 21, 06:20 UTC | Jul 21, 07:10 UTC | 50m |
| 2026-07-18 | HBLKR | - | Jul 18, 11:55 UTC | Jul 18, 13:10 UTC | 1h 15m |
| 2026-07-18 | HBLKR | - | Jul 18, 09:00 UTC | Jul 18, 10:05 UTC | 1h 5m |
| 2026-07-05 | HBLKR | - | Jul 5, 03:30 UTC | Jul 5, 05:35 UTC | 2h 5m |
| 2026-07-02 | HBLKR | - | Jul 2, 08:50 UTC | Jul 2, 09:15 UTC | 25m |
| 2026-07-02 | HBLKR | - | Jul 2, 06:35 UTC | Jul 2, 08:10 UTC | 1h 35m |
| 2026-06-29 | HBLKR | - | Jun 29, 10:50 UTC | Jun 29, 12:00 UTC | 1h 10m |
| 2026-06-29 | HBLKR | - | Jun 29, 06:24 UTC | Jun 29, 07:34 UTC | 1h 10m |
| 2026-06-25 | HBLKR | - | Jun 25, 14:59 UTC | Jun 25, 15:15 UTC | 15m |
| 2026-06-25 | HBLKR | - | Jun 25, 12:19 UTC | Jun 25, 14:50 UTC | 2h 30m |
| 2026-06-24 | HBLKR | - | Jun 24, 10:45 UTC | Jun 24, 12:40 UTC | 1h 55m |
| 2026-06-23 | HBLKR | - | Jun 23, 15:34 UTC | Jun 23, 16:35 UTC | 1h 0m |
| 2026-06-23 | HBLKR | - | Jun 23, 08:04 UTC | Jun 23, 09:09 UTC | 1h 5m |
| 2026-06-22 | HBLKR | - | Jun 22, 08:15 UTC | Jun 22, 09:19 UTC | 1h 5m |
| 2026-06-16 | HBLKR | - | Jun 16, 17:49 UTC | Jun 16, 18:29 UTC | 40m |
| 2026-06-15 | HBLKR | - | Jun 15, 06:20 UTC | Jun 15, 07:00 UTC | 40m |
| 2026-06-11 | HBLKR | - | Jun 11, 13:50 UTC | Jun 11, 15:05 UTC | 1h 15m |
| 2026-06-11 | HBLKR | - | Jun 11, 06:25 UTC | Jun 11, 07:35 UTC | 1h 10m |
| 2026-06-10 | HBLKR | - | Jun 10, 11:50 UTC | Jun 10, 12:50 UTC | 1h 0m |
| 2026-06-10 | HBLKR | - | Jun 10, 08:15 UTC | Jun 10, 09:30 UTC | 1h 15m |
| 2026-06-05 | HBLKR | - | Jun 5, 07:15 UTC | Jun 5, 10:40 UTC | 3h 25m |
| 2026-05-23 | HBLKR | - | May 23, 18:35 UTC | May 23, 19:40 UTC | 1h 5m |
| 2026-05-21 | HBLKR | - | May 21, 12:10 UTC | May 21, 13:20 UTC | 1h 10m |
| 2026-05-07 | HBLKR | GAT → CEQ | May 7, 14:25 UTC | May 7, 14:55 UTC | 30m |
| 2026-05-07 | HBLKR | - | May 7, 07:05 UTC | May 7, 07:40 UTC | 35m |
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.