sensors Mode-S transponder
781621
ICAO 24-bit transponder address · allocated to China
Currently assigned to B-306K · AIRBUS A-321neo
- Hex
- 781621
- Octal
- 36013041
- Decimal
- 7,869,985
- Country
- CN
- Tail
- B-306K
- Type
- A21N
- Flights observed
- 4
- Distinct callsigns
- 3
- Country
- CN
- Last broadcast
- 13h ago
Last known position
Country allocation
The ICAO 24-bit address 781621 falls within the block assigned to China (CN) by ICAO Annex 10, Volume III. Every aircraft registered in China 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 3 distinct
| Callsign | Airline | Flights | Last seen |
|---|---|---|---|
| CSN6405 | China Southern Airlines | 2 | 2026-04-18 |
| CSN624 | China Southern Airlines | 1 | 2026-04-16 |
| CSN623 | China Southern Airlines | 1 | 2026-04-16 |
Recent flights last 4
| Date | Flight | Route | Takeoff | Landing | Duration |
|---|---|---|---|---|---|
| 2026-04-18 | CSN6405 | CGQ → HGH | Apr 18, 08:55 UTC | Apr 19, 00:55 UTC | 16h 0m |
| 2026-04-18 | CSN6405 | CGQ → HGH | Apr 18, 01:05 UTC | Apr 18, 14:10 UTC | 13h 5m |
| 2026-04-16 | CSN624 | NRT → CGQ | Apr 16, 05:29 UTC | Apr 16, 06:05 UTC | 35m |
| 2026-04-16 | CSN623 | CGQ → NRT | Apr 16, 01:35 UTC | Apr 16, 02:24 UTC | 50m |
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 B-306K page for operator, model, and routing details .