Apparatus

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sensors Mode-S transponder

4521BF

ICAO 24-bit transponder address · allocated to Bulgaria

Hex
4521BF
Octal
21220677
Decimal
4,530,623
Country
BG
No current signal · last broadcast 1h ago
Flights observed
148
Distinct callsigns
20
Country
BG
Last broadcast
1h ago

Last known position

Most recent position reported by Mode-S 4521BF.

Country allocation

The ICAO 24-bit address 4521BF falls within the block assigned to Bulgaria (BG) by ICAO Annex 10, Volume III. Every aircraft registered in Bulgaria 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
GPX6UC - 24 2026-06-29
GPX6CU GP Aviation 24 2026-06-29
GPX5AS GP Aviation 8 2026-06-30
GPX5SA - 7 2026-06-30
BBG272 - 7 2026-07-10
BBG271 - 6 2026-07-10
GPX5ZP - 5 2026-06-24
GPX5PZ - 5 2026-06-24
GPX9RE - 4 2026-06-28
GPX9ER - 4 2026-06-28
GPX8WK - 4 2026-06-21
GPX8KW - 4 2026-06-21
GPX6YN - 3 2026-06-20
GPX6NY - 3 2026-06-20
LZLAN - 2 2026-05-16
GPX8TD - 2 2026-06-02
GPX8DT - 2 2026-06-02
GPX4VA - 2 2026-06-27
GPX4AV - 2 2026-06-27
CYF152 - 2 2026-07-03

Recent flights last 50

DateFlightRouteTakeoffLandingDuration
2026-07-12 CYF158 TLV → PFO Jul 12, 15:01 UTCJul 12, 15:40 UTC40m
2026-07-12 BBG561 - Jul 12, 11:15 UTCJul 12, 13:05 UTC1h 50m
2026-07-12 BBG562 - Jul 12, 07:15 UTCJul 12, 09:00 UTC1h 45m
2026-07-11 BBG261 MUC → TLV Jul 11, 16:10 UTCJul 11, 19:30 UTC3h 20m
2026-07-11 BBG262 - Jul 11, 11:20 UTCJul 11, 15:00 UTC3h 40m
2026-07-10 BBG271 - Jul 10, 18:40 UTCJul 10, 22:00 UTC3h 20m
2026-07-10 BBG272 TLV → BER Jul 10, 13:40 UTCJul 10, 17:35 UTC3h 55m
2026-07-10 BBG801 - Jul 10, 10:05 UTCJul 10, 11:25 UTC1h 20m
2026-07-10 BBG802 TLV → KGS Jul 10, 07:10 UTCJul 10, 08:25 UTC1h 15m
2026-07-09 BBG271 BER → TLV Jul 9, 19:35 UTCJul 9, 23:00 UTC3h 25m
2026-07-09 BBG272 TLV → BER Jul 9, 14:15 UTCJul 9, 18:20 UTC4h 5m
2026-07-09 BBG691 RHO → TLV Jul 9, 10:40 UTCJul 9, 11:50 UTC1h 10m
2026-07-09 BBG692 TLV → RHO Jul 9, 07:05 UTCJul 9, 08:15 UTC1h 10m
2026-07-08 CYF461 PRG → TLV Jul 8, 19:10 UTCJul 8, 22:25 UTC3h 15m
2026-07-08 CYF462 TLV → PRG Jul 8, 13:20 UTCJul 8, 17:05 UTC3h 45m
2026-07-08 CYF217 - Jul 8, 09:25 UTCJul 8, 11:20 UTC1h 55m
2026-07-08 CYF216 TLV → SKG Jul 8, 05:05 UTCJul 8, 07:15 UTC2h 10m
2026-07-07 BBG273 BER → TLV Jul 7, 17:40 UTCJul 7, 21:15 UTC3h 35m
2026-07-07 BBG272 TLV → BER Jul 7, 11:45 UTCJul 7, 15:45 UTC4h 0m
2026-07-07 BBG761 - Jul 7, 08:55 UTCJul 7, 10:20 UTC1h 25m
2026-07-07 BBG762 - Jul 7, 05:30 UTCJul 7, 07:05 UTC1h 35m
2026-07-06 BBG271 BER → TLV Jul 6, 17:05 UTCJul 6, 20:35 UTC3h 30m
2026-07-06 BBG272 TLV → BER Jul 6, 11:40 UTCJul 6, 15:30 UTC3h 50m
2026-07-06 BBG691 RHO → TLV Jul 6, 09:20 UTCJul 6, 10:30 UTC1h 10m
2026-07-06 BBG692 TLV → RHO Jul 6, 06:35 UTCJul 6, 07:50 UTC1h 15m
2026-07-05 BBG317 VIE → TLV Jul 5, 16:40 UTCJul 5, 19:35 UTC2h 55m
2026-07-05 BBG316 - Jul 5, 11:30 UTCJul 5, 14:50 UTC3h 20m
2026-07-04 BBG261 MUC → TLV Jul 4, 18:15 UTCJul 4, 21:20 UTC3h 5m
2026-07-04 BBG262 TLV → MUC Jul 4, 13:20 UTCJul 4, 17:05 UTC3h 45m
2026-07-04 BBG754 TLV → TLV Jul 4, 07:15 UTCJul 4, 11:40 UTC4h 25m
2026-07-03 BBG271 BER → TLV Jul 3, 17:05 UTCJul 3, 20:30 UTC3h 25m
2026-07-03 BBG272 TLV → BER Jul 3, 11:30 UTCJul 3, 15:40 UTC4h 10m
2026-07-03 CYF152 - Jul 3, 00:45 UTCJul 3, 01:30 UTC45m
2026-07-02 BBG271 BER → TLV Jul 2, 18:30 UTCJul 2, 22:05 UTC3h 35m
2026-07-02 BBG272 TLV → BER Jul 2, 13:25 UTCJul 2, 17:25 UTC4h 0m
2026-07-02 BBG801 KGS → TLV Jul 2, 09:50 UTCJul 2, 11:10 UTC1h 20m
2026-07-02 BBG802 TLV → KGS Jul 2, 06:15 UTCJul 2, 07:35 UTC1h 20m
2026-07-01 BBG271 BER → TLV Jul 1, 21:30 UTCJul 2, 01:15 UTC3h 45m
2026-07-01 BBG272 TLV → BER Jul 1, 15:50 UTCJul 1, 19:25 UTC3h 35m
2026-07-01 CYF153 - Jul 1, 06:10 UTCJul 1, 06:55 UTC45m
2026-07-01 CYF152 - Jul 1, 04:20 UTCJul 1, 05:05 UTC45m
2026-07-01 CYF898P - Jul 1, 00:50 UTCJul 1, 03:00 UTC2h 10m
2026-06-30 GPX5AS STR → STR Jun 30, 12:50 UTCJun 30, 14:20 UTC1h 30m
2026-06-30 GPX5SA - Jun 30, 09:50 UTCJun 30, 11:20 UTC1h 30m
2026-06-29 GPX6CU MUC → MUC Jun 29, 12:55 UTCJun 29, 14:25 UTC1h 30m
2026-06-29 GPX6UC - Jun 29, 10:10 UTCJun 29, 11:29 UTC1h 20m
2026-06-28 GPX9RE - Jun 28, 19:59 UTCJun 28, 21:59 UTC2h 0m
2026-06-28 GPX9ER - Jun 28, 16:35 UTCJun 28, 18:29 UTC1h 55m
2026-06-28 GPX6CU MUC → MUC Jun 28, 12:55 UTCJun 28, 14:04 UTC1h 10m
2026-06-28 GPX6UC - Jun 28, 10:10 UTCJun 28, 11:29 UTC1h 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.

Mode-S 4521BF frequently asked

What is Mode-S code 4521BF?
4521BF is an ICAO 24-bit transponder address. Allocated to Bulgaria.
Where is Mode-S 4521BF registered?
Mode-S code 4521BF is allocated to Bulgaria (BG). All aircraft registered there receive a Mode-S address from a fixed block defined by ICAO Annex 10.
Is 4521BF broadcasting right now?
No active broadcast right now. Last signal was 1h ago.
Hex, octal, and decimal Mode-S codes: what's the difference?
The same 24-bit identifier expressed in different bases: hex 4521BF, octal 21220677, decimal 4,530,623.
What flights does 4521BF operate?
Mode-S 4521BF has broadcast 20 distinct callsigns, including GPX6UC, GPX6CU, GPX5AS, GPX5SA, BBG272.