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
Broadcasting now · callsign BBG154 · 36,000 ft
Flights observed
198
Distinct callsigns
20
Country
BG
Last broadcast
Jul 26, 21:35 UTC

Current position

4521BF is currently broadcasting. Map zoomed to live position.

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
BBG562 Bluebird Airways (BZ) 8 2026-07-26
BBG561 - 8 2026-07-26
BBG272 Bluebird Airways (BZ) 8 2026-07-23
GPX5SA - 7 2026-06-30
BBG271 Bluebird Airways (BZ) 7 2026-07-23
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
CYF462 Company Flight 3 2026-07-24
CYF461 Company Flight 3 2026-07-24
BBG442 Bluebird Airways (BZ) 3 2026-07-26
BBG441 Bluebird Airways (BZ) 3 2026-07-26

Recent flights last 50

DateFlightRouteTakeoffLandingDuration
2026-07-26 BBG441 BUD → TLV Jul 26, 18:45 UTCJul 26, 21:25 UTC2h 40m
2026-07-26 BBG442 TLV → BUD Jul 26, 14:05 UTCJul 26, 17:10 UTC3h 5m
2026-07-26 BBG561 - Jul 26, 10:15 UTCJul 26, 12:00 UTC1h 45m
2026-07-26 BBG562 TLV → BOJ Jul 26, 06:50 UTCJul 26, 08:40 UTC1h 50m
2026-07-25 BBG441 BUD → TLV Jul 25, 17:25 UTCJul 25, 20:05 UTC2h 40m
2026-07-25 BBG442 TLV → BUD Jul 25, 12:45 UTCJul 25, 15:45 UTC3h 0m
2026-07-25 BBG561 - Jul 25, 09:20 UTCJul 25, 11:10 UTC1h 50m
2026-07-25 BBG562 TLV → BOJ Jul 25, 06:15 UTCJul 25, 08:05 UTC1h 50m
2026-07-24 CYF461 PRG → TLV Jul 24, 17:25 UTCJul 24, 20:40 UTC3h 15m
2026-07-24 CYF462 TLV → PRG Jul 24, 10:00 UTCJul 24, 13:35 UTC3h 35m
2026-07-23 BBG271 BER → TLV Jul 23, 18:00 UTCJul 23, 21:35 UTC3h 35m
2026-07-23 BBG272 TLV → BER Jul 23, 12:55 UTCJul 23, 16:55 UTC4h 0m
2026-07-23 BBG561 - Jul 23, 09:40 UTCJul 23, 11:30 UTC1h 50m
2026-07-23 BBG562 TLV → BOJ Jul 23, 06:10 UTCJul 23, 08:10 UTC2h 0m
2026-07-22 BBG703 ATH → TLV Jul 22, 18:55 UTCJul 22, 20:40 UTC1h 45m
2026-07-22 BBG704 TLV → ATH Jul 22, 15:30 UTCJul 22, 17:20 UTC1h 50m
2026-07-21 BBG755 HER → TLV Jul 21, 21:40 UTCJul 21, 22:45 UTC1h 5m
2026-07-21 BBG758 TLV → HER Jul 21, 18:30 UTCJul 21, 19:35 UTC1h 5m
2026-07-21 BBG561 - Jul 21, 14:20 UTCJul 21, 16:10 UTC1h 50m
2026-07-21 BBG562 TLV → BOJ Jul 21, 09:25 UTCJul 21, 11:20 UTC1h 55m
2026-07-20 CYF102 LCA → TLV Jul 20, 18:45 UTCJul 20, 19:20 UTC35m
2026-07-20 CYF107 TLV → LCA Jul 20, 16:45 UTCJul 20, 17:25 UTC40m
2026-07-20 BBG741 HER → TLV Jul 20, 11:05 UTCJul 20, 15:25 UTC4h 20m
2026-07-20 CYF108 LCA → TLV Jul 20, 09:00 UTCJul 20, 09:40 UTC40m
2026-07-20 CYF103 - Jul 20, 07:00 UTCJul 20, 07:40 UTC40m
2026-07-19 BBG317 VIE → TLV Jul 19, 15:25 UTCJul 19, 18:25 UTC3h 0m
2026-07-19 BBG316 TLV → VIE Jul 19, 07:55 UTCJul 19, 11:10 UTC3h 15m
2026-07-18 BBG441 BUD → TLV Jul 18, 17:20 UTCJul 18, 20:05 UTC2h 45m
2026-07-18 BBG442 TLV → BUD Jul 18, 12:50 UTCJul 18, 15:50 UTC3h 0m
2026-07-18 BBG561 - Jul 18, 09:15 UTCJul 18, 11:00 UTC1h 45m
2026-07-18 BBG562 - Jul 18, 06:15 UTCJul 18, 08:10 UTC1h 55m
2026-07-17 CYF461 PRG → TLV Jul 17, 17:55 UTCJul 17, 21:15 UTC3h 20m
2026-07-17 CYF462 TLV → PRG Jul 17, 13:05 UTCJul 17, 16:44 UTC3h 40m
2026-07-17 BBG561 - Jul 17, 10:00 UTCJul 17, 11:45 UTC1h 45m
2026-07-17 BBG562 - Jul 17, 06:40 UTCJul 17, 08:45 UTC2h 5m
2026-07-16 CYF159 - Jul 16, 15:10 UTCJul 16, 16:00 UTC50m
2026-07-16 CYF158 TLV → PFO Jul 16, 13:20 UTCJul 16, 14:00 UTC40m
2026-07-16 BBG561 - Jul 16, 09:55 UTCJul 16, 11:45 UTC1h 50m
2026-07-16 BBG562 - Jul 16, 05:50 UTCJul 16, 07:45 UTC1h 55m
2026-07-15 CYF235 - Jul 15, 17:25 UTCJul 15, 19:30 UTC2h 5m
2026-07-15 CYF234 - Jul 15, 13:45 UTCJul 15, 15:50 UTC2h 5m
2026-07-15 BBG747 - Jul 15, 09:35 UTCJul 15, 10:45 UTC1h 10m
2026-07-15 BBG746 - Jul 15, 06:35 UTCJul 15, 07:40 UTC1h 5m
2026-07-14 BBG317 VIE → TLV Jul 14, 16:45 UTCJul 14, 19:40 UTC2h 55m
2026-07-14 BBG316 TLV → VIE Jul 14, 11:55 UTCJul 14, 15:20 UTC3h 25m
2026-07-13 BBG155 - Jul 13, 17:15 UTCJul 13, 20:35 UTC3h 20m
2026-07-13 BBG154 - Jul 13, 12:30 UTCJul 13, 16:05 UTC3h 35m
2026-07-13 CYF108 - Jul 13, 07:25 UTCJul 13, 08:01 UTC35m
2026-07-13 CYF103 - Jul 13, 05:35 UTCJul 13, 06:15 UTC40m
2026-07-12 CYF159 - Jul 12, 16:55 UTCJul 12, 17:45 UTC50m

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?
Yes. Mode-S 4521BF is currently airborne.
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, BBG562, BBG561.