Apparatus

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sensors Mode-S transponder

4521CF

ICAO 24-bit transponder address · allocated to Bulgaria

Hex
4521CF
Octal
21220717
Decimal
4,530,639
Country
BG
No current signal · last broadcast Jul 26, 15:50 UTC
Flights observed
152
Distinct callsigns
20
Country
BG
Last broadcast
Jul 26, 15:50 UTC

Last known position

Most recent position reported by Mode-S 4521CF.

Country allocation

The ICAO 24-bit address 4521CF 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
AEZ2617 Aerial Transit Company 6 2026-07-23
AEZ7810 - 5 2026-07-01
AEZ70MH Aerial Transit Company 5 2026-05-11
AEZ49KF Aerial Transit Company 5 2026-06-20
AEZ44LG - 5 2026-07-05
AEZ88LL Aerial Transit Company 4 2026-06-15
AEZ569P Aerial Transit Company 4 2026-07-23
AEZ2347 Aerial Transit Company 4 2026-06-07
AEZ155Z - 4 2026-06-24
AEZ139V - 4 2026-06-19
AEZ7816 Aerial Transit Company 3 2026-07-23
AEZ7117 - 3 2026-06-16
AEZ385Z Aerial Transit Company 3 2026-07-25
AEZ318W Aerial Transit Company 3 2026-05-18
AEZ29JD Aerial Transit Company 3 2026-07-26
AEZ2825 Aerial Transit Company 3 2026-07-19
AEZ2824 Aerial Transit Company 3 2026-07-19
AEZ2367 Aerial Transit Company 3 2026-05-25
AEZ2363 Aerial Transit Company 3 2026-06-15
AEZ2349 Aerial Transit Company 3 2026-05-01

Recent flights last 50

DateFlightRouteTakeoffLandingDuration
2026-07-26 AEZ29JD OLB → LIN Jul 26, 14:55 UTCJul 26, 15:45 UTC50m
2026-07-25 AEZ385Z OLB → LIN Jul 25, 17:25 UTCJul 25, 18:05 UTC40m
2026-07-24 AEZ7341 LIN → OLB Jul 24, 20:45 UTCJul 24, 21:40 UTC55m
2026-07-24 AEZ7340 OLB → LIN Jul 24, 18:40 UTCJul 24, 19:30 UTC50m
2026-07-24 AEZ29JD OLB → LIN Jul 24, 14:45 UTCJul 24, 15:35 UTC50m
2026-07-23 AEZ2617 FCO → OLB Jul 23, 19:45 UTCJul 23, 20:05 UTC20m
2026-07-23 AEZ7816 OLB → FCO Jul 23, 17:55 UTCJul 23, 18:25 UTC30m
2026-07-23 AEZ569P FCO → OLB Jul 23, 16:15 UTCJul 23, 16:50 UTC35m
2026-07-22 AEZ157Q FCO → CTA Jul 22, 19:55 UTCJul 22, 20:40 UTC45m
2026-07-22 AEZ11GR CAG → FCO Jul 22, 11:30 UTCJul 22, 12:00 UTC30m
2026-07-22 AEZ100N FCO → CAG Jul 22, 05:05 UTCJul 22, 05:25 UTC20m
2026-07-19 AEZ2824 BGY → CTA Jul 19, 14:45 UTCJul 19, 16:00 UTC1h 15m
2026-07-19 AEZ2825 CTA → BGY Jul 19, 12:05 UTCJul 19, 13:30 UTC1h 25m
2026-07-17 AEZ2824 BGY → CTA Jul 17, 15:10 UTCJul 17, 16:29 UTC1h 20m
2026-07-17 AEZ2825 CTA → BGY Jul 17, 12:00 UTCJul 17, 13:29 UTC1h 30m
2026-07-17 AEZ158C - Jul 17, 10:00 UTCJul 17, 10:44 UTC45m
2026-07-17 AEZ40GR - Jul 17, 07:20 UTCJul 17, 08:04 UTC45m
2026-07-15 AEZ14UJ - Jul 15, 15:25 UTCJul 15, 16:25 UTC1h 0m
2026-07-11 AEZ385Z OLB → LIN Jul 11, 19:25 UTCJul 11, 20:10 UTC45m
2026-07-06 AEZ14UJ - Jul 6, 15:10 UTCJul 6, 16:05 UTC55m
2026-07-06 AEZ47LG - Jul 6, 10:40 UTCJul 6, 11:35 UTC55m
2026-07-06 AEZ8094 - Jul 6, 08:20 UTCJul 6, 09:20 UTC1h 0m
2026-07-05 AEZ14UJ - Jul 5, 15:45 UTCJul 5, 16:45 UTC1h 0m
2026-07-05 AEZ47LG - Jul 5, 11:00 UTCJul 5, 12:10 UTC1h 10m
2026-07-05 AEZ44LG - Jul 5, 06:30 UTCJul 5, 07:25 UTC55m
2026-07-04 AEZ112X - Jul 4, 11:15 UTCJul 4, 11:40 UTC25m
2026-07-04 AEZ2330 - Jul 4, 04:20 UTCJul 4, 05:00 UTC40m
2026-07-03 AEZ8041 - Jul 3, 06:20 UTCJul 3, 07:15 UTC55m
2026-07-01 AEZ7810 - Jul 1, 05:15 UTCJul 1, 05:50 UTC35m
2026-06-30 AEZ7810 OLB → FCO Jun 30, 05:20 UTCJun 30, 05:45 UTC25m
2026-06-30 AEZ2617 - Jun 30, 00:09 UTCJun 30, 00:35 UTC25m
2026-06-29 AEZ7816 OLB → FCO Jun 29, 22:44 UTCJun 29, 23:09 UTC25m
2026-06-29 AEZ833J LIN → OLB Jun 29, 20:30 UTCJun 29, 21:24 UTC55m
2026-06-28 AEZ2617 - Jun 28, 20:25 UTCJun 28, 20:59 UTC35m
2026-06-28 AEZ7816 OLB → FCO Jun 28, 18:14 UTCJun 28, 18:49 UTC35m
2026-06-28 AEZ7811 FCO → OLB Jun 28, 05:49 UTCJun 28, 06:24 UTC35m
2026-06-27 AEZ7811 FCO → OLB Jun 27, 05:55 UTCJun 27, 06:19 UTC25m
2026-06-24 AEZ155Z - Jun 24, 08:04 UTCJun 24, 08:49 UTC45m
2026-06-24 AEZ516C - Jun 24, 05:05 UTCJun 24, 06:04 UTC1h 0m
2026-06-23 AEZ7817 FCO → OLB Jun 23, 19:10 UTCJun 23, 19:39 UTC30m
2026-06-23 AEZ418P - Jun 23, 17:39 UTCJun 23, 18:10 UTC30m
2026-06-23 AEZ11GR - Jun 23, 11:19 UTCJun 23, 11:59 UTC40m
2026-06-23 AEZ100N FCO → CAG Jun 23, 05:24 UTCJun 23, 06:04 UTC40m
2026-06-22 AEZ2575 - Jun 22, 20:44 UTCJun 22, 22:10 UTC1h 25m
2026-06-22 AEZ2575 IBZ → IBZ Jun 22, 16:34 UTCJun 22, 17:00 UTC25m
2026-06-22 AEZ2574 - Jun 22, 13:29 UTCJun 22, 15:05 UTC1h 35m
2026-06-22 AEZ419P - Jun 22, 05:54 UTCJun 22, 06:10 UTC15m
2026-06-20 AEZ49KF CAG → LIN Jun 20, 18:34 UTCJun 20, 19:29 UTC55m
2026-06-20 AEZ11LJ FCO → CAG Jun 20, 16:29 UTCJun 20, 16:59 UTC30m
2026-06-20 AEZ131R FCO → OLB Jun 20, 11:54 UTCJun 20, 12:19 UTC25m

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 4521CF frequently asked

What is Mode-S code 4521CF?
4521CF is an ICAO 24-bit transponder address. Allocated to Bulgaria.
Where is Mode-S 4521CF registered?
Mode-S code 4521CF is allocated to Bulgaria (BG). All aircraft registered there receive a Mode-S address from a fixed block defined by ICAO Annex 10.
Is 4521CF broadcasting right now?
No active broadcast right now. Last signal was Jul 26, 15:50 UTC.
Hex, octal, and decimal Mode-S codes: what's the difference?
The same 24-bit identifier expressed in different bases: hex 4521CF, octal 21220717, decimal 4,530,639.
What flights does 4521CF operate?
Mode-S 4521CF has broadcast 20 distinct callsigns, including AEZ2617, AEZ7810, AEZ70MH, AEZ49KF, AEZ44LG.