Apparatus

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sensors Mode-S transponder

A523C4

ICAO 24-bit transponder address · allocated to United States

Hex
A523C4
Octal
51221704
Decimal
10,822,596
Country
US
No current signal · last broadcast 3h ago
Flights observed
341
Distinct callsigns
1
Country
US
Last broadcast
3h ago

Last known position

Most recent position reported by Mode-S A523C4.

Country allocation

The ICAO 24-bit address A523C4 falls within the block assigned to United States (US) by ICAO Annex 10, Volume III. Every aircraft registered in United States 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
REH05 - 341 2026-07-20

Recent flights last 50

DateFlightRouteTakeoffLandingDuration
2026-07-20 REH05 - Jul 20, 21:05 UTCJul 20, 21:20 UTC15m
2026-07-20 REH05 - Jul 20, 10:20 UTCJul 20, 11:15 UTC55m
2026-07-20 REH05 - Jul 20, 08:05 UTCJul 20, 09:35 UTC1h 30m
2026-07-20 REH05 - Jul 20, 04:15 UTCJul 20, 05:55 UTC1h 40m
2026-07-20 REH05 - Jul 20, 03:15 UTCJul 20, 04:00 UTC45m
2026-07-20 REH05 - Jul 20, 01:50 UTCJul 20, 02:15 UTC25m
2026-07-19 REH05 - Jul 19, 22:15 UTCJul 19, 22:25 UTC10m
2026-07-19 REH05 - Jul 19, 20:55 UTCJul 19, 21:15 UTC20m
2026-07-19 REH05 - Jul 19, 14:45 UTCJul 19, 15:45 UTC1h 0m
2026-07-19 REH05 - Jul 19, 11:30 UTCJul 19, 12:35 UTC1h 5m
2026-07-18 REH05 - Jul 18, 21:30 UTCJul 18, 22:05 UTC35m
2026-07-18 REH05 - Jul 18, 19:45 UTCJul 18, 21:15 UTC1h 30m
2026-07-18 REH05 - Jul 18, 10:50 UTCJul 18, 11:45 UTC55m
2026-07-18 REH05 - Jul 18, 08:20 UTCJul 18, 09:55 UTC1h 35m
2026-07-18 REH05 - Jul 18, 06:45 UTCJul 18, 07:20 UTC35m
2026-07-18 REH05 - Jul 18, 05:30 UTCJul 18, 05:45 UTC15m
2026-07-18 REH05 - Jul 18, 03:35 UTCJul 18, 04:00 UTC25m
2026-07-17 REH05 - Jul 17, 09:20 UTCJul 17, 10:15 UTC55m
2026-07-17 REH05 - Jul 17, 07:50 UTCJul 17, 07:55 UTC5m
2026-07-17 REH05 - Jul 17, 05:45 UTCJul 17, 06:50 UTC1h 5m
2026-07-16 REH05 - Jul 16, 10:04 UTCJul 16, 11:40 UTC1h 35m
2026-07-16 REH05 - Jul 16, 06:50 UTCJul 16, 07:55 UTC1h 5m
2026-07-16 REH05 - Jul 16, 05:25 UTCJul 16, 05:45 UTC20m
2026-07-15 REH05 - Jul 15, 05:15 UTCJul 15, 05:30 UTC15m
2026-07-15 REH05 - Jul 15, 03:45 UTCJul 15, 04:15 UTC30m
2026-07-15 REH05 - Jul 15, 02:50 UTCJul 15, 03:05 UTC15m
2026-07-14 REH05 - Jul 14, 21:55 UTCJul 14, 22:10 UTC15m
2026-07-14 REH05 - Jul 14, 21:10 UTCJul 14, 21:20 UTC10m
2026-07-14 REH05 - Jul 14, 19:00 UTCJul 14, 19:10 UTC10m
2026-07-14 REH05 - Jul 14, 17:30 UTCJul 14, 17:50 UTC20m
2026-07-14 REH05 - Jul 14, 11:15 UTCJul 14, 11:55 UTC40m
2026-07-14 REH05 - Jul 14, 10:35 UTCJul 14, 11:00 UTC25m
2026-07-14 REH05 - Jul 14, 08:40 UTCJul 14, 09:05 UTC25m
2026-07-14 REH05 - Jul 14, 01:00 UTCJul 14, 01:10 UTC10m
2026-07-13 REH05 - Jul 13, 23:55 UTCJul 14, 00:05 UTC10m
2026-07-13 REH05 - Jul 13, 21:55 UTCJul 13, 22:10 UTC15m
2026-07-13 REH05 - Jul 13, 03:40 UTCJul 13, 05:25 UTC1h 45m
2026-07-13 REH05 - Jul 13, 03:01 UTCJul 13, 03:10 UTC10m
2026-07-13 REH05 - Jul 13, 00:25 UTCJul 13, 00:45 UTC20m
2026-07-12 REH05 - Jul 12, 22:05 UTCJul 12, 22:15 UTC10m
2026-07-12 REH05 - Jul 12, 09:15 UTCJul 12, 10:10 UTC55m
2026-07-12 REH05 - Jul 12, 07:15 UTCJul 12, 07:45 UTC30m
2026-07-12 REH05 - Jul 12, 05:45 UTCJul 12, 06:15 UTC30m
2026-07-12 REH05 - Jul 12, 03:01 UTCJul 12, 03:55 UTC55m
2026-07-12 REH05 - Jul 12, 00:40 UTCJul 12, 01:30 UTC50m
2026-07-11 REH05 - Jul 11, 23:50 UTCJul 12, 00:01 UTC10m
2026-07-11 REH05 - Jul 11, 00:10 UTCJul 11, 00:25 UTC15m
2026-07-10 REH05 - Jul 10, 22:45 UTCJul 10, 23:05 UTC20m
2026-07-10 REH05 - Jul 10, 16:00 UTCJul 10, 17:20 UTC1h 20m
2026-07-10 REH05 - Jul 10, 09:35 UTCJul 10, 09:45 UTC10m

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 A523C4 frequently asked

What is Mode-S code A523C4?
A523C4 is an ICAO 24-bit transponder address. Allocated to United States.
Where is Mode-S A523C4 registered?
Mode-S code A523C4 is allocated to United States (US). All aircraft registered there receive a Mode-S address from a fixed block defined by ICAO Annex 10.
Is A523C4 broadcasting right now?
No active broadcast right now. Last signal was 3h ago.
Hex, octal, and decimal Mode-S codes: what's the difference?
The same 24-bit identifier expressed in different bases: hex A523C4, octal 51221704, decimal 10,822,596.
What flights does A523C4 operate?
Mode-S A523C4 has broadcast 1 distinct callsign, including REH05.