Apparatus

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sensors Mode-S transponder

A1B8D1

ICAO 24-bit transponder address · allocated to United States

Currently assigned to N21SZ · CESSNA 172R Cutlass RG · operated by VISTA AIR INC

Hex
A1B8D1
Octal
50334321
Decimal
10,598,609
Country
US
Tail
N21SZ
Type
C72R
No current signal · last broadcast 8h ago
Flights observed
137
Distinct callsigns
1
Country
US
Last broadcast
8h ago

Last known position

Most recent position reported by Mode-S A1B8D1.

Country allocation

The ICAO 24-bit address A1B8D1 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
N21SZ - 137 2026-06-02

Recent flights last 50

DateFlightRouteTakeoffLandingDuration
2026-06-02 N21SZ WHP → WHP Jun 2, 21:30 UTCJun 2, 21:35 UTC5m
2026-06-02 N21SZ WHP → WHP Jun 2, 19:55 UTCJun 2, 20:05 UTC10m
2026-06-02 N21SZ - Jun 2, 19:15 UTCJun 2, 19:35 UTC20m
2026-06-02 N21SZ - Jun 2, 18:50 UTCJun 2, 18:55 UTC5m
2026-06-02 N21SZ WHP → WHP Jun 2, 01:30 UTCJun 2, 01:45 UTC15m
2026-06-02 N21SZ WHP → WHP Jun 2, 00:55 UTCJun 2, 01:05 UTC10m
2026-06-01 N21SZ WHP → WHP Jun 1, 21:55 UTCJun 1, 23:05 UTC1h 10m
2026-06-01 N21SZ WHP → WHP Jun 1, 00:10 UTCJun 1, 00:45 UTC35m
2026-05-31 N21SZ - May 31, 23:10 UTCMay 31, 23:20 UTC10m
2026-05-31 N21SZ WHP → WHP May 31, 22:15 UTCMay 31, 23:05 UTC50m
2026-05-31 N21SZ - May 31, 20:05 UTCMay 31, 20:55 UTC50m
2026-05-31 N21SZ - May 31, 18:05 UTCMay 31, 19:30 UTC1h 25m
2026-05-31 N21SZ BFL → WHP May 31, 15:25 UTCMay 31, 16:50 UTC1h 25m
2026-05-31 N21SZ WHP → BFL May 31, 14:30 UTCMay 31, 15:20 UTC50m
2026-05-30 N21SZ BFL → WHP May 30, 21:00 UTCMay 30, 21:50 UTC50m
2026-05-30 N21SZ WHP → BFL May 30, 19:55 UTCMay 30, 20:50 UTC55m
2026-05-29 N21SZ WHP → WHP May 29, 20:30 UTCMay 29, 21:00 UTC30m
2026-05-28 N21SZ - May 28, 21:20 UTCMay 28, 22:45 UTC1h 25m
2026-05-28 N21SZ - May 28, 19:55 UTCMay 28, 20:00 UTC5m
2026-05-28 N21SZ - May 28, 19:40 UTCMay 28, 19:50 UTC10m
2026-05-28 N21SZ - May 28, 19:05 UTCMay 28, 19:25 UTC20m
2026-05-28 N21SZ WHP → WHP May 28, 18:55 UTCMay 28, 19:00 UTC5m
2026-05-27 N21SZ WHP → WHP May 27, 01:44 UTCMay 27, 02:24 UTC40m
2026-05-26 N21SZ WHP → WHP May 26, 00:35 UTCMay 26, 01:40 UTC1h 5m
2026-05-25 N21SZ - May 25, 20:45 UTCMay 25, 21:19 UTC35m
2026-05-25 N21SZ WHP → WHP May 25, 17:30 UTCMay 25, 17:35 UTC5m
2026-05-25 N21SZ - May 25, 16:25 UTCMay 25, 17:20 UTC55m
2026-05-24 N21SZ - May 24, 23:00 UTCMay 24, 23:20 UTC20m
2026-05-24 N21SZ - May 24, 20:20 UTCMay 24, 21:10 UTC50m
2026-05-24 N21SZ - May 24, 19:30 UTCMay 24, 19:45 UTC15m
2026-05-24 N21SZ - May 24, 00:00 UTCMay 24, 00:40 UTC40m
2026-05-23 N21SZ - May 23, 19:05 UTCMay 23, 19:15 UTC10m
2026-05-23 N21SZ - May 23, 18:35 UTCMay 23, 18:45 UTC10m
2026-05-23 N21SZ WHP → WHP May 23, 18:05 UTCMay 23, 18:15 UTC11m
2026-05-23 N21SZ WHP → WHP May 23, 00:15 UTCMay 23, 00:20 UTC5m
2026-05-22 N21SZ - May 22, 00:55 UTCMay 22, 01:35 UTC40m
2026-05-21 N21SZ - May 21, 22:45 UTCMay 22, 00:00 UTC1h 15m
2026-05-21 N21SZ - May 21, 13:50 UTCMay 21, 16:01 UTC2h 10m
2026-05-20 N21SZ WHP → WHP May 20, 19:45 UTCMay 20, 20:15 UTC30m
2026-05-20 N21SZ - May 20, 19:20 UTCMay 20, 19:35 UTC15m
2026-05-20 N21SZ WHP → WHP May 20, 18:50 UTCMay 20, 18:55 UTC5m
2026-05-19 N21SZ - May 19, 23:10 UTCMay 19, 23:40 UTC30m
2026-05-19 N21SZ - May 19, 22:00 UTCMay 19, 22:25 UTC25m
2026-05-19 N21SZ - May 19, 19:50 UTCMay 19, 20:00 UTC10m
2026-05-19 N21SZ - May 19, 19:25 UTCMay 19, 19:35 UTC10m
2026-05-19 N21SZ WHP → WHP May 19, 15:20 UTCMay 19, 16:15 UTC55m
2026-05-18 N21SZ WHP → WHP May 18, 16:55 UTCMay 18, 17:10 UTC15m
2026-05-18 N21SZ - May 18, 00:40 UTCMay 18, 00:50 UTC10m
2026-05-17 N21SZ - May 17, 23:55 UTCMay 18, 00:00 UTC5m
2026-05-16 N21SZ WHP → WHP May 16, 21:20 UTCMay 16, 21:45 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.

Prefer a tail-number view? See the N21SZ page for operator, model, and routing details .

Mode-S A1B8D1 frequently asked

What is Mode-S code A1B8D1?
A1B8D1 is an ICAO 24-bit transponder address. Allocated to United States. Assigned to N21SZ.
Where is Mode-S A1B8D1 registered?
Mode-S code A1B8D1 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 A1B8D1 broadcasting right now?
No active broadcast right now. Last signal was 8h ago.
Hex, octal, and decimal Mode-S codes: what's the difference?
The same 24-bit identifier expressed in different bases: hex A1B8D1, octal 50334321, decimal 10,598,609.
What flights does A1B8D1 operate?
Mode-S A1B8D1 has broadcast 1 distinct callsign, including N21SZ.