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sensors Mode-S transponder

A21D90

ICAO 24-bit transponder address · allocated to United States

Currently assigned to N2351B · PIPER PA-28-140/150/160/180

Hex
A21D90
Octal
50416620
Decimal
10,624,400
Country
US
Tail
N2351B
Type
P28A
No current signal · last broadcast 19d ago
Flights observed
70
Distinct callsigns
1
Country
US
Last broadcast
19d ago

Last known position

Most recent position reported by Mode-S A21D90.

Country allocation

The ICAO 24-bit address A21D90 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
N2351B - 70 2026-07-16

Recent flights last 50

DateFlightRouteTakeoffLandingDuration
2026-07-16 N2351B - Jul 16, 16:30 UTCJul 16, 17:35 UTC1h 5m
2026-07-16 N2351B - Jul 16, 15:05 UTCJul 16, 15:35 UTC30m
2026-07-15 N2351B - Jul 15, 17:45 UTCJul 15, 18:00 UTC15m
2026-07-15 N2351B - Jul 15, 14:00 UTCJul 15, 14:40 UTC40m
2026-07-10 N2351B - Jul 10, 16:25 UTCJul 10, 17:00 UTC35m
2026-07-10 N2351B - Jul 10, 14:55 UTCJul 10, 15:30 UTC35m
2026-07-09 N2351B - Jul 9, 16:15 UTCJul 9, 16:50 UTC35m
2026-07-09 N2351B - Jul 9, 14:50 UTCJul 9, 15:20 UTC30m
2026-07-05 N2351B - Jul 5, 17:05 UTCJul 5, 17:20 UTC15m
2026-07-05 N2351B - Jul 5, 14:55 UTCJul 5, 15:25 UTC30m
2026-07-04 N2351B - Jul 4, 16:45 UTCJul 4, 17:15 UTC30m
2026-07-04 N2351B - Jul 4, 14:40 UTCJul 4, 15:15 UTC35m
2026-07-01 N2351B - Jul 1, 19:10 UTCJul 1, 19:20 UTC10m
2026-07-01 N2351B - Jul 1, 15:35 UTCJul 1, 16:15 UTC40m
2026-06-30 N2351B - Jun 30, 17:50 UTCJun 30, 18:15 UTC25m
2026-06-30 N2351B - Jun 30, 16:50 UTCJun 30, 17:10 UTC20m
2026-06-30 N2351B - Jun 30, 15:10 UTCJun 30, 15:50 UTC40m
2026-06-26 N2351B - Jun 26, 17:04 UTCJun 26, 18:15 UTC1h 10m
2026-06-26 N2351B - Jun 26, 15:20 UTCJun 26, 15:45 UTC25m
2026-06-24 N2351B - Jun 24, 18:50 UTCJun 24, 19:10 UTC20m
2026-06-24 N2351B - Jun 24, 13:00 UTCJun 24, 13:30 UTC30m
2026-06-21 N2351B - Jun 21, 19:05 UTCJun 21, 19:24 UTC20m
2026-06-21 N2351B - Jun 21, 15:15 UTCJun 21, 15:49 UTC35m
2026-06-20 N2351B - Jun 20, 17:10 UTCJun 20, 17:49 UTC40m
2026-06-20 N2351B - Jun 20, 14:59 UTCJun 20, 15:34 UTC35m
2026-06-17 N2351B - Jun 17, 18:25 UTCJun 17, 18:35 UTC10m
2026-06-17 N2351B - Jun 17, 15:05 UTCJun 17, 15:30 UTC25m
2026-06-13 N2351B - Jun 13, 17:00 UTCJun 13, 17:25 UTC25m
2026-06-13 N2351B - Jun 13, 15:00 UTCJun 13, 15:15 UTC15m
2026-06-11 N2351B - Jun 11, 16:25 UTCJun 11, 17:05 UTC40m
2026-06-11 N2351B - Jun 11, 14:45 UTCJun 11, 15:20 UTC35m
2026-06-07 N2351B - Jun 7, 19:35 UTCJun 7, 19:50 UTC15m
2026-06-07 N2351B - Jun 7, 15:15 UTCJun 7, 15:45 UTC30m
2026-06-05 N2351B - Jun 5, 17:25 UTCJun 5, 18:00 UTC35m
2026-06-05 N2351B - Jun 5, 15:15 UTCJun 5, 15:50 UTC35m
2026-06-03 N2351B - Jun 3, 18:50 UTCJun 3, 19:25 UTC35m
2026-06-03 N2351B - Jun 3, 17:35 UTCJun 3, 18:05 UTC30m
2026-06-03 N2351B - Jun 3, 12:50 UTCJun 3, 13:15 UTC25m
2026-06-03 N2351B - Jun 3, 11:35 UTCJun 3, 12:15 UTC40m
2026-05-29 N2351B - May 29, 19:10 UTCMay 29, 19:20 UTC10m
2026-05-29 N2351B - May 29, 15:05 UTCMay 29, 15:25 UTC20m
2026-05-28 N2351B - May 28, 16:35 UTCMay 28, 17:15 UTC40m
2026-05-28 N2351B - May 28, 15:05 UTCMay 28, 15:35 UTC30m
2026-05-21 N2351B - May 21, 17:10 UTCMay 21, 17:35 UTC25m
2026-05-21 N2351B - May 21, 15:10 UTCMay 21, 15:45 UTC35m
2026-05-19 N2351B - May 19, 16:45 UTCMay 19, 16:55 UTC10m
2026-05-19 N2351B - May 19, 14:15 UTCMay 19, 14:25 UTC10m
2026-05-18 N2351B - May 18, 17:05 UTCMay 18, 17:35 UTC30m
2026-05-18 N2351B - May 18, 15:30 UTCMay 18, 16:00 UTC30m
2026-05-15 N2351B - May 15, 13:30 UTCMay 15, 13:45 UTC15m

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 N2351B page for operator, model, and routing details .

Mode-S A21D90 frequently asked

What is Mode-S code A21D90?
A21D90 is an ICAO 24-bit transponder address. Allocated to United States. Assigned to N2351B.
Where is Mode-S A21D90 registered?
Mode-S code A21D90 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 A21D90 broadcasting right now?
No active broadcast right now. Last signal was 19d ago.
Hex, octal, and decimal Mode-S codes: what's the difference?
The same 24-bit identifier expressed in different bases: hex A21D90, octal 50416620, decimal 10,624,400.
What flights does A21D90 operate?
Mode-S A21D90 has broadcast 1 distinct callsign, including N2351B.