Apparatus

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sensors Mode-S transponder

A4FFC0

ICAO 24-bit transponder address · allocated to United States

Currently assigned to N421EF · SCHLEICHER ASK-21 · operated by SOARING SOCIETY OF BOULDER

Hex
A4FFC0
Octal
51177700
Decimal
10,813,376
Country
US
Tail
N421EF
Type
AS21
No current signal · last broadcast 13h ago
Flights observed
72
Distinct callsigns
1
Country
US
Last broadcast
13h ago

Last known position

Most recent position reported by Mode-S A4FFC0.

Country allocation

The ICAO 24-bit address A4FFC0 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
N421EF - 72 2026-07-13

Recent flights last 50

DateFlightRouteTakeoffLandingDuration
2026-07-13 N421EF WBU → WBU Jul 13, 16:10 UTCJul 13, 16:50 UTC40m
2026-07-12 N421EF WBU → WBU Jul 12, 19:01 UTCJul 12, 19:10 UTC10m
2026-07-10 N421EF WBU → WBU Jul 10, 16:55 UTCJul 10, 18:05 UTC1h 10m
2026-07-09 N421EF WBU → WBU Jul 9, 16:00 UTCJul 9, 17:15 UTC1h 15m
2026-07-06 N421EF WBU → WBU Jul 6, 18:15 UTCJul 6, 19:50 UTC1h 35m
2026-07-06 N421EF WBU → WBU Jul 6, 16:15 UTCJul 6, 17:00 UTC45m
2026-07-05 N421EF WBU → WBU Jul 5, 18:15 UTCJul 5, 20:05 UTC1h 50m
2026-07-04 N421EF WBU → WBU Jul 4, 17:05 UTCJul 4, 19:15 UTC2h 10m
2026-07-01 N421EF WBU → WBU Jul 1, 18:05 UTCJul 1, 19:25 UTC1h 20m
2026-07-01 N421EF WBU → WBU Jul 1, 17:00 UTCJul 1, 17:10 UTC10m
2026-07-01 N421EF WBU → WBU Jul 1, 15:35 UTCJul 1, 15:50 UTC15m
2026-06-30 N421EF WBU → WBU Jun 30, 18:00 UTCJun 30, 20:25 UTC2h 25m
2026-06-28 N421EF WBU → WBU Jun 28, 20:29 UTCJun 28, 20:45 UTC15m
2026-06-26 N421EF WBU → WBU Jun 26, 18:44 UTCJun 26, 19:09 UTC25m
2026-06-20 N421EF WBU → WBU Jun 20, 17:34 UTCJun 20, 17:59 UTC25m
2026-06-18 N421EF WBU → WBU Jun 18, 15:35 UTCJun 18, 16:00 UTC25m
2026-06-17 N421EF WBU → WBU Jun 17, 16:40 UTCJun 17, 18:10 UTC1h 30m
2026-06-16 N421EF WBU → WBU Jun 16, 18:45 UTCJun 16, 19:10 UTC25m
2026-06-16 N421EF WBU → WBU Jun 16, 15:50 UTCJun 16, 17:59 UTC2h 10m
2026-06-15 N421EF WBU → WBU Jun 15, 19:05 UTCJun 15, 20:00 UTC55m
2026-06-12 N421EF WBU → WBU Jun 12, 15:15 UTCJun 12, 16:05 UTC50m
2026-06-11 N421EF - Jun 11, 15:35 UTCJun 11, 17:05 UTC1h 30m
2026-06-09 N421EF WBU → WBU Jun 9, 16:45 UTCJun 9, 17:15 UTC30m
2026-06-09 N421EF WBU → WBU Jun 9, 15:05 UTCJun 9, 15:50 UTC45m
2026-06-06 N421EF WBU → WBU Jun 6, 15:34 UTCJun 6, 16:10 UTC35m
2026-06-05 N421EF WBU → WBU Jun 5, 19:50 UTCJun 5, 20:35 UTC45m
2026-06-05 N421EF WBU → WBU Jun 5, 17:25 UTCJun 5, 17:55 UTC30m
2026-06-05 N421EF WBU → WBU Jun 5, 16:05 UTCJun 5, 16:50 UTC45m
2026-06-04 N421EF WBU → WBU Jun 4, 19:30 UTCJun 4, 20:00 UTC30m
2026-06-03 N421EF WBU → WBU Jun 3, 18:30 UTCJun 3, 20:05 UTC1h 35m
2026-06-03 N421EF WBU → WBU Jun 3, 16:10 UTCJun 3, 17:35 UTC1h 25m
2026-05-30 N421EF WBU → WBU May 30, 17:20 UTCMay 30, 18:10 UTC50m
2026-05-30 N421EF WBU → WBU May 30, 16:05 UTCMay 30, 16:35 UTC30m
2026-05-29 N421EF WBU → WBU May 29, 17:05 UTCMay 29, 18:30 UTC1h 25m
2026-05-27 N421EF WBU → WBU May 27, 17:10 UTCMay 27, 19:20 UTC2h 10m
2026-05-26 N421EF WBU → WBU May 26, 16:30 UTCMay 26, 18:10 UTC1h 40m
2026-05-25 N421EF WBU → WBU May 25, 15:20 UTCMay 25, 15:35 UTC15m
2026-05-24 N421EF WBU → WBU May 24, 16:10 UTCMay 24, 17:00 UTC50m
2026-05-23 N421EF WBU → WBU May 23, 16:25 UTCMay 23, 18:05 UTC1h 40m
2026-05-22 N421EF WBU → WBU May 22, 15:55 UTCMay 22, 17:50 UTC1h 55m
2026-05-21 N421EF - May 21, 17:10 UTCMay 21, 18:40 UTC1h 30m
2026-05-20 N421EF WBU → WBU May 20, 15:45 UTCMay 20, 16:10 UTC25m
2026-05-16 N421EF WBU → WBU May 16, 18:35 UTCMay 16, 19:35 UTC1h 0m
2026-05-16 N421EF WBU → WBU May 16, 15:40 UTCMay 16, 15:55 UTC15m
2026-05-15 N421EF - May 15, 17:30 UTCMay 15, 18:55 UTC1h 25m
2026-05-15 N421EF WBU → WBU May 15, 15:45 UTCMay 15, 16:10 UTC25m
2026-05-14 N421EF - May 14, 17:40 UTCMay 14, 18:25 UTC45m
2026-05-14 N421EF WBU → WBU May 14, 16:15 UTCMay 14, 17:05 UTC50m
2026-05-12 N421EF - May 12, 18:05 UTCMay 12, 20:30 UTC2h 25m
2026-05-12 N421EF WBU → WBU May 12, 15:40 UTCMay 12, 16:20 UTC40m

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 N421EF page for operator, model, and routing details .

Mode-S A4FFC0 frequently asked

What is Mode-S code A4FFC0?
A4FFC0 is an ICAO 24-bit transponder address. Allocated to United States. Assigned to N421EF.
Where is Mode-S A4FFC0 registered?
Mode-S code A4FFC0 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 A4FFC0 broadcasting right now?
No active broadcast right now. Last signal was 13h ago.
Hex, octal, and decimal Mode-S codes: what's the difference?
The same 24-bit identifier expressed in different bases: hex A4FFC0, octal 51177700, decimal 10,813,376.
What flights does A4FFC0 operate?
Mode-S A4FFC0 has broadcast 1 distinct callsign, including N421EF.