Apparatus

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sensors Mode-S transponder

A4C821

ICAO 24-bit transponder address · allocated to United States

Currently assigned to N407RH · BELL 407 · operated by MARITIME HELICOPTERS INC

Hex
A4C821
Octal
51144041
Decimal
10,799,137
Country
US
Tail
N407RH
Type
B407
No current signal · last broadcast 15d ago
Flights observed
45
Distinct callsigns
1
Country
US
Last broadcast
15d ago

Last known position

Most recent position reported by Mode-S A4C821.

Country allocation

The ICAO 24-bit address A4C821 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
MHF407 - 45 2026-06-28

Recent flights last 45

DateFlightRouteTakeoffLandingDuration
2026-06-28 MHF407 - Jun 28, 17:50 UTCJun 28, 18:00 UTC10m
2026-06-27 MHF407 - Jun 27, 19:19 UTCJun 27, 19:45 UTC25m
2026-06-26 MHF407 - Jun 26, 21:15 UTCJun 26, 21:59 UTC45m
2026-06-26 MHF407 - Jun 26, 17:15 UTCJun 26, 17:50 UTC35m
2026-06-26 MHF407 - Jun 26, 00:59 UTCJun 26, 01:15 UTC15m
2026-06-25 MHF407 - Jun 25, 23:24 UTCJun 25, 23:39 UTC15m
2026-06-25 MHF407 - Jun 25, 22:14 UTCJun 25, 22:24 UTC10m
2026-06-25 MHF407 - Jun 25, 17:05 UTCJun 25, 17:14 UTC10m
2026-06-24 MHF407 MCG → MCG Jun 24, 21:44 UTCJun 24, 22:14 UTC30m
2026-06-24 MHF407 - Jun 24, 19:39 UTCJun 24, 19:49 UTC10m
2026-06-24 MHF407 - Jun 24, 16:29 UTCJun 24, 16:54 UTC25m
2026-06-23 MHF407 - Jun 23, 21:29 UTCJun 23, 21:49 UTC20m
2026-06-23 MHF407 - Jun 23, 16:24 UTCJun 23, 16:44 UTC20m
2026-06-22 MHF407 - Jun 22, 17:15 UTCJun 22, 17:25 UTC10m
2026-06-19 MHF407 - Jun 19, 22:24 UTCJun 19, 22:45 UTC20m
2026-06-19 MHF407 - Jun 19, 15:54 UTCJun 19, 16:14 UTC20m
2026-06-19 MHF407 - Jun 19, 00:49 UTCJun 19, 01:10 UTC20m
2026-06-18 MHF407 - Jun 18, 15:55 UTCJun 18, 16:15 UTC20m
2026-06-18 MHF407 - Jun 18, 01:20 UTCJun 18, 01:50 UTC30m
2026-06-17 MHF407 - Jun 17, 16:05 UTCJun 17, 16:25 UTC20m
2026-06-16 MHF407 - Jun 16, 20:10 UTCJun 16, 20:35 UTC25m
2026-06-16 MHF407 - Jun 16, 19:05 UTCJun 16, 19:30 UTC25m
2026-06-16 MHF407 - Jun 16, 17:30 UTCJun 16, 17:45 UTC15m
2026-06-16 MHF407 - Jun 16, 15:15 UTCJun 16, 17:10 UTC1h 55m
2026-06-11 MHF407 - Jun 11, 23:30 UTCJun 11, 23:55 UTC25m
2026-06-11 MHF407 - Jun 11, 17:35 UTCJun 11, 18:00 UTC25m
2026-06-11 MHF407 - Jun 11, 15:10 UTCJun 11, 15:30 UTC20m
2026-06-10 MHF407 MTX → MTX Jun 10, 19:20 UTCJun 10, 19:30 UTC10m
2026-06-06 MHF407 - Jun 6, 00:30 UTCJun 6, 00:40 UTC10m
2026-05-30 MHF407 - May 30, 04:25 UTCMay 30, 05:05 UTC40m
2026-05-16 MHF407 - May 16, 17:55 UTCMay 16, 18:05 UTC10m
2026-05-16 MHF407 - May 16, 16:55 UTCMay 16, 17:05 UTC10m
2026-05-15 MHF407 - May 15, 18:45 UTCMay 15, 18:55 UTC10m
2026-05-12 MHF407 - May 12, 19:15 UTCMay 12, 19:25 UTC10m
2026-05-02 MHF407 - May 2, 22:10 UTCMay 2, 22:20 UTC10m
2026-05-02 MHF407 - May 2, 21:20 UTCMay 2, 21:30 UTC10m
2026-04-30 MHF407 - Apr 30, 18:30 UTCApr 30, 18:45 UTC15m
2026-04-28 MHF407 - Apr 28, 21:55 UTCApr 28, 22:30 UTC35m
2026-04-28 MHF407 - Apr 28, 16:00 UTCApr 28, 17:40 UTC1h 40m
2026-04-22 MHF407 - Apr 22, 23:25 UTCApr 22, 23:55 UTC30m
2026-04-22 MHF407 - Apr 22, 17:10 UTCApr 22, 17:30 UTC20m
2026-04-15 MHF407 - Apr 15, 22:20 UTCApr 15, 22:40 UTC20m
2026-04-14 MHF407 - Apr 14, 18:55 UTCApr 14, 19:25 UTC30m
2026-04-14 MHF407 - Apr 14, 17:55 UTCApr 14, 18:05 UTC10m
2026-04-14 MHF407 - Apr 14, 16:55 UTCApr 14, 17:05 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.

Prefer a tail-number view? See the N407RH page for operator, model, and routing details .

Mode-S A4C821 frequently asked

What is Mode-S code A4C821?
A4C821 is an ICAO 24-bit transponder address. Allocated to United States. Assigned to N407RH.
Where is Mode-S A4C821 registered?
Mode-S code A4C821 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 A4C821 broadcasting right now?
No active broadcast right now. Last signal was 15d ago.
Hex, octal, and decimal Mode-S codes: what's the difference?
The same 24-bit identifier expressed in different bases: hex A4C821, octal 51144041, decimal 10,799,137.
What flights does A4C821 operate?
Mode-S A4C821 has broadcast 1 distinct callsign, including MHF407.