Apparatus

Try JFK, AAL1290, BAW, or N225AN.

sensors Mode-S transponder

A4A439

ICAO 24-bit transponder address · allocated to United States

Currently assigned to N399AA · CIRRUS SR-22 · operated by JON BOYD

Hex
A4A439
Octal
51122071
Decimal
10,789,945
Country
US
Tail
N399AA
Type
SR22
No current signal · last broadcast 4h ago
Flights observed
218
Distinct callsigns
1
Country
US
Last broadcast
4h ago

Last known position

Most recent position reported by Mode-S A4A439.

Country allocation

The ICAO 24-bit address A4A439 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
N399AA - 218 2026-07-14

Recent flights last 50

DateFlightRouteTakeoffLandingDuration
2026-07-14 N399AA ISM → ISM Jul 14, 11:40 UTCJul 14, 12:45 UTC1h 5m
2026-07-11 N399AA - Jul 11, 19:45 UTCJul 11, 20:40 UTC55m
2026-07-11 N399AA - Jul 11, 17:55 UTCJul 11, 19:10 UTC1h 15m
2026-07-10 N399AA ISM → ISM Jul 10, 17:55 UTCJul 10, 19:00 UTC1h 5m
2026-07-10 N399AA ISM → ISM Jul 10, 15:40 UTCJul 10, 16:35 UTC55m
2026-07-10 N399AA - Jul 10, 13:35 UTCJul 10, 14:50 UTC1h 15m
2026-07-09 N399AA - Jul 9, 19:15 UTCJul 9, 19:25 UTC10m
2026-07-08 N399AA - Jul 8, 17:50 UTCJul 8, 18:25 UTC35m
2026-07-08 N399AA - Jul 8, 15:45 UTCJul 8, 16:45 UTC1h 0m
2026-07-08 N399AA - Jul 8, 13:55 UTCJul 8, 14:55 UTC1h 0m
2026-07-07 N399AA - Jul 7, 14:25 UTCJul 7, 15:10 UTC45m
2026-07-07 N399AA ISM → ISM Jul 7, 11:50 UTCJul 7, 13:05 UTC1h 15m
2026-07-06 N399AA - Jul 6, 17:35 UTCJul 6, 18:40 UTC1h 5m
2026-07-06 N399AA - Jul 6, 15:45 UTCJul 6, 16:30 UTC45m
2026-07-06 N399AA - Jul 6, 11:45 UTCJul 6, 12:30 UTC45m
2026-07-05 N399AA - Jul 5, 16:05 UTCJul 5, 16:30 UTC25m
2026-07-05 N399AA - Jul 5, 11:45 UTCJul 5, 12:35 UTC50m
2026-07-03 N399AA - Jul 3, 17:10 UTCJul 3, 21:45 UTC4h 35m
2026-07-03 N399AA - Jul 3, 14:20 UTCJul 3, 15:20 UTC1h 0m
2026-07-02 N399AA - Jul 2, 19:40 UTCJul 2, 20:30 UTC50m
2026-07-02 N399AA - Jul 2, 14:35 UTCJul 2, 15:40 UTC1h 5m
2026-07-02 N399AA - Jul 2, 01:20 UTCJul 2, 01:35 UTC15m
2026-07-01 N399AA ISM → ISM Jul 1, 19:15 UTCJul 1, 19:30 UTC15m
2026-07-01 N399AA - Jul 1, 15:30 UTCJul 1, 15:50 UTC20m
2026-07-01 N399AA - Jul 1, 13:55 UTCJul 1, 14:30 UTC35m
2026-07-01 N399AA - Jul 1, 11:45 UTCJul 1, 12:50 UTC1h 5m
2026-06-30 N399AA ISM → ISM Jun 30, 17:05 UTCJun 30, 17:50 UTC45m
2026-06-30 N399AA - Jun 30, 15:55 UTCJun 30, 16:30 UTC35m
2026-06-30 N399AA ISM → ISM Jun 30, 13:20 UTCJun 30, 14:30 UTC1h 10m
2026-06-29 N399AA - Jun 29, 17:49 UTCJun 29, 18:44 UTC55m
2026-06-29 N399AA - Jun 29, 16:00 UTCJun 29, 16:59 UTC1h 0m
2026-06-29 N399AA - Jun 29, 13:39 UTCJun 29, 14:50 UTC1h 10m
2026-06-28 N399AA - Jun 28, 15:29 UTCJun 28, 16:29 UTC1h 0m
2026-06-27 N399AA - Jun 27, 14:09 UTCJun 27, 14:54 UTC45m
2026-06-26 N399AA - Jun 26, 16:49 UTCJun 26, 17:44 UTC55m
2026-06-26 N399AA ISM → ISM Jun 26, 13:49 UTCJun 26, 14:35 UTC45m
2026-06-26 N399AA ISM → ISM Jun 26, 12:00 UTCJun 26, 12:55 UTC55m
2026-06-25 N399AA ISM → ISM Jun 25, 17:49 UTCJun 25, 18:34 UTC45m
2026-06-25 N399AA - Jun 25, 15:40 UTCJun 25, 16:35 UTC55m
2026-06-25 N399AA ISM → ISM Jun 25, 13:29 UTCJun 25, 14:50 UTC1h 20m
2026-06-24 N399AA - Jun 24, 13:54 UTCJun 24, 14:45 UTC50m
2026-06-24 N399AA - Jun 24, 12:20 UTCJun 24, 12:54 UTC35m
2026-06-23 N399AA - Jun 23, 19:39 UTCJun 23, 20:40 UTC1h 0m
2026-06-23 N399AA - Jun 23, 17:39 UTCJun 23, 18:55 UTC1h 15m
2026-06-23 N399AA - Jun 23, 15:30 UTCJun 23, 16:20 UTC50m
2026-06-23 N399AA ISM → ISM Jun 23, 13:34 UTCJun 23, 14:39 UTC1h 5m
2026-06-23 N399AA ISM → ISM Jun 23, 01:25 UTCJun 23, 01:45 UTC20m
2026-06-22 N399AA - Jun 22, 22:19 UTCJun 22, 22:54 UTC35m
2026-06-22 N399AA - Jun 22, 21:45 UTCJun 22, 22:15 UTC30m
2026-06-22 N399AA - Jun 22, 19:49 UTCJun 22, 20:34 UTC45m

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 N399AA page for operator, model, and routing details .

Mode-S A4A439 frequently asked

What is Mode-S code A4A439?
A4A439 is an ICAO 24-bit transponder address. Allocated to United States. Assigned to N399AA.
Where is Mode-S A4A439 registered?
Mode-S code A4A439 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 A4A439 broadcasting right now?
No active broadcast right now. Last signal was 4h ago.
Hex, octal, and decimal Mode-S codes: what's the difference?
The same 24-bit identifier expressed in different bases: hex A4A439, octal 51122071, decimal 10,789,945.
What flights does A4A439 operate?
Mode-S A4A439 has broadcast 1 distinct callsign, including N399AA.