Apparatus

Try JFK, AAL1290, BAW, or N225AN.

sensors Mode-S transponder

A4B420

ICAO 24-bit transponder address · allocated to United States

Currently assigned to N402AS · BOEING 737-900 · operated by ALASKA AIRLINES INC

Hex
A4B420
Octal
51132040
Decimal
10,794,016
Country
US
Tail
N402AS
Type
B739
No current signal · last broadcast 8h ago
Flights observed
417
Distinct callsigns
20
Country
US
Last broadcast
8h ago

Last known position

Most recent position reported by Mode-S A4B420.

Country allocation

The ICAO 24-bit address A4B420 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 20 distinct

Callsign Airline Flights Last seen
ASA572 Alaska Airlines 7 2026-04-18
ASA349 Alaska Airlines 7 2026-05-09
ASA569 - 5 2026-07-12
ASA507 Alaska Airlines 5 2026-04-16
ASA623 - 4 2026-06-16
ASA618 - 4 2026-06-25
ASA563 - 4 2026-06-24
ASA500 - 4 2026-06-15
ASA494 - 4 2026-06-30
ASA365 - 4 2026-06-28
ASA304 Alaska Airlines 4 2026-06-19
ASA24 Alaska Airlines 4 2026-07-01
ASA1540 - 4 2026-07-09
ASA1385 Alaska Airlines 4 2026-06-04
ASA84 Alaska Airlines 3 2026-06-02
ASA735 Alaska Airlines 3 2026-06-02
ASA727 - 3 2026-06-22
ASA684 Alaska Airlines 3 2026-05-07
ASA676 - 3 2026-06-22
ASA673 Alaska Airlines 3 2026-04-18

Recent flights last 50

DateFlightRouteTakeoffLandingDuration
2026-07-14 ASA1375 - Jul 14, 00:25 UTCJul 14, 02:30 UTC2h 5m
2026-07-13 ASA502 - Jul 13, 20:30 UTCJul 13, 22:55 UTC2h 25m
2026-07-13 ASA338 BOS → SEA Jul 13, 13:30 UTCJul 13, 19:00 UTC5h 30m
2026-07-13 ASA536 SEA → BOS Jul 13, 06:45 UTCJul 13, 11:40 UTC4h 55m
2026-07-12 ASA569 MSY → SEA Jul 12, 22:55 UTCJul 13, 03:20 UTC4h 25m
2026-07-12 ASA568 SEA → MSY Jul 12, 17:20 UTCJul 12, 21:40 UTC4h 20m
2026-07-12 ASA302 - Jul 12, 11:10 UTCJul 12, 15:25 UTC4h 15m
2026-07-12 ASA298 - Jul 12, 05:15 UTCJul 12, 09:05 UTC3h 50m
2026-07-12 ASA1508 - Jul 12, 00:25 UTCJul 12, 03:40 UTC3h 15m
2026-07-11 ASA1507 SEA → FAI Jul 11, 20:15 UTCJul 11, 23:25 UTC3h 10m
2026-07-11 ASA47 - Jul 11, 15:10 UTCJul 11, 18:20 UTC3h 10m
2026-07-11 ASA47 ANC → SEA Jul 11, 15:10 UTCJul 11, 18:08 UTC2h 58m
2026-07-11 ASA1545 - Jul 11, 06:10 UTCJul 11, 11:50 UTC5h 40m
2026-07-11 ASA1493 - Jul 11, 00:30 UTCJul 11, 03:55 UTC3h 25m
2026-07-10 ASA551 DFW → SAN Jul 10, 20:00 UTCJul 10, 22:30 UTC2h 30m
2026-07-10 ASA340 SEA → DFW Jul 10, 15:10 UTCJul 10, 18:30 UTC3h 20m
2026-07-10 ASA403 SMF → SEA Jul 10, 03:45 UTCJul 10, 05:05 UTC1h 20m
2026-07-10 ASA1622 PDX → SMF Jul 10, 01:15 UTCJul 10, 02:25 UTC1h 10m
2026-07-10 ASA1622 PDX → SMF Jul 10, 01:13 UTCJul 10, 02:20 UTC1h 7m
2026-07-09 ASA267 ANC → PDX Jul 9, 20:00 UTCJul 9, 23:10 UTC3h 10m
2026-07-09 ASA1541 MSP → ANC Jul 9, 12:55 UTCJul 9, 18:40 UTC5h 45m
2026-07-09 ASA1540 - Jul 9, 06:05 UTCJul 9, 11:10 UTC5h 5m
2026-07-09 ASA1540 ANC → MSP Jul 9, 06:09 UTCJul 9, 10:58 UTC4h 49m
2026-07-09 ASA257 - Jul 9, 01:05 UTCJul 9, 02:40 UTC1h 35m
2026-07-08 ASA1558 ANC → ADK Jul 8, 20:15 UTCJul 8, 21:40 UTC1h 25m
2026-07-08 ASA1558 ANC → ADK Jul 8, 20:14 UTCJul 8, 22:47 UTC2h 33m
2026-07-08 ASA432 DEN → ANC Jul 8, 13:50 UTCJul 8, 18:45 UTC4h 55m
2026-07-08 ASA1627 PDX → DEN Jul 8, 01:25 UTCJul 8, 03:20 UTC1h 55m
2026-07-07 ASA756 LAS → PDX Jul 7, 21:40 UTCJul 7, 23:30 UTC1h 50m
2026-07-07 ASA757 - Jul 7, 18:25 UTCJul 7, 20:15 UTC1h 50m
2026-07-07 ASA1630 EWR → PDX Jul 7, 10:55 UTCJul 7, 16:05 UTC5h 10m
2026-07-07 ASA263 SEA → EWR Jul 7, 00:00 UTCJul 7, 04:50 UTC4h 50m
2026-07-06 ASA630 LAS → SFO Jul 6, 20:30 UTCJul 6, 22:00 UTC1h 30m
2026-07-06 ASA630 LAS → SFO Jul 6, 20:29 UTCJul 6, 22:01 UTC1h 32m
2026-07-06 ASA1607 LAX → SFO Jul 6, 18:10 UTCJul 6, 19:05 UTC55m
2026-07-06 ASA1611 GEG → LAX Jul 6, 13:30 UTCJul 6, 15:45 UTC2h 15m
2026-07-06 ASA1614 LAX → GEG Jul 6, 03:10 UTCJul 6, 05:10 UTC2h 0m
2026-07-05 ASA1418 LAX → GDL Jul 5, 17:30 UTCJul 6, 01:35 UTC8h 5m
2026-07-05 ASA1611 GEG → LAX Jul 5, 13:25 UTCJul 5, 15:45 UTC2h 20m
2026-07-05 ASA1356 PDX → GEG Jul 5, 05:05 UTCJul 5, 05:50 UTC45m
2026-07-04 ASA19 JFK → PDX Jul 4, 22:10 UTCJul 5, 03:35 UTC5h 25m
2026-07-04 ASA20 SFO → JFK Jul 4, 14:45 UTCJul 4, 20:00 UTC5h 15m
2026-07-04 ASA791 EWR → SEA Jul 4, 01:55 UTCJul 4, 03:40 UTC1h 45m
2026-07-03 ASA332 ANC → SEA Jul 3, 19:47 UTCJul 3, 22:21 UTC2h 34m
2026-07-03 ASA332 ANC → SEA Jul 3, 19:30 UTCJul 3, 22:30 UTC3h 0m
2026-07-03 ASA73 - Jul 3, 15:45 UTCJul 3, 17:05 UTC1h 20m
2026-07-03 ASA73 - Jul 3, 14:05 UTCJul 3, 14:20 UTC15m
2026-07-03 ASA70 - Jul 3, 06:30 UTCJul 3, 06:45 UTC15m
2026-07-03 ASA70 - Jul 3, 03:45 UTCJul 3, 04:55 UTC1h 10m
2026-07-03 ASA9664 SCC → ANC Jul 3, 00:55 UTCJul 3, 02:09 UTC1h 14m

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 N402AS page for operator, model, and routing details .

Mode-S A4B420 frequently asked

What is Mode-S code A4B420?
A4B420 is an ICAO 24-bit transponder address. Allocated to United States. Assigned to N402AS.
Where is Mode-S A4B420 registered?
Mode-S code A4B420 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 A4B420 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 A4B420, octal 51132040, decimal 10,794,016.
What flights does A4B420 operate?
Mode-S A4B420 has broadcast 20 distinct callsigns, including ASA572, ASA349, ASA569, ASA507, ASA623.