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sensors Mode-S transponder

A5521C

ICAO 24-bit transponder address · allocated to United States

Currently assigned to N442AS · BOEING 737-900 · operated by ALASKA AIRLINES INC

Hex
A5521C
Octal
51251034
Decimal
10,834,460
Country
US
Tail
N442AS
Type
B739
No current signal · last broadcast 3h ago
Flights observed
401
Distinct callsigns
20
Country
US
Last broadcast
3h ago

Last known position

Most recent position reported by Mode-S A5521C.

Country allocation

The ICAO 24-bit address A5521C 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
ASA280 - 9 2026-06-30
ASA515 Alaska Airlines 7 2026-05-24
ASA298 - 5 2026-04-17
ASA748 - 4 2026-07-06
ASA577 Alaska Airlines 4 2026-05-10
ASA503 Alaska Airlines 4 2026-07-02
ASA478 Alaska Airlines 4 2026-05-12
ASA31 Alaska Airlines 4 2026-05-07
ASA299 Alaska Airlines 4 2026-06-03
ASA1397 Alaska Airlines 4 2026-05-10
ASA1330 Alaska Airlines 4 2026-05-20
ASA12 Alaska Airlines 4 2026-05-17
ASA682 - 3 2026-06-28
ASA657 Alaska Airlines 3 2026-05-30
ASA596 Alaska Airlines 3 2026-05-31
ASA587 Alaska Airlines 3 2026-07-09
ASA502 - 3 2026-04-13
ASA501 - 3 2026-06-29
ASA497 - 3 2026-06-28
ASA474 Alaska Airlines 3 2026-05-08

Recent flights last 50

DateFlightRouteTakeoffLandingDuration
2026-07-14 ASA366 LAS → SEA Jul 14, 04:50 UTCJul 14, 06:35 UTC1h 45m
2026-07-14 ASA1456 SEA → LAS Jul 14, 00:35 UTCJul 14, 02:50 UTC2h 15m
2026-07-13 ASA446 - Jul 13, 20:50 UTCJul 13, 22:50 UTC2h 0m
2026-07-13 ASA208 - Jul 13, 17:20 UTCJul 13, 19:10 UTC1h 50m
2026-07-13 ASA625 - Jul 13, 11:45 UTCJul 13, 15:45 UTC4h 0m
2026-07-13 ASA625 IND → SEA Jul 13, 11:54 UTCJul 13, 15:38 UTC3h 44m
2026-07-13 ASA624 SEA → IND Jul 13, 06:25 UTCJul 13, 10:05 UTC3h 40m
2026-07-13 ASA339 AUS → SEA Jul 13, 00:25 UTCJul 13, 04:15 UTC3h 50m
2026-07-12 ASA604 SEA → AUS Jul 12, 19:10 UTCJul 12, 23:00 UTC3h 50m
2026-07-12 ASA241 - Jul 12, 13:20 UTCJul 12, 17:10 UTC3h 50m
2026-07-12 ASA398 - Jul 12, 07:20 UTCJul 12, 11:01 UTC3h 40m
2026-07-12 ASA403 SMF → SEA Jul 12, 03:45 UTCJul 12, 05:01 UTC1h 15m
2026-07-12 ASA403 SMF → SEA Jul 12, 03:42 UTCJul 12, 04:51 UTC1h 9m
2026-07-12 ASA1622 PDX → SMF Jul 12, 01:15 UTCJul 12, 02:30 UTC1h 15m
2026-07-11 ASA325 ORD → PDX Jul 11, 19:45 UTCJul 11, 23:35 UTC3h 50m
2026-07-11 ASA325 ORD → PDX Jul 11, 19:50 UTCJul 11, 23:35 UTC3h 45m
2026-07-11 ASA1446 CUN → LAX Jul 11, 14:25 UTCJul 11, 17:41 UTC3h 16m
2026-07-11 ASA1446 CUN → LAX Jul 11, 14:25 UTCJul 11, 17:55 UTC3h 30m
2026-07-11 ASA1472 - Jul 11, 04:20 UTCJul 11, 06:45 UTC2h 25m
2026-07-10 ASA1375 - Jul 10, 23:45 UTCJul 11, 01:55 UTC2h 10m
2026-07-10 ASA1604 SFO → LAX Jul 10, 21:05 UTCJul 10, 22:00 UTC55m
2026-07-10 ASA227 JFK → SFO Jul 10, 14:00 UTCJul 10, 19:40 UTC5h 40m
2026-07-10 ASA22 SEA → JFK Jul 10, 06:50 UTCJul 10, 11:35 UTC4h 45m
2026-07-10 ASA544 PDX → SFO Jul 10, 01:35 UTCJul 10, 04:50 UTC3h 15m
2026-07-10 ASA544 PDX → SFO Jul 10, 01:35 UTCJul 10, 04:41 UTC3h 6m
2026-07-09 ASA659 LAX → SFO Jul 9, 21:18 UTCJul 10, 00:13 UTC2h 55m
2026-07-09 ASA659 LAX → SFO Jul 9, 21:10 UTCJul 10, 00:15 UTC3h 5m
2026-07-09 ASA587 ORD → SEA Jul 9, 04:10 UTCJul 9, 04:25 UTC15m
2026-07-09 ASA587 ORD → SEA Jul 9, 00:05 UTCJul 9, 03:51 UTC3h 46m
2026-07-09 ASA587 ORD → SEA Jul 9, 00:05 UTCJul 9, 04:25 UTC4h 20m
2026-07-07 ASA410 - Jul 7, 20:30 UTCJul 7, 23:55 UTC3h 25m
2026-07-07 ASA623 - Jul 7, 14:35 UTCJul 7, 18:45 UTC4h 10m
2026-07-07 ASA623 BNA → SEA Jul 7, 14:34 UTCJul 7, 18:38 UTC4h 4m
2026-07-07 ASA382 SEA → BNA Jul 7, 07:50 UTCJul 7, 11:45 UTC3h 55m
2026-07-06 ASA748 - Jul 6, 14:35 UTCJul 6, 16:40 UTC2h 5m
2026-07-06 ASA748 LAX → SEA Jul 6, 14:30 UTCJul 6, 16:33 UTC2h 3m
2026-07-06 ASA333 - Jul 6, 02:35 UTCJul 6, 04:00 UTC1h 25m
2026-07-05 ASA1326 - Jul 5, 22:35 UTCJul 5, 23:45 UTC1h 10m
2026-07-05 ASA1326 LAX → SJD Jul 5, 22:37 UTCJul 6, 00:37 UTC2h 0m
2026-07-05 ASA1331 - Jul 5, 07:20 UTCJul 5, 20:20 UTC13h 0m
2026-07-04 ASA763 - Jul 4, 22:10 UTCJul 5, 02:55 UTC4h 45m
2026-07-04 ASA1416 SJC → GDL Jul 4, 15:25 UTCJul 4, 20:25 UTC5h 0m
2026-07-04 ASA1411 - Jul 4, 03:05 UTCJul 4, 03:45 UTC40m
2026-07-03 ASA1411 - Jul 3, 23:10 UTCJul 3, 23:25 UTC15m
2026-07-03 ASA768 SEA → LAS Jul 3, 15:55 UTCJul 3, 21:10 UTC5h 15m
2026-07-03 ASA768 SEA → LAS Jul 3, 15:51 UTCJul 3, 21:09 UTC5h 18m
2026-07-02 ASA1523 - Jul 2, 23:55 UTCJul 3, 00:50 UTC55m
2026-07-02 ASA680 SEA → SFO Jul 2, 20:50 UTCJul 2, 22:25 UTC1h 35m
2026-07-02 ASA637 - Jul 2, 16:35 UTCJul 2, 19:15 UTC2h 40m
2026-07-02 ASA632 SEA → PHX Jul 2, 03:20 UTCJul 2, 05:40 UTC2h 20m

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 N442AS page for operator, model, and routing details .

Mode-S A5521C frequently asked

What is Mode-S code A5521C?
A5521C is an ICAO 24-bit transponder address. Allocated to United States. Assigned to N442AS.
Where is Mode-S A5521C registered?
Mode-S code A5521C 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 A5521C broadcasting right now?
No active broadcast right now. Last signal was 3h ago.
Hex, octal, and decimal Mode-S codes: what's the difference?
The same 24-bit identifier expressed in different bases: hex A5521C, octal 51251034, decimal 10,834,460.
What flights does A5521C operate?
Mode-S A5521C has broadcast 20 distinct callsigns, including ASA280, ASA515, ASA298, ASA748, ASA577.