Apparatus

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sensors Mode-S transponder

A44521

ICAO 24-bit transponder address · allocated to United States

Currently assigned to N37409 · BOEING 737-900 · operated by UNITED AIRLINES INC

Hex
A44521
Octal
51042441
Decimal
10,765,601
Country
US
Tail
N37409
Type
B739
No current signal · last broadcast Jul 26, 22:15 UTC
Flights observed
465
Distinct callsigns
20
Country
US
Last broadcast
Jul 26, 22:15 UTC

Last known position

Most recent position reported by Mode-S A44521.

Country allocation

The ICAO 24-bit address A44521 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
UAL2124 United Airlines 14 2026-07-26
UAL1563 - 14 2026-07-16
UAL1927 - 13 2026-07-15
UAL496 - 12 2026-06-22
UAL315 United Airlines 12 2026-06-30
UAL1361 - 12 2026-07-12
UAL740 - 11 2026-07-15
UAL2293 United Airlines 11 2026-07-24
UAL2215 - 11 2026-06-23
UAL1936 - 11 2026-07-16
UAL2310 - 10 2026-07-20
UAL2250 - 10 2026-06-30
UAL2662 - 9 2026-07-17
UAL1444 - 9 2026-06-30
UAL2833 - 8 2026-07-12
UAL2304 United Airlines 8 2026-07-01
UAL1949 United Airlines 8 2026-07-25
UAL1872 - 8 2026-07-18
UAL1687 - 8 2026-06-23
UAL1345 - 8 2026-06-14

Recent flights last 50

DateFlightRouteTakeoffLandingDuration
2026-07-26 UAL2237 ORD → EWR Jul 26, 19:45 UTCJul 26, 22:15 UTC2h 30m
2026-07-26 UAL2491 SFO → DEN Jul 26, 15:35 UTCJul 26, 18:05 UTC2h 30m
2026-07-26 UAL2124 PDX → SFO Jul 26, 12:30 UTCJul 26, 13:25 UTC55m
2026-07-26 UAL1696 SFO → RNO Jul 26, 01:40 UTCJul 26, 02:30 UTC50m
2026-07-25 UAL1949 ORD → DCA Jul 25, 20:25 UTCJul 25, 23:50 UTC3h 25m
2026-07-25 UAL1949 ORD → DCA Jul 25, 20:26 UTCJul 25, 23:43 UTC3h 17m
2026-07-25 UAL2773 HNL → ORD Jul 25, 15:25 UTCJul 25, 18:40 UTC3h 15m
2026-07-25 UAL2773 HNL → ORD Jul 25, 15:24 UTCJul 25, 18:35 UTC3h 11m
2026-07-25 UAL396 HNL → SFO Jul 25, 11:40 UTCJul 25, 13:10 UTC1h 30m
2026-07-25 UAL1326 SFO → BNA Jul 25, 01:55 UTCJul 25, 03:20 UTC1h 25m
2026-07-25 UAL1326 SFO → BNA Jul 25, 01:55 UTCJul 25, 03:19 UTC1h 24m
2026-07-24 UAL2293 JAX → EWR Jul 24, 19:15 UTCJul 24, 22:15 UTC3h 0m
2026-07-24 UAL2293 JAX → EWR Jul 24, 19:15 UTCJul 24, 23:02 UTC3h 47m
2026-07-24 UAL2654 BNA → SFO Jul 24, 13:20 UTCJul 24, 17:30 UTC4h 10m
2026-07-22 UAL2840 GUM → SFO Jul 22, 10:25 UTCJul 22, 11:50 UTC1h 25m
2026-07-21 UAL1971 EWR → SAT Jul 21, 19:35 UTCJul 21, 22:15 UTC2h 40m
2026-07-21 UAL1971 EWR → SAT Jul 21, 19:40 UTCJul 21, 22:10 UTC2h 30m
2026-07-21 UAL1493 IAH → DEN Jul 21, 16:15 UTCJul 21, 18:10 UTC1h 55m
2026-07-21 UAL2245 IAH → MCO Jul 21, 12:35 UTCJul 21, 14:35 UTC2h 0m
2026-07-21 UAL1885 SLC → SFO Jul 21, 01:55 UTCJul 21, 04:15 UTC2h 20m
2026-07-20 UAL1507 - Jul 20, 22:30 UTCJul 21, 00:45 UTC2h 15m
2026-07-20 UAL2406 LAX → SFO Jul 20, 18:40 UTCJul 20, 20:45 UTC2h 5m
2026-07-20 UAL2310 - Jul 20, 14:50 UTCJul 20, 16:55 UTC2h 5m
2026-07-20 UAL2310 IAH → MCO Jul 20, 14:50 UTCJul 20, 16:50 UTC2h 0m
2026-07-20 UAL1898 BWI → IAH Jul 20, 10:20 UTCJul 20, 12:55 UTC2h 35m
2026-07-20 UAL1795 - Jul 20, 00:05 UTCJul 20, 03:15 UTC3h 10m
2026-07-19 UAL2237 ORD → EWR Jul 19, 19:20 UTCJul 19, 22:10 UTC2h 50m
2026-07-19 UAL2491 - Jul 19, 14:45 UTCJul 19, 17:25 UTC2h 40m
2026-07-19 UAL2491 IAH → SAN Jul 19, 14:50 UTCJul 19, 17:21 UTC2h 31m
2026-07-19 UAL2124 - Jul 19, 12:25 UTCJul 19, 13:15 UTC50m
2026-07-19 UAL8219 - Jul 19, 01:55 UTCJul 19, 02:45 UTC50m
2026-07-18 UAL1949 ORD → DCA Jul 18, 20:35 UTCJul 19, 00:05 UTC3h 30m
2026-07-18 UAL2773 - Jul 18, 15:20 UTCJul 18, 18:40 UTC3h 20m
2026-07-18 UAL396 - Jul 18, 11:40 UTCJul 18, 13:15 UTC1h 35m
2026-07-18 UAL1326 SFO → BNA Jul 18, 03:40 UTCJul 18, 05:10 UTC1h 30m
2026-07-18 UAL1872 - Jul 18, 00:04 UTCJul 18, 02:09 UTC2h 5m
2026-07-17 UAL2662 - Jul 17, 21:25 UTCJul 17, 21:50 UTC25m
2026-07-17 UAL2662 - Jul 17, 17:44 UTCJul 17, 20:10 UTC2h 25m
2026-07-17 UAL2863 - Jul 17, 12:30 UTCJul 17, 15:49 UTC3h 20m
2026-07-17 UAL1148 DEN → BOS Jul 17, 02:39 UTCJul 17, 06:00 UTC3h 20m
2026-07-16 UAL1872 - Jul 16, 22:59 UTCJul 17, 00:50 UTC1h 50m
2026-07-16 UAL2662 TPA → MCO Jul 16, 21:15 UTCJul 16, 21:40 UTC25m
2026-07-16 UAL2662 - Jul 16, 17:54 UTCJul 16, 20:00 UTC2h 5m
2026-07-16 UAL1936 - Jul 16, 13:10 UTCJul 16, 16:15 UTC3h 5m
2026-07-16 UAL1563 - Jul 16, 01:55 UTCJul 16, 04:40 UTC2h 45m
2026-07-16 UAL1563 IAH → ONT Jul 16, 02:00 UTCJul 16, 04:42 UTC2h 42m
2026-07-15 UAL1927 - Jul 15, 20:15 UTCJul 16, 00:00 UTC3h 45m
2026-07-15 UAL740 - Jul 15, 14:50 UTCJul 15, 18:30 UTC3h 40m
2026-07-15 UAL740 IAH → PDX Jul 15, 14:50 UTCJul 15, 18:27 UTC3h 37m
2026-07-14 UAL2237 - Jul 14, 19:55 UTCJul 14, 22:40 UTC2h 45m

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 N37409 page for operator, model, and routing details .

Mode-S A44521 frequently asked

What is Mode-S code A44521?
A44521 is an ICAO 24-bit transponder address. Allocated to United States. Assigned to N37409.
Where is Mode-S A44521 registered?
Mode-S code A44521 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 A44521 broadcasting right now?
No active broadcast right now. Last signal was Jul 26, 22:15 UTC.
Hex, octal, and decimal Mode-S codes: what's the difference?
The same 24-bit identifier expressed in different bases: hex A44521, octal 51042441, decimal 10,765,601.
What flights does A44521 operate?
Mode-S A44521 has broadcast 20 distinct callsigns, including UAL2124, UAL1563, UAL1927, UAL496, UAL315.