Apparatus

Try JFK, AAL1290, BAW, or N225AN.

sensors Mode-S transponder

A22539

ICAO 24-bit transponder address · allocated to United States

Currently assigned to N23721 · BOEING 737-700 · operated by UNITED AIRLINES INC

Hex
A22539
Octal
50422471
Decimal
10,626,361
Country
US
Tail
N23721
Type
B737
No current signal · last broadcast Jul 26, 22:15 UTC
Flights observed
449
Distinct callsigns
20
Country
US
Last broadcast
Jul 26, 22:15 UTC

Last known position

Most recent position reported by Mode-S A22539.

Country allocation

The ICAO 24-bit address A22539 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
UAL410 United Airlines 8 2026-07-22
UAL2612 - 8 2026-07-08
UAL1106 United Airlines 8 2026-07-24
UAL2468 United Airlines 6 2026-07-08
UAL2037 United Airlines 6 2026-07-24
UAL1869 United Airlines 6 2026-04-16
UAL1853 United Airlines 6 2026-07-23
UAL1207 - 6 2026-07-06
UAL1144 - 6 2026-07-06
UAL752 - 5 2026-06-26
UAL480 United Airlines 5 2026-06-03
UAL2256 United Airlines 5 2026-07-22
UAL2186 - 5 2026-06-30
UAL2178 United Airlines 5 2026-07-21
UAL1690 - 5 2026-06-29
UAL1477 - 5 2026-07-21
UAL722 United Airlines 4 2026-06-03
UAL654 - 4 2026-06-26
UAL630 - 4 2026-06-25
UAL2485 - 4 2026-06-25

Recent flights last 50

DateFlightRouteTakeoffLandingDuration
2026-07-26 UAL1381 IAH → SAN Jul 26, 20:55 UTCJul 26, 22:15 UTC1h 20m
2026-07-26 UAL2670 ORD → CLE Jul 26, 15:10 UTCJul 26, 17:45 UTC2h 35m
2026-07-26 UAL1201 SAN → SFO Jul 26, 00:05 UTCJul 26, 13:00 UTC12h 56m
2026-07-25 UAL2050 SFO → DEN Jul 25, 19:10 UTCJul 25, 22:00 UTC2h 50m
2026-07-25 UAL1383 IAH → SFO Jul 25, 13:40 UTCJul 25, 16:25 UTC2h 45m
2026-07-24 UAL1066 MEX → EWR Jul 24, 22:15 UTCJul 25, 01:25 UTC3h 10m
2026-07-24 UAL2181 MSP → ORD Jul 24, 17:30 UTCJul 24, 20:45 UTC3h 15m
2026-07-24 UAL2037 LGA → ORD Jul 24, 13:50 UTCJul 24, 15:00 UTC1h 10m
2026-07-24 UAL1106 ORD → DFW Jul 24, 03:20 UTCJul 24, 04:15 UTC55m
2026-07-24 UAL1106 ORD → DFW Jul 24, 03:25 UTCJul 24, 04:29 UTC1h 4m
2026-07-23 UAL1853 IAH → SFO Jul 23, 22:15 UTCJul 23, 23:07 UTC52m
2026-07-23 UAL1853 IAH → SFO Jul 23, 22:10 UTCJul 23, 23:15 UTC1h 5m
2026-07-23 UAL1852 LGA → ORD Jul 23, 19:45 UTCJul 23, 20:50 UTC1h 5m
2026-07-23 UAL1478 SEA → SFO Jul 23, 14:20 UTCJul 23, 18:25 UTC4h 5m
2026-07-22 UAL241 BNA → EWR Jul 22, 22:10 UTCJul 23, 02:10 UTC4h 0m
2026-07-22 UAL2026 MTY → IAH Jul 22, 18:20 UTCJul 22, 19:25 UTC1h 5m
2026-07-22 UAL2256 IAH → MTY Jul 22, 15:28 UTCJul 22, 16:15 UTC47m
2026-07-22 UAL2256 IAH → MTY Jul 22, 15:10 UTCJul 22, 16:15 UTC1h 5m
2026-07-22 UAL410 LAX → LAS Jul 22, 12:55 UTCJul 22, 13:35 UTC40m
2026-07-22 UAL410 LAX → LAS Jul 22, 12:59 UTCJul 22, 13:31 UTC32m
2026-07-21 UAL1477 - Jul 21, 23:55 UTCJul 22, 00:30 UTC35m
2026-07-21 UAL2178 QRO → IAH Jul 21, 17:50 UTCJul 21, 22:30 UTC4h 40m
2026-07-21 UAL1361 SNA → IAH Jul 21, 12:40 UTCJul 21, 16:05 UTC3h 25m
2026-07-20 UAL1680 MIA → EWR Jul 20, 23:35 UTCJul 21, 02:45 UTC3h 10m
2026-07-20 UAL1381 IAH → SAN Jul 20, 19:20 UTCJul 20, 21:45 UTC2h 25m
2026-07-20 UAL2670 ORD → CLE Jul 20, 15:10 UTCJul 20, 17:45 UTC2h 35m
2026-07-20 UAL396 BNA → IAH Jul 20, 11:40 UTCJul 20, 13:10 UTC1h 30m
2026-07-20 UAL396 BNA → IAH Jul 20, 11:46 UTCJul 20, 13:08 UTC1h 22m
2026-07-20 UAL8104 - Jul 20, 02:15 UTCJul 20, 03:50 UTC1h 35m
2026-07-19 UAL2178 QRO → IAH Jul 19, 19:40 UTCJul 20, 00:05 UTC4h 25m
2026-07-19 UAL1478 - Jul 19, 14:20 UTCJul 19, 18:10 UTC3h 50m
2026-07-18 UAL241 BNA → EWR Jul 18, 22:05 UTCJul 19, 02:00 UTC3h 55m
2026-07-18 UAL2026 MTY → IAH Jul 18, 18:25 UTCJul 18, 19:30 UTC1h 5m
2026-07-18 UAL2256 IAH → MTY Jul 18, 15:30 UTCJul 18, 16:35 UTC1h 5m
2026-07-18 UAL1409 - Jul 18, 10:20 UTCJul 18, 13:50 UTC3h 30m
2026-07-17 UAL2161 - Jul 17, 21:50 UTCJul 18, 01:20 UTC3h 30m
2026-07-17 UAL2026 MTY → IAH Jul 17, 18:40 UTCJul 17, 19:45 UTC1h 5m
2026-07-17 UAL2256 IAH → MTY Jul 17, 16:10 UTCJul 17, 17:20 UTC1h 10m
2026-07-17 UAL2256 IAH → MTY Jul 17, 16:17 UTCJul 17, 17:12 UTC55m
2026-07-17 UAL2037 - Jul 17, 13:50 UTCJul 17, 14:55 UTC1h 5m
2026-07-17 UAL1106 ORD → DFW Jul 17, 03:39 UTCJul 17, 04:39 UTC1h 0m
2026-07-16 UAL1066 - Jul 16, 22:25 UTCJul 17, 01:35 UTC3h 10m
2026-07-16 UAL2181 - Jul 16, 17:30 UTCJul 16, 20:39 UTC3h 10m
2026-07-16 UAL2181 IAH → LGA Jul 16, 17:21 UTCJul 16, 20:38 UTC3h 17m
2026-07-16 UAL1361 - Jul 16, 12:40 UTCJul 16, 15:55 UTC3h 15m
2026-07-15 UAL1680 - Jul 15, 23:35 UTCJul 16, 02:45 UTC3h 10m
2026-07-14 UAL1066 - Jul 14, 22:05 UTCJul 15, 01:35 UTC3h 29m
2026-07-14 UAL2181 - Jul 14, 17:30 UTCJul 14, 20:45 UTC3h 15m
2026-07-14 UAL2037 - Jul 14, 13:55 UTCJul 14, 15:15 UTC1h 20m
2026-07-14 UAL1106 - Jul 14, 02:15 UTCJul 14, 03:30 UTC1h 15m

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 N23721 page for operator, model, and routing details .

Mode-S A22539 frequently asked

What is Mode-S code A22539?
A22539 is an ICAO 24-bit transponder address. Allocated to United States. Assigned to N23721.
Where is Mode-S A22539 registered?
Mode-S code A22539 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 A22539 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 A22539, octal 50422471, decimal 10,626,361.
What flights does A22539 operate?
Mode-S A22539 has broadcast 20 distinct callsigns, including UAL410, UAL2612, UAL1106, UAL2468, UAL2037.