Apparatus

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sensors Mode-S transponder

A1239D

ICAO 24-bit transponder address · allocated to United States

Currently assigned to N17245 · BOEING 737-800 · operated by UNITED AIRLINES INC

Hex
A1239D
Octal
50221635
Decimal
10,560,413
Country
US
Tail
N17245
Type
B738
Broadcasting now · callsign UAL1794 · 36,000 ft
Flights observed
112
Distinct callsigns
20
Country
US
Last broadcast
Jul 26, 19:40 UTC

Current position

A1239D is currently broadcasting. Map zoomed to live position.

Country allocation

The ICAO 24-bit address A1239D 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
UAL1006 - 4 2026-07-15
UAL737 - 3 2026-04-13
UAL1963 - 3 2026-04-17
UAL1217 United Airlines 3 2026-04-22
UAL8121 - 2 2026-07-10
UAL588 United Airlines 2 2026-04-22
UAL551 - 2 2026-04-16
UAL4199 - 2 2026-07-08
UAL401 - 2 2026-07-16
UAL3899 United Airlines 2 2026-07-26
UAL3898 - 2 2026-07-09
UAL3895 - 2 2026-07-17
UAL2742 United Airlines 2 2026-04-22
UAL2368 - 2 2026-04-17
UAL2338 United Airlines 2 2026-04-17
UAL230 United Airlines 2 2026-04-27
UAL2279 - 2 2026-04-13
UAL2145 United Airlines 2 2026-04-27
UAL1973 United Airlines 2 2026-04-23
UAL1854 United Airlines 2 2026-04-16

Recent flights last 50

DateFlightRouteTakeoffLandingDuration
2026-07-26 UAL692 SEA → ORD Jul 26, 16:40 UTCJul 26, 19:40 UTC3h 0m
2026-07-26 UAL1697 ATL → EWR Jul 26, 12:10 UTCJul 26, 15:30 UTC3h 20m
2026-07-26 UAL3899 IAD → EWR Jul 26, 02:30 UTCJul 26, 03:40 UTC1h 10m
2026-07-26 UAL3899 IAD → EWR Jul 26, 01:47 UTCJul 26, 03:38 UTC1h 51m
2026-07-17 UAL3895 IAH → AMA Jul 17, 02:38 UTCJul 17, 03:30 UTC52m
2026-07-17 UAL3895 - Jul 17, 02:20 UTCJul 17, 03:20 UTC1h 0m
2026-07-16 UAL401 - Jul 16, 23:05 UTCJul 17, 01:09 UTC2h 5m
2026-07-16 UAL401 - Jul 16, 22:45 UTCJul 16, 22:59 UTC15m
2026-07-16 UAL1737 - Jul 16, 17:49 UTCJul 16, 20:00 UTC2h 10m
2026-07-16 UAL1737 IAH → LIR Jul 16, 17:47 UTCJul 16, 20:44 UTC2h 57m
2026-07-16 UAL1318 - Jul 16, 13:30 UTCJul 16, 15:49 UTC2h 20m
2026-07-16 UAL233 - Jul 16, 07:05 UTCJul 16, 08:40 UTC1h 35m
2026-07-16 UAL1195 - Jul 16, 04:05 UTCJul 16, 05:20 UTC1h 15m
2026-07-15 UAL741 - Jul 15, 20:05 UTCJul 16, 01:40 UTC5h 35m
2026-07-15 UAL203 - Jul 15, 17:55 UTCJul 15, 18:35 UTC40m
2026-07-15 UAL1006 - Jul 15, 15:50 UTCJul 15, 16:40 UTC50m
2026-07-15 UAL1006 LAX → LAS Jul 15, 15:42 UTCJul 15, 16:35 UTC53m
2026-07-15 UAL1006 - Jul 15, 13:35 UTCJul 15, 14:00 UTC25m
2026-07-15 UAL2142 SFO → SAN Jul 15, 06:55 UTCJul 15, 08:10 UTC1h 15m
2026-07-14 UAL372 - Jul 14, 20:35 UTCJul 14, 21:30 UTC55m
2026-07-13 UAL1185 - Jul 13, 16:05 UTCJul 13, 22:15 UTC6h 10m
2026-07-13 UAL1006 - Jul 13, 13:45 UTCJul 13, 14:10 UTC25m
2026-07-13 UAL594 - Jul 13, 06:10 UTCJul 13, 06:50 UTC40m
2026-07-12 UAL1546 - Jul 12, 23:40 UTCJul 13, 04:15 UTC4h 35m
2026-07-12 UAL2124 - Jul 12, 20:01 UTCJul 12, 21:25 UTC1h 25m
2026-07-12 UAL1968 YYC → ORD Jul 12, 14:45 UTCJul 12, 17:45 UTC3h 0m
2026-07-12 UAL1156 - Jul 12, 02:01 UTCJul 12, 05:01 UTC3h 0m
2026-07-11 UAL329 - Jul 11, 22:10 UTCJul 12, 00:20 UTC2h 10m
2026-07-11 UAL2418 DEN → BTV Jul 11, 17:00 UTCJul 11, 20:15 UTC3h 15m
2026-07-11 UAL2750 - Jul 11, 12:10 UTCJul 11, 15:40 UTC3h 30m
2026-07-11 UAL1662 - Jul 11, 02:15 UTCJul 11, 05:15 UTC3h 0m
2026-07-10 UAL475 - Jul 10, 21:10 UTCJul 10, 23:25 UTC2h 15m
2026-07-10 UAL8121 DEN → YEG Jul 10, 17:59 UTCJul 10, 19:50 UTC1h 51m
2026-07-10 UAL8121 - Jul 10, 17:50 UTCJul 10, 19:15 UTC1h 25m
2026-07-10 UAL318 RSW → DEN Jul 10, 12:15 UTCJul 10, 15:40 UTC3h 25m
2026-07-10 UAL2348 DEN → RSW Jul 10, 00:35 UTCJul 10, 03:55 UTC3h 20m
2026-07-09 UAL3898 - Jul 9, 18:00 UTCJul 9, 23:05 UTC5h 5m
2026-07-09 UAL3898 MIA → DEN Jul 9, 17:43 UTCJul 9, 23:00 UTC5h 17m
2026-07-08 UAL4199 - Jul 8, 14:05 UTCJul 8, 16:05 UTC2h 0m
2026-07-08 UAL4199 MIA → MIA Jul 8, 14:18 UTCJul 8, 16:05 UTC1h 47m
2026-05-05 UAL3851 FRA → SFO May 5, 23:30 UTCMay 6, 01:40 UTC2h 10m
2026-04-28 UAL2270 LAS → IAH Apr 28, 12:10 UTCApr 28, 13:25 UTC1h 15m
2026-04-27 UAL680 SAT → DEN Apr 27, 23:55 UTCApr 28, 03:05 UTC3h 10m
2026-04-27 UAL1961 LAS → IAD Apr 27, 20:15 UTCApr 27, 22:10 UTC1h 55m
2026-04-27 UAL2145 MFR → SFO Apr 27, 14:42 UTCApr 27, 18:30 UTC3h 48m
2026-04-27 UAL2145 MFR → SFO Apr 27, 14:30 UTCApr 27, 18:35 UTC4h 5m
2026-04-27 UAL230 BON → EWR Apr 27, 11:16 UTCApr 27, 12:32 UTC1h 16m
2026-04-27 UAL230 BON → EWR Apr 27, 11:20 UTCApr 27, 12:45 UTC1h 25m
2026-04-27 UAL1564 BOS → ORD Apr 27, 03:20 UTCApr 27, 04:25 UTC1h 5m
2026-04-26 UAL598 EWR → CLE Apr 26, 23:10 UTCApr 27, 01:05 UTC1h 55m

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 N17245 page for operator, model, and routing details .

Mode-S A1239D frequently asked

What is Mode-S code A1239D?
A1239D is an ICAO 24-bit transponder address. Allocated to United States. Assigned to N17245.
Where is Mode-S A1239D registered?
Mode-S code A1239D 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 A1239D broadcasting right now?
Yes. Mode-S A1239D is currently airborne.
Hex, octal, and decimal Mode-S codes: what's the difference?
The same 24-bit identifier expressed in different bases: hex A1239D, octal 50221635, decimal 10,560,413.
What flights does A1239D operate?
Mode-S A1239D has broadcast 20 distinct callsigns, including UAL1006, UAL737, UAL1963, UAL1217, UAL8121.