Apparatus

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sensors Mode-S transponder

A254D8

ICAO 24-bit transponder address · allocated to United States

Currently assigned to N24974 · BOEING 787-9 Dreamliner · operated by UNITED AIRLINES INC

Hex
A254D8
Octal
50452330
Decimal
10,638,552
Country
US
Tail
N24974
Type
B789
No current signal · last broadcast Jul 26, 22:00 UTC
Flights observed
224
Distinct callsigns
20
Country
US
Last broadcast
Jul 26, 22:00 UTC

Last known position

Most recent position reported by Mode-S A254D8.

Country allocation

The ICAO 24-bit address A254D8 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
UAL820 United Airlines 16 2026-05-21
UAL821 United Airlines 15 2026-05-21
UAL26 United Airlines 11 2026-07-25
UAL178 United Airlines 11 2026-07-26
UAL27 United Airlines 9 2026-07-24
UAL152 United Airlines 9 2026-05-24
UAL772 United Airlines 8 2026-05-23
UAL181 United Airlines 8 2026-07-24
UAL177 United Airlines 8 2026-07-26
UAL771 United Airlines 7 2026-05-22
UAL182 United Airlines 7 2026-07-23
UAL153 United Airlines 7 2026-05-25
UAL143 - 7 2026-07-22
UAL142 United Airlines 7 2026-07-23
UAL263 - 6 2026-07-15
UAL2 - 6 2026-06-16
UAL760 United Airlines 5 2026-07-21
UAL262 - 5 2026-07-15
UAL187 - 5 2026-06-19
UAL842 - 4 2026-06-21

Recent flights last 50

DateFlightRouteTakeoffLandingDuration
2026-07-26 UAL178 KIX → GUM Jul 26, 12:45 UTCJul 26, 22:00 UTC9h 15m
2026-07-26 UAL177 GUM → KIX Jul 26, 00:20 UTCJul 26, 10:15 UTC9h 56m
2026-07-25 UAL26 LHR → DEN Jul 25, 10:50 UTCJul 25, 20:01 UTC9h 11m
2026-07-25 UAL26 LHR → DEN Jul 25, 10:55 UTCJul 25, 20:05 UTC9h 10m
2026-07-24 UAL27 DEN → LHR Jul 24, 23:55 UTCJul 25, 08:25 UTC8h 30m
2026-07-24 UAL181 FRA → DEN Jul 24, 09:35 UTCJul 24, 19:25 UTC9h 50m
2026-07-23 UAL182 DEN → FRA Jul 23, 22:25 UTCJul 24, 07:00 UTC8h 35m
2026-07-23 UAL142 NRT → DEN Jul 23, 07:50 UTCJul 23, 18:00 UTC10h 10m
2026-07-22 UAL143 DEN → NRT Jul 22, 18:10 UTCJul 23, 05:10 UTC11h 0m
2026-07-22 UAL143 DEN → NRT Jul 22, 18:04 UTCJul 23, 05:10 UTC11h 6m
2026-07-21 UAL761 - Jul 21, 16:00 UTCJul 22, 01:45 UTC9h 45m
2026-07-21 UAL760 DEN → MUC Jul 21, 04:15 UTCJul 21, 13:17 UTC9h 2m
2026-07-21 UAL760 DEN → MUC Jul 21, 04:05 UTCJul 21, 13:30 UTC9h 25m
2026-07-20 UAL178 - Jul 20, 15:10 UTCJul 20, 18:10 UTC3h 0m
2026-07-20 UAL178 FCO → DEN Jul 20, 14:27 UTCJul 21, 01:54 UTC11h 27m
2026-07-20 UAL177 GUM → KIX Jul 20, 02:10 UTCJul 20, 11:50 UTC9h 40m
2026-07-19 UAL181 FRA → DEN Jul 19, 09:41 UTCJul 19, 19:12 UTC9h 31m
2026-07-19 UAL181 FRA → DEN Jul 19, 09:45 UTCJul 19, 19:15 UTC9h 30m
2026-07-18 UAL182 - Jul 18, 22:25 UTCJul 19, 07:15 UTC8h 50m
2026-07-18 UAL142 - Jul 18, 07:55 UTCJul 18, 18:25 UTC10h 30m
2026-07-17 UAL143 DEN → NRT Jul 17, 18:04 UTCJul 18, 04:48 UTC10h 44m
2026-07-17 UAL143 DEN → NRT Jul 17, 18:05 UTCJul 18, 04:50 UTC10h 46m
2026-07-16 UAL761 - Jul 16, 16:05 UTCJul 17, 01:45 UTC9h 40m
2026-07-16 UAL760 - Jul 16, 04:45 UTCJul 16, 13:49 UTC9h 5m
2026-07-15 UAL263 - Jul 15, 15:50 UTCJul 15, 16:00 UTC10m
2026-07-15 UAL263 LHR → DEN Jul 15, 15:24 UTCJul 16, 00:35 UTC9h 11m
2026-07-15 UAL262 DEN → LHR Jul 15, 03:50 UTCJul 15, 12:06 UTC8h 16m
2026-07-15 UAL262 DEN → LHR Jul 15, 03:50 UTCJul 15, 12:20 UTC8h 30m
2026-07-14 UAL178 - Jul 14, 12:50 UTCJul 14, 23:15 UTC10h 24m
2026-07-14 UAL177 DEN → FCO Jul 14, 00:20 UTCJul 14, 10:25 UTC10h 5m
2026-07-13 UAL26 - Jul 13, 11:05 UTCJul 13, 19:50 UTC8h 45m
2026-07-13 UAL26 LHR → DEN Jul 13, 10:50 UTCJul 13, 19:50 UTC9h 0m
2026-07-12 UAL27 DEN → LHR Jul 12, 23:50 UTCJul 13, 08:25 UTC8h 35m
2026-07-12 UAL181 FRA → DEN Jul 12, 09:45 UTCJul 12, 19:15 UTC9h 30m
2026-07-11 UAL182 DEN → FRA Jul 11, 22:15 UTCJul 12, 07:10 UTC8h 55m
2026-07-11 UAL181 - Jul 11, 09:35 UTCJul 11, 19:20 UTC9h 45m
2026-07-11 UAL181 FRA → DEN Jul 11, 09:41 UTCJul 11, 19:17 UTC9h 36m
2026-07-10 UAL182 - Jul 10, 22:10 UTCJul 11, 07:05 UTC8h 55m
2026-07-10 UAL142 - Jul 10, 08:35 UTCJul 10, 19:20 UTC10h 45m
2026-07-09 UAL143 DEN → NRT Jul 9, 18:04 UTCJul 10, 05:05 UTC11h 1m
2026-07-09 UAL143 - Jul 9, 17:55 UTCJul 10, 00:00 UTC6h 5m
2026-07-08 UAL761 - Jul 8, 14:40 UTCJul 9, 01:00 UTC10h 20m
2026-07-08 UAL760 - Jul 8, 03:00 UTCJul 8, 12:20 UTC9h 20m
2026-07-07 UAL178 KIX → GUM Jul 7, 23:25 UTCJul 8, 00:00 UTC35m
2026-07-07 UAL178 KIX → GUM Jul 7, 12:50 UTCJul 7, 15:25 UTC2h 35m
2026-07-07 UAL178 KIX → GUM Jul 7, 12:47 UTCJul 7, 23:10 UTC10h 23m
2026-07-07 UAL177 DEN → FCO Jul 7, 00:08 UTCJul 7, 10:37 UTC10h 29m
2026-07-07 UAL177 DEN → FCO Jul 7, 00:40 UTCJul 7, 10:40 UTC10h 0m
2026-07-06 UAL26 - Jul 6, 10:50 UTCJul 6, 20:00 UTC9h 10m
2026-07-06 UAL27 DEN → LHR Jul 6, 00:00 UTCJul 6, 08:25 UTC8h 25m

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 N24974 page for operator, model, and routing details .

Mode-S A254D8 frequently asked

What is Mode-S code A254D8?
A254D8 is an ICAO 24-bit transponder address. Allocated to United States. Assigned to N24974.
Where is Mode-S A254D8 registered?
Mode-S code A254D8 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 A254D8 broadcasting right now?
No active broadcast right now. Last signal was Jul 26, 22:00 UTC.
Hex, octal, and decimal Mode-S codes: what's the difference?
The same 24-bit identifier expressed in different bases: hex A254D8, octal 50452330, decimal 10,638,552.
What flights does A254D8 operate?
Mode-S A254D8 has broadcast 20 distinct callsigns, including UAL820, UAL821, UAL26, UAL178, UAL27.