Apparatus

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sensors Mode-S transponder

A2551D

ICAO 24-bit transponder address · allocated to United States

Currently assigned to N24993 · BOEING 787-9 Dreamliner · operated by UNITED AIRLINES INC

Hex
A2551D
Octal
50452435
Decimal
10,638,621
Country
US
Tail
N24993
Type
B789
No current signal · last broadcast Jul 26, 19:45 UTC
Flights observed
232
Distinct callsigns
20
Country
US
Last broadcast
Jul 26, 19:45 UTC

Last known position

Most recent position reported by Mode-S A2551D.

Country allocation

The ICAO 24-bit address A2551D 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
UAL27 - 17 2026-07-15
UAL26 - 16 2026-07-15
UAL263 - 15 2026-07-10
UAL761 - 14 2026-07-17
UAL142 - 13 2026-07-14
UAL143 - 12 2026-07-18
UAL760 - 11 2026-07-17
UAL181 - 11 2026-07-06
UAL178 - 11 2026-07-16
UAL82 United Airlines 10 2026-05-05
UAL262 - 10 2026-07-10
UAL182 United Airlines 10 2026-07-05
UAL177 - 10 2026-07-16
UAL83 United Airlines 8 2026-05-05
UAL863 United Airlines 4 2026-05-01
UAL153 - 4 2026-07-21
UAL870 United Airlines 3 2026-05-02
UAL79 United Airlines 3 2026-05-06
UAL63 United Airlines 3 2026-06-03
UAL62 United Airlines 3 2026-06-02

Recent flights last 50

DateFlightRouteTakeoffLandingDuration
2026-07-26 UAL6 NRT → IAH Jul 26, 08:20 UTCJul 26, 19:45 UTC11h 25m
2026-07-25 UAL32 LAX → NRT Jul 25, 18:35 UTCJul 26, 05:00 UTC10h 25m
2026-07-25 UAL32 LAX → NRT Jul 25, 18:15 UTCJul 26, 05:00 UTC10h 45m
2026-07-24 UAL353 SAN → EWR Jul 24, 22:55 UTCJul 25, 03:45 UTC4h 50m
2026-07-24 UAL2096 LAX → EWR Jul 24, 16:30 UTCJul 24, 21:00 UTC4h 30m
2026-07-23 UAL99 MEL → LAX Jul 23, 23:50 UTCJul 24, 13:25 UTC13h 35m
2026-07-23 UAL98 LAX → MEL Jul 23, 06:30 UTCJul 23, 21:35 UTC15h 5m
2026-07-22 UAL199 - Jul 22, 14:00 UTCJul 23, 01:10 UTC11h 10m
2026-07-21 UAL199 - Jul 21, 21:20 UTCJul 22, 15:30 UTC18h 10m
2026-07-21 UAL199 - Jul 21, 21:05 UTCJul 22, 15:30 UTC18h 25m
2026-07-21 UAL153 HKG → LAX Jul 21, 05:10 UTCJul 21, 18:25 UTC13h 15m
2026-07-21 UAL153 HKG → LAX Jul 21, 05:08 UTCJul 21, 18:17 UTC13h 9m
2026-07-21 UAL153 - Jul 21, 02:30 UTCJul 21, 02:50 UTC20m
2026-07-21 UAL153 HKG → LAX Jul 21, 00:19 UTCJul 21, 02:46 UTC2h 27m
2026-07-20 UAL152 - Jul 20, 13:05 UTCJul 20, 13:20 UTC15m
2026-07-20 UAL152 LAX → HKG Jul 20, 12:49 UTCJul 20, 15:03 UTC2h 14m
2026-07-19 UAL152 - Jul 19, 20:10 UTCJul 20, 09:50 UTC13h 40m
2026-07-19 UAL33 NRT → LAX Jul 19, 08:10 UTCJul 19, 17:50 UTC9h 40m
2026-07-19 UAL33 NRT → LAX Jul 19, 08:05 UTCJul 19, 17:44 UTC9h 39m
2026-07-18 UAL143 - Jul 18, 18:30 UTCJul 19, 05:30 UTC11h 0m
2026-07-17 UAL761 - Jul 17, 14:39 UTCJul 17, 16:59 UTC2h 20m
2026-07-17 UAL761 MUC → DEN Jul 17, 14:31 UTCJul 18, 00:33 UTC10h 2m
2026-07-17 UAL761 MUC → DEN Jul 17, 14:31 UTCJul 18, 00:33 UTC10h 2m
2026-07-17 UAL760 DEN → MUC Jul 17, 02:45 UTCJul 17, 12:13 UTC9h 28m
2026-07-17 UAL760 DEN → MUC Jul 17, 02:39 UTCJul 17, 12:10 UTC9h 30m
2026-07-16 UAL178 - Jul 16, 12:44 UTCJul 16, 23:40 UTC10h 55m
2026-07-16 UAL177 DEN → FCO Jul 16, 00:10 UTCJul 16, 10:04 UTC9h 55m
2026-07-15 UAL26 - Jul 15, 11:00 UTCJul 15, 19:45 UTC8h 45m
2026-07-15 UAL27 - Jul 15, 00:00 UTCJul 15, 08:40 UTC8h 40m
2026-07-14 UAL142 - Jul 14, 08:05 UTCJul 14, 18:10 UTC10h 5m
2026-07-14 UAL142 NRT → DEN Jul 14, 07:55 UTCJul 14, 18:09 UTC10h 14m
2026-07-13 UAL143 DEN → NRT Jul 13, 18:04 UTCJul 14, 05:19 UTC11h 15m
2026-07-13 UAL143 DEN → NRT Jul 13, 18:05 UTCJul 14, 05:25 UTC11h 20m
2026-07-12 UAL761 - Jul 12, 14:30 UTCJul 12, 15:15 UTC45m
2026-07-12 UAL761 MUC → DEN Jul 12, 14:31 UTCJul 13, 00:16 UTC9h 45m
2026-07-12 UAL761 MUC → DEN Jul 12, 14:31 UTCJul 13, 00:18 UTC9h 47m
2026-07-12 UAL760 DEN → MUC Jul 12, 02:45 UTCJul 12, 12:00 UTC9h 15m
2026-07-12 UAL760 - Jul 12, 02:40 UTCJul 12, 03:15 UTC35m
2026-07-11 UAL761 - Jul 11, 14:35 UTCJul 12, 00:30 UTC9h 55m
2026-07-11 UAL760 DEN → MUC Jul 11, 03:10 UTCJul 11, 12:20 UTC9h 10m
2026-07-10 UAL263 LHR → DEN Jul 10, 14:20 UTCJul 10, 23:10 UTC8h 51m
2026-07-10 UAL262 DEN → LHR Jul 10, 02:45 UTCJul 10, 11:20 UTC8h 35m
2026-07-09 UAL178 - Jul 9, 12:55 UTCJul 9, 23:40 UTC10h 45m
2026-07-09 UAL178 FCO → DEN Jul 9, 12:47 UTCJul 9, 23:39 UTC10h 52m
2026-07-09 UAL177 DEN → FCO Jul 9, 00:20 UTCJul 9, 10:15 UTC9h 55m
2026-07-08 UAL26 - Jul 8, 11:00 UTCJul 8, 19:50 UTC8h 50m
2026-07-08 UAL27 DEN → LHR Jul 8, 00:15 UTCJul 8, 08:50 UTC8h 35m
2026-07-07 UAL26 - Jul 7, 11:25 UTCJul 7, 20:25 UTC9h 0m
2026-07-07 UAL27 DEN → LHR Jul 7, 00:40 UTCJul 7, 09:10 UTC8h 30m
2026-07-06 UAL181 FRA → DEN Jul 6, 09:45 UTCJul 6, 19:30 UTC9h 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 N24993 page for operator, model, and routing details .

Mode-S A2551D frequently asked

What is Mode-S code A2551D?
A2551D is an ICAO 24-bit transponder address. Allocated to United States. Assigned to N24993.
Where is Mode-S A2551D registered?
Mode-S code A2551D 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 A2551D broadcasting right now?
No active broadcast right now. Last signal was Jul 26, 19:45 UTC.
Hex, octal, and decimal Mode-S codes: what's the difference?
The same 24-bit identifier expressed in different bases: hex A2551D, octal 50452435, decimal 10,638,621.
What flights does A2551D operate?
Mode-S A2551D has broadcast 20 distinct callsigns, including UAL27, UAL26, UAL263, UAL761, UAL142.