Apparatus

Try JFK, AAL1290, BAW, or N225AN.

sensors Mode-S transponder

A2551A

ICAO 24-bit transponder address · allocated to United States

Currently assigned to N24990 · BOEING 787-9 Dreamliner · operated by UNITED AIRLINES INC

Hex
A2551A
Octal
50452432
Decimal
10,638,618
Country
US
Tail
N24990
Type
B789
Broadcasting now · callsign UAL3905 · 41,000 ft
Flights observed
206
Distinct callsigns
20
Country
US
Last broadcast
45m ago

Current position

A2551A is currently broadcasting. Map zoomed to live position.

Country allocation

The ICAO 24-bit address A2551A 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
UAL198 United Airlines 12 2026-05-30
UAL820 United Airlines 11 2026-05-13
UAL153 United Airlines 11 2026-05-17
UAL821 United Airlines 9 2026-05-13
UAL152 United Airlines 9 2026-05-16
UAL199 United Airlines 8 2026-05-31
UAL123 - 8 2026-07-05
UAL839 United Airlines 7 2026-05-14
UAL713 - 7 2026-07-10
UAL61 - 7 2026-07-07
UAL187 - 7 2026-07-03
UAL842 United Airlines 6 2026-06-05
UAL60 - 5 2026-07-06
UAL188 United Airlines 5 2026-07-03
UAL949 - 4 2026-07-09
UAL892 - 4 2026-07-08
UAL2692 - 4 2026-07-13
UAL2480 United Airlines 4 2026-06-08
UAL1227 - 4 2026-07-05
UAL122 - 4 2026-07-04

Recent flights last 50

DateFlightRouteTakeoffLandingDuration
2026-07-14 UAL3905 - Jul 14, 03:30 UTCJul 14, 10:05 UTC6h 35m
2026-07-13 UAL1855 - Jul 13, 20:40 UTCJul 14, 01:35 UTC4h 55m
2026-07-13 UAL2692 EWR → LAX Jul 13, 13:49 UTCJul 13, 17:58 UTC4h 9m
2026-07-13 UAL2692 - Jul 13, 13:25 UTCJul 13, 16:30 UTC3h 5m
2026-07-12 UAL1855 - Jul 12, 21:10 UTCJul 13, 01:50 UTC4h 40m
2026-07-12 UAL2692 - Jul 12, 13:45 UTCJul 12, 18:25 UTC4h 40m
2026-07-11 UAL83 - Jul 11, 18:35 UTCJul 12, 10:05 UTC15h 30m
2026-07-11 UAL82 - Jul 11, 02:15 UTCJul 11, 16:00 UTC13h 45m
2026-07-10 UAL713 SFO → EWR Jul 10, 17:50 UTCJul 10, 22:35 UTC4h 45m
2026-07-10 UAL713 SFO → EWR Jul 10, 17:35 UTCJul 10, 22:45 UTC5h 10m
2026-07-09 UAL949 - Jul 9, 12:45 UTCJul 9, 23:05 UTC10h 20m
2026-07-09 UAL948 SFO → LHR Jul 9, 00:25 UTCJul 9, 10:15 UTC9h 50m
2026-07-08 UAL892 ICN → SFO Jul 8, 08:05 UTCJul 8, 18:20 UTC10h 15m
2026-07-07 UAL893 SFO → ICN Jul 7, 18:20 UTCJul 8, 06:00 UTC11h 40m
2026-07-07 UAL61 MEL → SFO Jul 7, 01:45 UTCJul 7, 15:00 UTC13h 15m
2026-07-06 UAL60 - Jul 6, 07:20 UTCJul 6, 22:25 UTC15h 5m
2026-07-05 UAL1227 - Jul 5, 17:55 UTCJul 5, 23:05 UTC5h 10m
2026-07-05 UAL123 - Jul 5, 07:00 UTCJul 5, 14:05 UTC7h 5m
2026-07-05 UAL123 LHR → EWR Jul 5, 07:02 UTCJul 5, 14:14 UTC7h 12m
2026-07-04 UAL122 EWR → LHR Jul 4, 14:00 UTCJul 4, 20:05 UTC6h 5m
2026-07-03 UAL187 - Jul 3, 20:05 UTCJul 4, 11:15 UTC15h 10m
2026-07-03 UAL187 JNB → EWR Jul 3, 20:19 UTCJul 4, 11:11 UTC14h 52m
2026-07-03 UAL188 EWR → JNB Jul 3, 01:55 UTCJul 3, 16:05 UTC14h 10m
2026-07-03 UAL188 EWR → JNB Jul 3, 01:54 UTCJul 3, 16:00 UTC14h 6m
2026-07-02 UAL713 SFO → EWR Jul 2, 17:50 UTCJul 2, 22:30 UTC4h 40m
2026-07-02 UAL713 SFO → EWR Jul 2, 17:55 UTCJul 2, 22:36 UTC4h 41m
2026-07-02 UAL61 - Jul 2, 01:15 UTCJul 2, 15:00 UTC13h 45m
2026-07-01 UAL60 SFO → MEL Jul 1, 07:10 UTCJul 1, 22:30 UTC15h 20m
2026-06-30 UAL949 - Jun 30, 13:50 UTCJun 30, 19:55 UTC6h 5m
2026-06-30 UAL949 LHR → SFO Jun 30, 13:50 UTCJun 30, 23:42 UTC9h 52m
2026-06-30 UAL949 LHR → SFO Jun 30, 13:50 UTCJun 30, 23:42 UTC9h 52m
2026-06-30 UAL948 SFO → LHR Jun 30, 01:45 UTCJun 30, 11:40 UTC9h 55m
2026-06-29 UAL1227 - Jun 29, 18:19 UTCJun 29, 23:25 UTC5h 5m
2026-06-29 UAL123 - Jun 29, 06:50 UTCJun 29, 08:14 UTC1h 25m
2026-06-29 UAL123 LHR → EWR Jun 29, 06:52 UTCJun 29, 13:47 UTC6h 55m
2026-06-29 UAL123 LHR → EWR Jun 29, 06:52 UTCJun 29, 13:49 UTC6h 57m
2026-06-28 UAL122 EWR → LHR Jun 28, 13:45 UTCJun 28, 19:44 UTC6h 0m
2026-06-27 UAL2222 - Jun 27, 17:59 UTCJun 28, 08:39 UTC14h 40m
2026-06-27 UAL1122 - Jun 27, 00:50 UTCJun 27, 14:45 UTC13h 55m
2026-06-26 UAL187 - Jun 26, 11:34 UTCJun 26, 11:40 UTC5m
2026-06-25 UAL187 - Jun 25, 20:19 UTCJun 25, 23:24 UTC3h 5m
2026-06-25 UAL187 JNB → EWR Jun 25, 20:19 UTCJun 26, 11:19 UTC15h 0m
2026-06-25 UAL188 EWR → JNB Jun 25, 01:50 UTCJun 25, 15:59 UTC14h 10m
2026-06-24 UAL713 - Jun 24, 17:50 UTCJun 24, 22:25 UTC4h 35m
2026-06-24 UAL61 MEL → SFO Jun 24, 01:29 UTCJun 24, 14:29 UTC13h 0m
2026-06-24 UAL61 MEL → SFO Jun 24, 01:24 UTCJun 24, 14:24 UTC13h 0m
2026-06-23 UAL60 SFO → MEL Jun 23, 07:15 UTCJun 23, 22:44 UTC15h 30m
2026-06-22 UAL1757 - Jun 22, 23:29 UTCJun 23, 04:39 UTC5h 10m
2026-06-22 UAL1757 IAD → SFO Jun 22, 22:44 UTCJun 23, 04:26 UTC5h 42m
2026-06-21 UAL2274 SFO → IAD Jun 21, 20:05 UTCJun 22, 00:24 UTC4h 20m

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 N24990 page for operator, model, and routing details .

Mode-S A2551A frequently asked

What is Mode-S code A2551A?
A2551A is an ICAO 24-bit transponder address. Allocated to United States. Assigned to N24990.
Where is Mode-S A2551A registered?
Mode-S code A2551A 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 A2551A broadcasting right now?
Yes. Mode-S A2551A is currently airborne.
Hex, octal, and decimal Mode-S codes: what's the difference?
The same 24-bit identifier expressed in different bases: hex A2551A, octal 50452432, decimal 10,638,618.
What flights does A2551A operate?
Mode-S A2551A has broadcast 20 distinct callsigns, including UAL198, UAL820, UAL153, UAL821, UAL152.