Apparatus

Try JFK, AAL1290, BAW, or N225AN.

sensors Mode-S transponder

A21633

ICAO 24-bit transponder address · allocated to United States

Currently assigned to N2331U · BOEING 777-300ER · operated by UNITED AIRLINES INC

Hex
A21633
Octal
50413063
Decimal
10,622,515
Country
US
Tail
N2331U
Type
B77W
No current signal · last broadcast Jul 26, 22:45 UTC
Flights observed
247
Distinct callsigns
20
Country
US
Last broadcast
Jul 26, 22:45 UTC

Last known position

Most recent position reported by Mode-S A21633.

Country allocation

The ICAO 24-bit address A21633 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
UAL838 - 13 2026-07-05
UAL989 United Airlines 11 2026-07-24
UAL951 United Airlines 11 2026-07-24
UAL878 - 11 2026-07-09
UAL871 - 11 2026-07-02
UAL809 - 11 2026-06-25
UAL43 United Airlines 11 2026-07-25
UAL869 - 10 2026-07-08
UAL988 - 9 2026-07-23
UAL872 - 9 2026-07-03
UAL190 - 9 2026-07-11
UAL950 United Airlines 8 2026-07-23
UAL858 - 8 2026-07-08
UAL837 United Airlines 8 2026-07-04
UAL810 - 8 2026-06-26
UAL42 United Airlines 8 2026-07-23
UAL862 - 7 2026-06-28
UAL79 United Airlines 7 2026-07-20
UAL78 - 7 2026-07-21
UAL857 - 6 2026-07-06

Recent flights last 50

DateFlightRouteTakeoffLandingDuration
2026-07-26 UAL40 EWR → FCO Jul 26, 21:50 UTCJul 26, 22:45 UTC55m
2026-07-26 UAL41 FCO → EWR Jul 26, 09:55 UTCJul 26, 11:55 UTC2h 0m
2026-07-26 UAL41 FCO → EWR Jul 26, 09:27 UTCJul 26, 18:24 UTC8h 57m
2026-07-26 UAL41 FCO → EWR Jul 26, 09:27 UTCJul 26, 18:21 UTC8h 54m
2026-07-25 UAL40 EWR → FCO Jul 25, 21:40 UTCJul 26, 05:20 UTC7h 40m
2026-07-25 UAL43 OGG → EWR Jul 25, 09:40 UTCJul 25, 17:25 UTC7h 45m
2026-07-24 UAL989 IAD → FRA Jul 24, 22:13 UTCJul 25, 05:18 UTC7h 5m
2026-07-24 UAL989 IAD → FRA Jul 24, 22:35 UTCJul 25, 04:45 UTC6h 10m
2026-07-24 UAL951 BRU → IAD Jul 24, 10:15 UTCJul 24, 17:50 UTC7h 35m
2026-07-23 UAL950 IAD → BRU Jul 23, 22:50 UTCJul 24, 05:25 UTC6h 35m
2026-07-23 UAL988 - Jul 23, 10:40 UTCJul 23, 18:45 UTC8h 5m
2026-07-23 UAL42 OGG → EWR Jul 23, 00:00 UTCJul 23, 00:45 UTC45m
2026-07-23 UAL42 OGG → EWR Jul 23, 00:00 UTCJul 23, 06:47 UTC6h 47m
2026-07-22 UAL905 LHR → EWR Jul 22, 10:20 UTCJul 22, 16:25 UTC6h 5m
2026-07-22 UAL14 EWR → LHR Jul 22, 00:38 UTCJul 22, 06:38 UTC6h 0m
2026-07-22 UAL14 EWR → LHR Jul 22, 00:20 UTCJul 22, 05:25 UTC5h 5m
2026-07-21 UAL78 - Jul 21, 21:10 UTCJul 21, 21:15 UTC5m
2026-07-21 UAL78 - Jul 21, 09:05 UTCJul 21, 15:30 UTC6h 25m
2026-07-21 UAL78 NRT → EWR Jul 21, 09:06 UTCJul 21, 20:51 UTC11h 45m
2026-07-20 UAL79 EWR → NRT Jul 20, 16:02 UTCJul 21, 06:14 UTC14h 12m
2026-07-20 UAL79 EWR → NRT Jul 20, 16:05 UTCJul 21, 06:25 UTC14h 20m
2026-07-20 UAL2416 LAS → SFO Jul 20, 07:35 UTCJul 20, 12:05 UTC4h 30m
2026-07-19 UAL1844 EWR → MIA Jul 19, 22:50 UTCJul 20, 04:10 UTC5h 20m
2026-07-19 UAL3043 - Jul 19, 16:50 UTCJul 19, 19:25 UTC2h 35m
2026-07-18 UAL435 SFO → ORD Jul 18, 16:10 UTCJul 18, 20:55 UTC4h 45m
2026-07-17 UAL1844 EWR → MIA Jul 17, 22:35 UTCJul 18, 04:10 UTC5h 36m
2026-07-16 UAL43 - Jul 16, 09:55 UTCJul 16, 11:40 UTC1h 45m
2026-07-16 UAL43 FRA → EWR Jul 16, 10:00 UTCJul 16, 17:33 UTC7h 33m
2026-07-16 UAL43 FRA → EWR Jul 16, 10:00 UTCJul 16, 17:46 UTC7h 46m
2026-07-15 UAL989 IAD → FRA Jul 15, 22:05 UTCJul 16, 05:40 UTC7h 35m
2026-07-15 UAL989 IAD → FRA Jul 15, 21:43 UTCJul 16, 05:25 UTC7h 42m
2026-07-15 UAL951 BRU → IAD Jul 15, 11:20 UTCJul 15, 18:50 UTC7h 30m
2026-07-14 UAL950 IAD → BRU Jul 14, 22:23 UTCJul 15, 05:39 UTC7h 16m
2026-07-14 UAL950 IAD → BRU Jul 14, 22:30 UTCJul 15, 05:45 UTC7h 14m
2026-07-14 UAL988 - Jul 14, 10:45 UTCJul 14, 18:35 UTC7h 50m
2026-07-14 UAL42 EWR → FRA Jul 14, 00:30 UTCJul 14, 07:25 UTC6h 55m
2026-07-13 UAL78 - Jul 13, 08:45 UTCJul 13, 20:45 UTC12h 0m
2026-07-12 UAL79 EWR → NRT Jul 12, 16:02 UTCJul 13, 05:06 UTC13h 4m
2026-07-12 UAL79 - Jul 12, 15:55 UTCJul 13, 05:05 UTC13h 10m
2026-07-12 UAL2416 - Jul 12, 07:35 UTCJul 12, 12:10 UTC4h 35m
2026-07-11 UAL190 MNL → SFO Jul 11, 01:01 UTCJul 11, 13:40 UTC12h 39m
2026-07-11 UAL190 - Jul 11, 01:10 UTCJul 11, 13:50 UTC12h 40m
2026-07-10 UAL189 - Jul 10, 08:55 UTCJul 10, 22:25 UTC13h 30m
2026-07-09 UAL878 HKG → SFO Jul 9, 14:51 UTCJul 10, 02:55 UTC12h 4m
2026-07-09 UAL878 - Jul 9, 14:40 UTCJul 10, 03:00 UTC12h 20m
2026-07-08 UAL869 SFO → HKG Jul 8, 21:12 UTCJul 9, 10:39 UTC13h 27m
2026-07-08 UAL869 SFO → HKG Jul 8, 21:05 UTCJul 9, 10:35 UTC13h 30m
2026-07-08 UAL858 PVG → SFO Jul 8, 04:44 UTCJul 8, 15:22 UTC10h 38m
2026-07-07 UAL858 - Jul 7, 06:50 UTCJul 8, 06:45 UTC23h 55m
2026-07-06 UAL857 - Jul 6, 21:05 UTCJul 7, 08:15 UTC11h 10m

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 N2331U page for operator, model, and routing details .

Mode-S A21633 frequently asked

What is Mode-S code A21633?
A21633 is an ICAO 24-bit transponder address. Allocated to United States. Assigned to N2331U.
Where is Mode-S A21633 registered?
Mode-S code A21633 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 A21633 broadcasting right now?
No active broadcast right now. Last signal was Jul 26, 22:45 UTC.
Hex, octal, and decimal Mode-S codes: what's the difference?
The same 24-bit identifier expressed in different bases: hex A21633, octal 50413063, decimal 10,622,515.
What flights does A21633 operate?
Mode-S A21633 has broadcast 20 distinct callsigns, including UAL838, UAL989, UAL951, UAL878, UAL871.