Apparatus

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sensors Mode-S transponder

A81000

ICAO 24-bit transponder address · allocated to United States

Currently assigned to N61881 · BOEING 737-900 · operated by UNITED AIRLINES INC

Hex
A81000
Octal
52010000
Decimal
11,014,144
Country
US
Tail
N61881
Type
B739
No current signal · last broadcast Jul 26, 22:00 UTC
Flights observed
414
Distinct callsigns
20
Country
US
Last broadcast
Jul 26, 22:00 UTC

Last known position

Most recent position reported by Mode-S A81000.

Country allocation

The ICAO 24-bit address A81000 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
UAL2737 United Airlines 6 2026-06-04
UAL2277 - 6 2026-06-29
UAL1617 - 5 2026-07-13
UAL495 United Airlines 4 2026-05-12
UAL431 United Airlines 4 2026-04-27
UAL2665 - 4 2026-07-13
UAL2376 United Airlines 4 2026-04-18
UAL2095 United Airlines 4 2026-05-30
UAL2014 United Airlines 4 2026-07-21
UAL1761 - 4 2026-07-15
UAL1449 - 4 2026-07-03
UAL1014 United Airlines 4 2026-06-20
UAL774 United Airlines 3 2026-05-17
UAL424 - 3 2026-07-01
UAL279 - 3 2026-07-14
UAL2741 United Airlines 3 2026-05-18
UAL2736 United Airlines 3 2026-06-04
UAL2671 United Airlines 3 2026-04-18
UAL2645 United Airlines 3 2026-07-03
UAL2640 - 3 2026-07-08

Recent flights last 50

DateFlightRouteTakeoffLandingDuration
2026-07-26 UAL1545 SFO → LAX Jul 26, 19:40 UTCJul 26, 22:00 UTC2h 20m
2026-07-26 UAL2067 IAH → LGA Jul 26, 15:45 UTCJul 26, 18:20 UTC2h 35m
2026-07-26 UAL715 ORD → PBI Jul 26, 11:35 UTCJul 26, 13:45 UTC2h 10m
2026-07-25 UAL2172 IAH → PHL Jul 25, 20:46 UTCJul 25, 21:23 UTC37m
2026-07-25 UAL2172 IAH → PHL Jul 25, 20:30 UTCJul 25, 21:25 UTC55m
2026-07-25 UAL1856 DEN → SFO Jul 25, 16:10 UTCJul 25, 17:50 UTC1h 40m
2026-07-25 UAL1695 EWR → MCO Jul 25, 12:40 UTCJul 25, 14:35 UTC1h 55m
2026-07-24 UAL414 EWR → SFO Jul 24, 22:40 UTCJul 25, 00:05 UTC1h 25m
2026-07-24 UAL1587 RSW → EWR Jul 24, 17:10 UTCJul 24, 20:25 UTC3h 15m
2026-07-24 UAL1279 EWR → SFO Jul 24, 12:25 UTCJul 24, 15:15 UTC2h 50m
2026-07-24 UAL1291 EWR → BNA Jul 24, 01:31 UTCJul 24, 02:45 UTC1h 14m
2026-07-24 UAL1291 EWR → BNA Jul 24, 01:25 UTCJul 24, 02:45 UTC1h 20m
2026-07-23 UAL716 CHS → DEN Jul 23, 22:15 UTCJul 23, 23:45 UTC1h 30m
2026-07-21 UAL1236 EWR → PHX Jul 21, 23:15 UTCJul 22, 01:45 UTC2h 30m
2026-07-21 UAL1767 DEN → DCA Jul 21, 18:30 UTCJul 21, 20:55 UTC2h 25m
2026-07-21 UAL1782 BOI → DEN Jul 21, 12:50 UTCJul 21, 14:20 UTC1h 30m
2026-07-21 UAL2014 DEN → SDF Jul 21, 01:55 UTCJul 21, 03:20 UTC1h 25m
2026-07-21 UAL2014 DEN → SDF Jul 21, 01:48 UTCJul 21, 03:16 UTC1h 28m
2026-07-20 UAL2012 PTY → EWR Jul 20, 20:40 UTCJul 20, 23:55 UTC3h 15m
2026-07-20 UAL1362 DEN → BWI Jul 20, 16:10 UTCJul 20, 19:05 UTC2h 55m
2026-07-20 UAL2185 MFR → DEN Jul 20, 12:10 UTCJul 20, 14:10 UTC2h 0m
2026-07-20 UAL663 DEN → ABQ Jul 20, 02:21 UTCJul 20, 04:26 UTC2h 5m
2026-07-20 UAL663 DEN → ABQ Jul 20, 02:20 UTCJul 20, 04:30 UTC2h 10m
2026-07-19 UAL2288 - Jul 19, 20:45 UTCJul 19, 23:55 UTC3h 10m
2026-07-19 UAL2269 DEN → RDU Jul 19, 16:20 UTCJul 19, 19:10 UTC2h 50m
2026-07-19 UAL1782 BOI → DEN Jul 19, 12:40 UTCJul 19, 14:00 UTC1h 20m
2026-07-19 UAL1782 BOI → DEN Jul 19, 12:49 UTCJul 19, 14:10 UTC1h 21m
2026-07-19 UAL2014 DEN → SDF Jul 19, 02:20 UTCJul 19, 03:45 UTC1h 25m
2026-07-19 UAL2014 DEN → SDF Jul 19, 02:05 UTCJul 19, 03:45 UTC1h 40m
2026-07-18 UAL1781 - Jul 18, 22:50 UTCJul 19, 00:10 UTC1h 20m
2026-07-18 UAL1311 EWR → CLT Jul 18, 19:50 UTCJul 18, 21:15 UTC1h 25m
2026-07-18 UAL2476 SAN → DEN Jul 18, 16:05 UTCJul 18, 18:05 UTC2h 0m
2026-07-18 UAL1343 SFO → SAN Jul 18, 03:45 UTCJul 18, 04:55 UTC1h 10m
2026-07-18 UAL2117 SAN → SFO Jul 18, 00:15 UTCJul 18, 01:20 UTC1h 5m
2026-07-17 UAL1302 DEN → SAN Jul 17, 19:55 UTCJul 17, 21:55 UTC2h 0m
2026-07-17 UAL597 EWR → LAS Jul 17, 16:40 UTCJul 17, 18:10 UTC1h 30m
2026-07-17 UAL1729 DEN → PHX Jul 17, 01:55 UTCJul 17, 03:25 UTC1h 30m
2026-07-17 UAL1729 LGA → DEN Jul 17, 01:52 UTCJul 17, 03:16 UTC1h 24m
2026-07-16 UAL2288 - Jul 16, 21:10 UTCJul 17, 00:10 UTC3h 0m
2026-07-16 UAL2269 DEN → RDU Jul 16, 16:44 UTCJul 16, 19:40 UTC2h 55m
2026-07-16 UAL1232 - Jul 16, 13:34 UTCJul 16, 14:35 UTC1h 0m
2026-07-16 UAL2769 DEN → SLC Jul 16, 01:45 UTCJul 16, 02:45 UTC1h 0m
2026-07-15 UAL395 IAD → DEN Jul 15, 20:55 UTCJul 15, 23:45 UTC2h 50m
2026-07-15 UAL2497 MSY → IAD Jul 15, 17:25 UTCJul 15, 19:30 UTC2h 5m
2026-07-15 UAL1761 ORD → MSY Jul 15, 02:20 UTCJul 15, 04:05 UTC1h 45m
2026-07-14 UAL403 - Jul 14, 20:35 UTCJul 14, 23:15 UTC2h 39m
2026-07-14 UAL279 ORD → FLL Jul 14, 16:30 UTCJul 14, 19:05 UTC2h 35m
2026-07-14 UAL2287 - Jul 14, 13:05 UTCJul 14, 14:05 UTC1h 0m
2026-07-14 UAL1325 ORD → DSM Jul 14, 02:00 UTCJul 14, 02:45 UTC45m
2026-07-13 UAL433 - Jul 13, 20:25 UTCJul 13, 22:00 UTC1h 35m

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 N61881 page for operator, model, and routing details .

Mode-S A81000 frequently asked

What is Mode-S code A81000?
A81000 is an ICAO 24-bit transponder address. Allocated to United States. Assigned to N61881.
Where is Mode-S A81000 registered?
Mode-S code A81000 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 A81000 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 A81000, octal 52010000, decimal 11,014,144.
What flights does A81000 operate?
Mode-S A81000 has broadcast 20 distinct callsigns, including UAL2737, UAL2277, UAL1617, UAL495, UAL431.