Apparatus

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sensors Mode-S transponder

A1BFF9

ICAO 24-bit transponder address · allocated to United States

Currently assigned to N21129 · EMBRAER ERJ-145XR · operated by UNITED AIRLINES INC

Hex
A1BFF9
Octal
50337771
Decimal
10,600,441
Country
US
Tail
N21129
Type
E45X
No current signal · last broadcast 12h ago
Flights observed
542
Distinct callsigns
20
Country
US
Last broadcast
12h ago

Last known position

Most recent position reported by Mode-S A1BFF9.

Country allocation

The ICAO 24-bit address A1BFF9 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
UCA4917 - 8 2026-06-22
UCA4996 - 6 2026-07-12
UCA4911 - 6 2026-07-12
UCA4830 - 6 2026-07-11
UCA4340 CommutAir 6 2026-05-29
UCA4297 CommutAir 6 2026-05-10
UCA4241 CommutAir 6 2026-07-07
UCA4226 - 6 2026-07-11
UCA4977 - 5 2026-06-28
UCA4938 - 5 2026-07-04
UCA4919 CommutAir 5 2026-05-11
UCA4853 - 5 2026-06-29
UCA4812 - 5 2026-07-03
UCA4330 - 5 2026-06-26
UCA4318 - 5 2026-06-23
UCA4250 CommutAir 5 2026-06-03
UCA4235 CommutAir 5 2026-06-06
UCA4229 - 5 2026-06-30
UCA4963 - 4 2026-07-06
UCA4950 CommutAir 4 2026-06-10

Recent flights last 50

DateFlightRouteTakeoffLandingDuration
2026-07-13 UCA4282 - Jul 13, 14:40 UTCJul 13, 15:30 UTC50m
2026-07-13 UCA4334 - Jul 13, 12:45 UTCJul 13, 13:30 UTC45m
2026-07-12 UCA4996 - Jul 12, 22:40 UTCJul 13, 00:05 UTC1h 25m
2026-07-12 UCA4911 - Jul 12, 19:50 UTCJul 12, 21:10 UTC1h 20m
2026-07-12 UCA4329 - Jul 12, 17:20 UTCJul 12, 18:15 UTC55m
2026-07-12 UCA4329 BRO → IAH Jul 12, 17:28 UTCJul 12, 18:19 UTC51m
2026-07-12 UCA4813 IAH → BRO Jul 12, 15:22 UTCJul 12, 15:55 UTC33m
2026-07-12 UCA4813 - Jul 12, 15:05 UTCJul 12, 15:50 UTC45m
2026-07-12 UCA4346 - Jul 12, 12:40 UTCJul 12, 13:35 UTC55m
2026-07-12 UCA4832 - Jul 12, 01:10 UTCJul 12, 01:50 UTC40m
2026-07-11 UCA4377 - Jul 11, 23:10 UTCJul 12, 00:10 UTC1h 0m
2026-07-11 UCA4377 CRP → IAH Jul 11, 22:38 UTCJul 12, 00:09 UTC1h 31m
2026-07-11 UCA4825 - Jul 11, 20:20 UTCJul 11, 21:00 UTC40m
2026-07-11 UCA4830 - Jul 11, 17:40 UTCJul 11, 19:10 UTC1h 30m
2026-07-11 UCA4830 LIT → IAH Jul 11, 17:33 UTCJul 11, 18:49 UTC1h 16m
2026-07-11 UCA4371 - Jul 11, 15:10 UTCJul 11, 15:50 UTC40m
2026-07-11 UCA4226 - Jul 11, 12:40 UTCJul 11, 13:30 UTC50m
2026-07-11 UCA4892 - Jul 11, 03:05 UTCJul 11, 04:01 UTC55m
2026-07-11 UCA4892 IAH → LRD Jul 11, 03:07 UTCJul 11, 04:09 UTC1h 2m
2026-07-11 UCA4228 - Jul 11, 00:00 UTCJul 11, 01:25 UTC1h 25m
2026-07-10 UCA4256 - Jul 10, 21:35 UTCJul 10, 23:05 UTC1h 30m
2026-07-10 UCA4934 - Jul 10, 19:30 UTCJul 10, 19:55 UTC25m
2026-07-10 UCA4934 LCH → IAH Jul 10, 19:27 UTCJul 10, 19:43 UTC16m
2026-07-10 UCA4921 - Jul 10, 17:45 UTCJul 10, 18:00 UTC15m
2026-07-10 UCA4921 IAH → LCH Jul 10, 17:47 UTCJul 10, 18:16 UTC29m
2026-07-10 UCA4376 - Jul 10, 14:50 UTCJul 10, 15:45 UTC55m
2026-07-10 UCA4355 - Jul 10, 12:50 UTCJul 10, 13:40 UTC50m
2026-07-10 UCA4355 IAH → MFE Jul 10, 12:53 UTCJul 10, 13:46 UTC53m
2026-07-09 UCA4111 - Jul 9, 23:20 UTCJul 10, 01:50 UTC2h 30m
2026-07-09 UCA4110 - Jul 9, 19:05 UTCJul 9, 21:30 UTC2h 25m
2026-07-09 UCA4110 IAH → MOT Jul 9, 19:08 UTCJul 9, 21:53 UTC2h 45m
2026-07-09 UCA4271 - Jul 9, 14:30 UTCJul 9, 15:20 UTC50m
2026-07-09 UCA4309 - Jul 9, 01:40 UTCJul 9, 02:20 UTC40m
2026-07-08 UCA4984 - Jul 8, 23:30 UTCJul 8, 23:45 UTC15m
2026-07-08 UCA4375 - Jul 8, 22:05 UTCJul 8, 22:20 UTC15m
2026-07-08 UCA4980 - Jul 8, 19:25 UTCJul 8, 20:30 UTC1h 5m
2026-07-08 UCA4287 - Jul 8, 17:30 UTCJul 8, 18:10 UTC40m
2026-07-08 UCA4287 IAH → HRL Jul 8, 17:33 UTCJul 8, 18:13 UTC40m
2026-07-08 UCA4989 MOB → IAH Jul 8, 14:10 UTCJul 8, 15:15 UTC1h 5m
2026-07-07 UCA4295 IAD → MOB Jul 7, 23:15 UTCJul 8, 01:10 UTC1h 55m
2026-07-07 UCA4824 - Jul 7, 19:15 UTCJul 7, 20:35 UTC1h 20m
2026-07-07 UCA4824 DAY → IAD Jul 7, 19:07 UTCJul 7, 20:26 UTC1h 19m
2026-07-07 UCA4241 BTV → IAD Jul 7, 17:10 UTCJul 7, 18:15 UTC1h 5m
2026-07-07 UCA4860 - Jul 7, 10:15 UTCJul 7, 11:15 UTC1h 0m
2026-07-07 UCA4856 - Jul 7, 05:25 UTCJul 7, 06:10 UTC45m
2026-07-07 UCA4313 - Jul 7, 00:40 UTCJul 7, 01:40 UTC1h 0m
2026-07-06 UCA4963 - Jul 6, 22:50 UTCJul 6, 23:50 UTC1h 0m
2026-07-06 UCA4963 IAD → GSP Jul 6, 21:43 UTCJul 6, 23:50 UTC2h 7m
2026-07-06 UCA4328 - Jul 6, 19:10 UTCJul 6, 19:30 UTC20m
2026-07-06 UCA4815 - Jul 6, 17:10 UTCJul 6, 17:25 UTC15m

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 N21129 page for operator, model, and routing details .

Mode-S A1BFF9 frequently asked

What is Mode-S code A1BFF9?
A1BFF9 is an ICAO 24-bit transponder address. Allocated to United States. Assigned to N21129.
Where is Mode-S A1BFF9 registered?
Mode-S code A1BFF9 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 A1BFF9 broadcasting right now?
No active broadcast right now. Last signal was 12h ago.
Hex, octal, and decimal Mode-S codes: what's the difference?
The same 24-bit identifier expressed in different bases: hex A1BFF9, octal 50337771, decimal 10,600,441.
What flights does A1BFF9 operate?
Mode-S A1BFF9 has broadcast 20 distinct callsigns, including UCA4917, UCA4996, UCA4911, UCA4830, UCA4340.