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 Jul 26, 21:05 UTC
Flights observed
628
Distinct callsigns
20
Country
US
Last broadcast
Jul 26, 21:05 UTC

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 - 9 2026-07-16
UCA4297 CommutAir 8 2026-07-26
UCA4241 CommutAir 8 2026-07-24
UCA4235 CommutAir 8 2026-07-25
UCA4226 CommutAir 8 2026-07-26
UCA4368 CommutAir 7 2026-07-23
UCA4229 CommutAir 7 2026-07-19
UCA4996 - 6 2026-07-12
UCA4963 - 6 2026-07-19
UCA4911 - 6 2026-07-12
UCA4830 - 6 2026-07-11
UCA4824 CommutAir 6 2026-07-24
UCA4340 CommutAir 6 2026-05-29
UCA4977 - 5 2026-06-28
UCA4938 - 5 2026-07-04
UCA4919 CommutAir 5 2026-05-11
UCA4869 CommutAir 5 2026-07-26
UCA4853 - 5 2026-06-29
UCA4812 - 5 2026-07-03
UCA4335 - 5 2026-07-18

Recent flights last 50

DateFlightRouteTakeoffLandingDuration
2026-07-26 UCA4869 IAD → BTV Jul 26, 19:50 UTCJul 26, 21:05 UTC1h 15m
2026-07-26 UCA4338 IAD → CMH Jul 26, 16:50 UTCJul 26, 18:15 UTC1h 25m
2026-07-26 UCA4297 IAD → PVD Jul 26, 14:50 UTCJul 26, 16:00 UTC1h 10m
2026-07-26 UCA4226 LRD → IAH Jul 26, 12:35 UTCJul 26, 13:35 UTC1h 0m
2026-07-26 UCA4226 LRD → IAH Jul 26, 12:43 UTCJul 26, 13:38 UTC55m
2026-07-26 UCA4285 IAH → MFE Jul 26, 00:15 UTCJul 26, 01:10 UTC55m
2026-07-26 UCA4285 IAH → MFE Jul 26, 00:28 UTCJul 26, 01:13 UTC45m
2026-07-25 UCA4365 IAD → BDL Jul 25, 21:55 UTCJul 25, 22:50 UTC55m
2026-07-25 UCA4365 IAD → BDL Jul 25, 22:03 UTCJul 25, 22:42 UTC39m
2026-07-25 UCA4929 LBB → IAH Jul 25, 19:45 UTCJul 25, 20:30 UTC45m
2026-07-25 UCA4338 IAD → CMH Jul 25, 16:55 UTCJul 25, 18:10 UTC1h 15m
2026-07-25 UCA4338 IAD → CMH Jul 25, 17:00 UTCJul 25, 18:10 UTC1h 10m
2026-07-25 UCA4297 IAD → PVD Jul 25, 14:55 UTCJul 25, 16:05 UTC1h 10m
2026-07-25 UCA4299 HSV → IAH Jul 25, 11:55 UTCJul 25, 13:15 UTC1h 20m
2026-07-25 UCA4901 IAH → LBB Jul 25, 02:40 UTCJul 25, 04:10 UTC1h 30m
2026-07-25 UCA4235 ALB → IAD Jul 25, 00:45 UTCJul 25, 01:40 UTC55m
2026-07-25 UCA4235 ALB → IAD Jul 25, 00:45 UTCJul 25, 01:40 UTC55m
2026-07-24 UCA4926 IAD → ALB Jul 24, 23:00 UTCJul 24, 23:55 UTC55m
2026-07-24 UCA4824 IAD → HSV Jul 24, 19:50 UTCJul 24, 20:45 UTC55m
2026-07-24 UCA4241 BTV → IAD Jul 24, 17:05 UTCJul 24, 18:15 UTC1h 10m
2026-07-24 UCA4281 IAD → BTV Jul 24, 14:50 UTCJul 24, 15:05 UTC15m
2026-07-24 UCA4333 IAD → BDL Jul 24, 13:25 UTCJul 24, 13:40 UTC15m
2026-07-24 UCA4861 IAH → LIT Jul 24, 00:00 UTCJul 24, 00:55 UTC55m
2026-07-23 UCA4871 IAD → ROC Jul 23, 22:05 UTCJul 23, 22:55 UTC50m
2026-07-23 UCA4268 MDT → IAD Jul 23, 19:05 UTCJul 23, 19:40 UTC35m
2026-07-23 UCA4372 IAD → MDT Jul 23, 17:20 UTCJul 23, 17:45 UTC25m
2026-07-23 UCA4332 ROA → IAD Jul 23, 14:50 UTCJul 23, 15:35 UTC45m
2026-07-23 UCA4368 IAD → ROA Jul 23, 12:50 UTCJul 23, 13:35 UTC45m
2026-07-23 UCA4368 IAD → ROA Jul 23, 12:51 UTCJul 23, 13:26 UTC35m
2026-07-23 UCA4251 IAD → BUF Jul 23, 10:20 UTCJul 23, 11:05 UTC45m
2026-07-23 UCA4849 OKC → IAH Jul 23, 02:40 UTCJul 23, 03:30 UTC50m
2026-07-23 UCA4238 IAD → BTV Jul 23, 00:15 UTCJul 23, 01:40 UTC1h 25m
2026-07-22 UCA4302 DEN → XNA Jul 22, 22:05 UTCJul 22, 23:10 UTC1h 5m
2026-07-22 UCA4268 - Jul 22, 19:15 UTCJul 22, 19:45 UTC30m
2026-07-22 UCA4372 IAD → MDT Jul 22, 16:55 UTCJul 22, 17:20 UTC25m
2026-07-22 UCA4372 IAD → MDT Jul 22, 17:05 UTCJul 22, 17:20 UTC15m
2026-07-22 UCA4332 ROA → IAD Jul 22, 14:50 UTCJul 22, 15:30 UTC40m
2026-07-22 UCA4368 IAD → ROA Jul 22, 13:10 UTCJul 22, 13:45 UTC35m
2026-07-22 UCA4368 IAD → ROA Jul 22, 12:51 UTCJul 22, 13:43 UTC52m
2026-07-21 UCA4360 IAD → SYR Jul 21, 17:05 UTCJul 21, 18:00 UTC55m
2026-07-21 UCA4360 IAD → SYR Jul 21, 17:05 UTCJul 21, 17:53 UTC48m
2026-07-21 UCA4240 HSV → IAD Jul 21, 13:25 UTCJul 21, 14:55 UTC1h 30m
2026-07-21 UCA4901 - Jul 21, 02:45 UTCJul 21, 04:10 UTC1h 25m
2026-07-20 UCA4235 ALB → IAD Jul 20, 23:55 UTCJul 21, 00:55 UTC1h 0m
2026-07-20 UCA4317 - Jul 20, 17:00 UTCJul 20, 17:55 UTC55m
2026-07-20 UCA4857 - Jul 20, 13:45 UTCJul 20, 14:55 UTC1h 10m
2026-07-20 UCA4270 MFE → IAH Jul 20, 03:35 UTCJul 20, 04:45 UTC1h 10m
2026-07-19 UCA4313 PWM → IAD Jul 19, 23:50 UTCJul 20, 00:45 UTC55m
2026-07-19 UCA4963 - Jul 19, 21:50 UTCJul 19, 22:45 UTC55m
2026-07-19 UCA4963 IAD → GSP Jul 19, 21:43 UTCJul 19, 22:50 UTC1h 7m

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 Jul 26, 21:05 UTC.
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, UCA4297, UCA4241, UCA4235, UCA4226.