Apparatus

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sensors Mode-S transponder

A3F621

ICAO 24-bit transponder address · allocated to United States

Currently assigned to N35407 · BOEING 737-900 · operated by UNITED AIRLINES INC

Hex
A3F621
Octal
50773041
Decimal
10,745,377
Country
US
Tail
N35407
Type
B739
No current signal · last broadcast Jul 26, 22:15 UTC
Flights observed
467
Distinct callsigns
20
Country
US
Last broadcast
Jul 26, 22:15 UTC

Last known position

Most recent position reported by Mode-S A3F621.

Country allocation

The ICAO 24-bit address A3F621 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
UAL2406 United Airlines 15 2026-07-18
UAL1936 United Airlines 13 2026-07-26
UAL1563 United Airlines 11 2026-07-26
UAL575 United Airlines 10 2026-07-22
UAL315 United Airlines 10 2026-07-26
UAL2662 - 10 2026-07-09
UAL2124 United Airlines 10 2026-07-21
UAL1895 United Airlines 10 2026-05-20
UAL496 - 9 2026-07-11
UAL2253 United Airlines 9 2026-07-22
UAL1950 United Airlines 9 2026-07-25
UAL1927 United Airlines 9 2026-07-25
UAL740 United Airlines 8 2026-07-25
UAL2310 - 8 2026-07-18
UAL1609 United Airlines 8 2026-07-22
UAL1388 - 8 2026-07-22
UAL1345 United Airlines 8 2026-07-24
UAL678 United Airlines 7 2026-07-25
UAL491 United Airlines 7 2026-07-24
UAL2105 - 7 2026-07-24

Recent flights last 50

DateFlightRouteTakeoffLandingDuration
2026-07-26 UAL1444 SFO → IAH Jul 26, 21:25 UTCJul 26, 22:15 UTC50m
2026-07-26 UAL315 FLL → IAD Jul 26, 17:25 UTCJul 26, 19:50 UTC2h 25m
2026-07-26 UAL1936 SAV → EWR Jul 26, 13:05 UTCJul 26, 16:05 UTC3h 0m
2026-07-26 UAL1563 LIH → SFO Jul 26, 02:00 UTCJul 26, 04:40 UTC2h 40m
2026-07-25 UAL1927 ORD → EWR Jul 25, 20:25 UTCJul 26, 00:10 UTC3h 45m
2026-07-25 UAL1927 ORD → EWR Jul 25, 20:12 UTCJul 25, 23:59 UTC3h 47m
2026-07-25 UAL740 SEA → DEN Jul 25, 14:45 UTCJul 25, 18:30 UTC3h 45m
2026-07-25 UAL678 LAS → SFO Jul 25, 12:10 UTCJul 25, 13:05 UTC55m
2026-07-25 UAL678 LAS → SFO Jul 25, 12:12 UTCJul 25, 13:05 UTC53m
2026-07-25 UAL1950 KOA → SFO Jul 25, 01:50 UTCJul 25, 02:35 UTC45m
2026-07-24 UAL1752 EWR → MCO Jul 24, 21:20 UTCJul 24, 23:20 UTC2h 0m
2026-07-24 UAL1752 EWR → MCO Jul 24, 21:25 UTCJul 24, 23:14 UTC1h 49m
2026-07-24 UAL1345 MIA → EWR Jul 24, 17:50 UTCJul 24, 19:50 UTC2h 0m
2026-07-24 UAL2105 - Jul 24, 15:00 UTCJul 24, 15:50 UTC50m
2026-07-24 UAL491 BZN → DEN Jul 24, 12:45 UTCJul 24, 13:35 UTC50m
2026-07-24 UAL2449 SJC → IAH Jul 24, 00:00 UTCJul 24, 02:40 UTC2h 40m
2026-07-23 UAL1971 EWR → SAT Jul 23, 19:35 UTCJul 23, 22:10 UTC2h 35m
2026-07-23 UAL2812 ORD → EWR Jul 23, 15:50 UTCJul 23, 18:00 UTC2h 10m
2026-07-23 UAL2078 - Jul 23, 01:25 UTCJul 23, 03:30 UTC2h 5m
2026-07-22 UAL1609 IAH → SFO Jul 22, 22:50 UTCJul 22, 23:35 UTC45m
2026-07-22 UAL1388 - Jul 22, 20:30 UTCJul 22, 21:10 UTC40m
2026-07-22 UAL2253 RDU → IAD Jul 22, 17:10 UTCJul 22, 18:00 UTC50m
2026-07-22 UAL575 BOS → ORD Jul 22, 15:00 UTCJul 22, 15:50 UTC50m
2026-07-22 UAL678 LAS → SFO Jul 22, 12:20 UTCJul 22, 13:20 UTC1h 0m
2026-07-22 UAL1950 KOA → SFO Jul 22, 04:25 UTCJul 22, 05:10 UTC45m
2026-07-21 UAL1927 ORD → EWR Jul 21, 20:15 UTCJul 21, 23:55 UTC3h 40m
2026-07-21 UAL740 SEA → DEN Jul 21, 14:45 UTCJul 21, 18:20 UTC3h 35m
2026-07-21 UAL2124 PDX → SFO Jul 21, 12:10 UTCJul 21, 13:00 UTC50m
2026-07-21 UAL8101 - Jul 21, 01:45 UTCJul 21, 02:35 UTC50m
2026-07-20 UAL1609 IAH → SFO Jul 20, 22:50 UTCJul 20, 23:35 UTC45m
2026-07-20 UAL1388 - Jul 20, 20:10 UTCJul 20, 20:55 UTC45m
2026-07-20 UAL2253 RDU → IAD Jul 20, 17:20 UTCJul 20, 18:10 UTC50m
2026-07-20 UAL575 BOS → ORD Jul 20, 15:10 UTCJul 20, 16:00 UTC50m
2026-07-20 UAL678 - Jul 20, 12:20 UTCJul 20, 13:20 UTC1h 0m
2026-07-20 UAL1950 KOA → SFO Jul 20, 02:05 UTCJul 20, 02:50 UTC45m
2026-07-19 UAL1949 ORD → DCA Jul 19, 20:30 UTCJul 19, 23:55 UTC3h 25m
2026-07-19 UAL2773 - Jul 19, 15:25 UTCJul 19, 18:40 UTC3h 15m
2026-07-19 UAL2399 - Jul 19, 11:20 UTCJul 19, 13:05 UTC1h 45m
2026-07-19 UAL2846 ORD → ABQ Jul 19, 02:20 UTCJul 19, 04:00 UTC1h 40m
2026-07-18 UAL2406 LAX → SFO Jul 18, 18:25 UTCJul 18, 20:20 UTC1h 55m
2026-07-18 UAL2310 - Jul 18, 15:00 UTCJul 18, 17:00 UTC2h 0m
2026-07-18 UAL2124 - Jul 18, 12:50 UTCJul 18, 13:35 UTC45m
2026-07-18 UAL1696 - Jul 18, 02:00 UTCJul 18, 02:50 UTC51m
2026-07-17 UAL1609 - Jul 17, 22:55 UTCJul 17, 23:39 UTC45m
2026-07-17 UAL1609 IAH → SFO Jul 17, 22:39 UTCJul 17, 23:32 UTC53m
2026-07-17 UAL1388 - Jul 17, 20:10 UTCJul 17, 21:10 UTC1h 0m
2026-07-17 UAL1388 IAH → DFW Jul 17, 20:13 UTCJul 17, 21:03 UTC50m
2026-07-17 UAL462 - Jul 17, 15:05 UTCJul 17, 18:50 UTC3h 45m
2026-07-17 UAL462 PDX → IAH Jul 17, 14:25 UTCJul 17, 18:47 UTC4h 22m
2026-07-17 UAL1420 - Jul 17, 02:34 UTCJul 17, 06:20 UTC3h 45m

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 N35407 page for operator, model, and routing details .

Mode-S A3F621 frequently asked

What is Mode-S code A3F621?
A3F621 is an ICAO 24-bit transponder address. Allocated to United States. Assigned to N35407.
Where is Mode-S A3F621 registered?
Mode-S code A3F621 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 A3F621 broadcasting right now?
No active broadcast right now. Last signal was Jul 26, 22:15 UTC.
Hex, octal, and decimal Mode-S codes: what's the difference?
The same 24-bit identifier expressed in different bases: hex A3F621, octal 50773041, decimal 10,745,377.
What flights does A3F621 operate?
Mode-S A3F621 has broadcast 20 distinct callsigns, including UAL2406, UAL1936, UAL1563, UAL575, UAL315.