Apparatus

Try JFK, AAL1290, BAW, or N225AN.

sensors Mode-S transponder

A4491A

ICAO 24-bit transponder address · allocated to United States

Currently assigned to N37525 · BOEING 737 MAX 9 · operated by WILMINGTON TRUST CO TRUSTEE

Hex
A4491A
Octal
51044432
Decimal
10,766,618
Country
US
Tail
N37525
Type
B39M
Broadcasting now · callsign UAL2254 · 37,000 ft
Flights observed
411
Distinct callsigns
20
Country
US
Last broadcast
17m ago

Current position

A4491A is currently broadcasting. Map zoomed to live position.

Country allocation

The ICAO 24-bit address A4491A 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
UAL1710 - 7 2026-06-25
UAL1644 United Airlines 5 2026-04-24
UAL1039 - 5 2026-06-17
UAL701 United Airlines 4 2026-04-24
UAL665 United Airlines 4 2026-06-10
UAL535 - 4 2026-07-04
UAL1808 United Airlines 4 2026-05-01
UAL1783 - 4 2026-06-22
UAL8260 - 3 2026-06-12
UAL639 - 3 2026-06-22
UAL571 United Airlines 3 2026-04-17
UAL2428 - 3 2026-06-25
UAL2380 - 3 2026-07-05
UAL2182 United Airlines 3 2026-06-13
UAL215 United Airlines 3 2026-07-04
UAL2024 United Airlines 3 2026-05-06
UAL1987 United Airlines 3 2026-04-15
UAL1947 United Airlines 3 2026-06-12
UAL1813 - 3 2026-07-01
UAL1811 - 3 2026-06-29

Recent flights last 50

DateFlightRouteTakeoffLandingDuration
2026-07-14 UAL2254 - Jul 14, 00:20 UTCJul 14, 02:30 UTC2h 10m
2026-07-13 UAL2338 - Jul 13, 20:30 UTCJul 13, 22:15 UTC1h 45m
2026-07-13 UAL2338 MSN → DEN Jul 13, 20:27 UTCJul 13, 22:10 UTC1h 43m
2026-07-13 UAL2368 - Jul 13, 17:10 UTCJul 13, 19:00 UTC1h 50m
2026-07-13 UAL595 AUS → DEN Jul 13, 13:43 UTCJul 13, 15:22 UTC1h 39m
2026-07-13 UAL595 AUS → DEN Jul 13, 13:40 UTCJul 13, 15:25 UTC1h 45m
2026-07-13 UAL1943 DEN → AUS Jul 13, 02:55 UTCJul 13, 04:35 UTC1h 40m
2026-07-12 UAL1136 CUN → DEN Jul 12, 21:05 UTCJul 13, 00:45 UTC3h 40m
2026-07-12 UAL1167 - Jul 12, 17:40 UTCJul 12, 18:10 UTC30m
2026-07-12 UAL1167 IAH → CUN Jul 12, 17:50 UTCJul 12, 19:25 UTC1h 35m
2026-07-12 UAL2168 - Jul 12, 12:20 UTCJul 12, 15:55 UTC3h 35m
2026-07-11 UAL1212 - Jul 11, 15:55 UTCJul 11, 23:35 UTC7h 40m
2026-07-11 UAL1724 KOA → SFO Jul 11, 13:05 UTCJul 11, 13:40 UTC35m
2026-07-11 UAL1724 KOA → SFO Jul 11, 08:55 UTCJul 11, 09:05 UTC10m
2026-07-11 UAL1723 - Jul 11, 05:05 UTCJul 11, 05:20 UTC15m
2026-07-11 UAL1723 - Jul 11, 00:30 UTCJul 11, 01:00 UTC30m
2026-07-10 UAL1074 BOS → SFO Jul 10, 16:20 UTCJul 10, 22:15 UTC5h 55m
2026-07-10 UAL641 IAD → BOS Jul 10, 13:05 UTCJul 10, 14:10 UTC1h 5m
2026-07-10 UAL8223 SFO → IAD Jul 10, 00:24 UTCJul 10, 04:55 UTC4h 31m
2026-07-10 UAL8223 SFO → IAD Jul 10, 00:25 UTCJul 10, 05:00 UTC4h 35m
2026-07-09 UAL1434 IAD → SFO Jul 9, 17:35 UTCJul 9, 22:55 UTC5h 20m
2026-07-09 UAL1709 - Jul 9, 13:45 UTCJul 9, 15:05 UTC1h 20m
2026-07-09 UAL1815 SFO → BNA Jul 9, 07:25 UTCJul 9, 11:15 UTC3h 50m
2026-07-09 UAL1815 SFO → BNA Jul 9, 07:22 UTCJul 9, 11:16 UTC3h 54m
2026-07-08 UAL2400 - Jul 8, 22:45 UTCJul 9, 04:35 UTC5h 50m
2026-07-08 UAL2647 DCA → IAH Jul 8, 15:50 UTCJul 8, 21:10 UTC5h 20m
2026-07-07 UAL1931 SJD → SFO Jul 7, 20:19 UTCJul 7, 22:55 UTC2h 36m
2026-07-07 UAL1931 - Jul 7, 16:10 UTCJul 7, 22:55 UTC6h 45m
2026-07-07 UAL1685 - Jul 7, 13:15 UTCJul 7, 13:50 UTC35m
2026-07-07 UAL1684 SFO → LIH Jul 7, 01:56 UTCJul 7, 06:24 UTC4h 28m
2026-07-07 UAL1684 - Jul 7, 01:35 UTCJul 7, 02:00 UTC25m
2026-07-06 UAL487 - Jul 6, 10:40 UTCJul 6, 14:20 UTC3h 40m
2026-07-05 UAL2305 - Jul 5, 23:55 UTCJul 6, 03:15 UTC3h 20m
2026-07-05 UAL650 - Jul 5, 17:10 UTCJul 5, 21:45 UTC4h 35m
2026-07-05 UAL2380 - Jul 5, 04:40 UTCJul 5, 04:55 UTC15m
2026-07-05 UAL2380 SFO → HNL Jul 5, 00:11 UTCJul 5, 04:51 UTC4h 40m
2026-07-04 UAL2380 - Jul 4, 23:55 UTCJul 5, 00:25 UTC30m
2026-07-04 UAL2756 - Jul 4, 18:05 UTCJul 4, 21:40 UTC3h 35m
2026-07-04 UAL535 - Jul 4, 14:20 UTCJul 4, 16:25 UTC2h 5m
2026-07-04 UAL535 ORD → IAH Jul 4, 14:21 UTCJul 4, 16:25 UTC2h 4m
2026-07-04 UAL215 IAD → SFO Jul 4, 10:25 UTCJul 4, 12:30 UTC2h 5m
2026-07-04 UAL215 IAD → SFO Jul 4, 10:28 UTCJul 4, 12:07 UTC1h 39m
2026-07-04 UAL636J ORD → BTV Jul 4, 00:40 UTCJul 4, 02:20 UTC1h 40m
2026-07-03 UAL1475 - Jul 3, 20:35 UTCJul 3, 22:50 UTC2h 15m
2026-07-03 UAL1606 ORD → BOS Jul 3, 16:01 UTCJul 3, 17:48 UTC1h 47m
2026-07-03 UAL1606 ORD → BOS Jul 3, 15:55 UTCJul 3, 17:45 UTC1h 50m
2026-07-03 UAL1554 SJC → DEN Jul 3, 11:05 UTCJul 3, 13:35 UTC2h 30m
2026-07-03 UAL1554 SJC → DEN Jul 3, 11:12 UTCJul 3, 13:20 UTC2h 8m
2026-07-02 UAL2618 - Jul 2, 22:00 UTCJul 3, 00:30 UTC2h 30m
2026-07-02 UAL1983 - Jul 2, 17:00 UTCJul 2, 19:45 UTC2h 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 N37525 page for operator, model, and routing details .

Mode-S A4491A frequently asked

What is Mode-S code A4491A?
A4491A is an ICAO 24-bit transponder address. Allocated to United States. Assigned to N37525.
Where is Mode-S A4491A registered?
Mode-S code A4491A 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 A4491A broadcasting right now?
Yes. Mode-S A4491A is currently airborne.
Hex, octal, and decimal Mode-S codes: what's the difference?
The same 24-bit identifier expressed in different bases: hex A4491A, octal 51044432, decimal 10,766,618.
What flights does A4491A operate?
Mode-S A4491A has broadcast 20 distinct callsigns, including UAL1710, UAL1644, UAL1039, UAL701, UAL665.