Apparatus

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sensors Mode-S transponder

8991A4

ICAO 24-bit transponder address · allocated to Taiwan

Currently assigned to B-18725 · BOEING 747-400

Hex
8991A4
Octal
42310644
Decimal
9,015,716
Country
TW
Tail
B-18725
Type
B744
No current signal · last broadcast Jul 26, 23:00 UTC
Flights observed
280
Distinct callsigns
20
Country
TW
Last broadcast
Jul 26, 23:00 UTC

Last known position

Most recent position reported by Mode-S 8991A4.

Country allocation

The ICAO 24-bit address 8991A4 falls within the block assigned to Taiwan (TW) by ICAO Annex 10, Volume III. Every aircraft registered in Taiwan 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
CAL5267 - 18 2026-07-20
CAL5265 China Airlines 18 2026-07-25
CAL5266 China Airlines 17 2026-07-24
CAL6865 China Airlines 10 2026-07-18
CAL5268 China Airlines 10 2026-07-19
CAL5240 China Airlines 10 2026-07-26
CAL5239 China Airlines 9 2026-07-26
CAL6888 China Airlines 8 2026-07-23
CAL5233 - 8 2026-06-16
CAL6887 China Airlines 7 2026-07-23
CAL5927 - 7 2026-07-02
CAL5226 China Airlines 7 2026-04-16
CAL5225 China Airlines 7 2026-04-17
CAL6866 China Airlines 6 2026-07-18
CAL5928 - 6 2026-07-02
CAL5898 - 6 2026-07-22
CAL5884 - 6 2026-07-08
CAL5878 China Airlines 6 2026-07-21
CAL5234 - 6 2026-06-15
CAL6881 - 5 2026-07-07

Recent flights last 50

DateFlightRouteTakeoffLandingDuration
2026-07-26 CAL5239 ORD → ANC Jul 26, 18:00 UTCJul 26, 23:00 UTC5h 0m
2026-07-26 CAL5240 TPE → ANC Jul 26, 08:55 UTCJul 26, 14:15 UTC5h 20m
2026-07-25 CAL5240 TPE → ANC Jul 25, 23:45 UTCJul 26, 07:35 UTC7h 51m
2026-07-25 CAL5240 TPE → ANC Jul 25, 23:00 UTCJul 25, 23:15 UTC15m
2026-07-25 CAL5265 SFO → ANC Jul 25, 14:20 UTCJul 25, 14:50 UTC30m
2026-07-25 CAL5265 SFO → ANC Jul 25, 05:35 UTCJul 25, 13:20 UTC7h 45m
2026-07-24 CAL5265 SFO → ANC Jul 24, 21:00 UTCJul 25, 03:05 UTC6h 5m
2026-07-24 CAL5266 ANC → DFW Jul 24, 12:30 UTCJul 24, 17:55 UTC5h 25m
2026-07-24 CAL5266 ANC → DFW Jul 24, 02:50 UTCJul 24, 11:00 UTC8h 10m
2026-07-23 CAL6888 TPE → TPE Jul 23, 21:15 UTCJul 23, 22:30 UTC1h 15m
2026-07-23 CAL6888 TPE → TPE Jul 23, 20:25 UTCJul 23, 20:35 UTC10m
2026-07-23 CAL6887 TPE → HAN Jul 23, 17:35 UTCJul 23, 17:45 UTC10m
2026-07-23 CAL6887 TPE → HAN Jul 23, 15:30 UTCJul 23, 16:40 UTC1h 10m
2026-07-23 CAL5705 - Jul 23, 11:25 UTCJul 23, 11:45 UTC20m
2026-07-23 CAL5705 - Jul 23, 09:00 UTCJul 23, 10:10 UTC1h 10m
2026-07-23 CAL5706 TPE → NRT Jul 23, 03:40 UTCJul 23, 06:40 UTC3h 0m
2026-07-22 CAL5898 - Jul 22, 23:40 UTCJul 23, 00:05 UTC25m
2026-07-22 CAL5897 TPE → PVG Jul 22, 15:50 UTCJul 22, 16:30 UTC40m
2026-07-21 CAL5878 SIN → SGN Jul 21, 05:30 UTCJul 21, 12:45 UTC7h 15m
2026-07-21 CAL5877 TPE → SIN Jul 21, 02:55 UTCJul 21, 03:15 UTC20m
2026-07-20 CAL5877 TPE → SIN Jul 20, 23:30 UTCJul 21, 00:25 UTC54m
2026-07-20 CAL5267 DFW → ANC Jul 20, 19:00 UTCJul 20, 19:20 UTC20m
2026-07-20 CAL5267 DFW → ANC Jul 20, 10:20 UTCJul 20, 18:00 UTC7h 40m
2026-07-20 CAL5267 DFW → ANC Jul 20, 01:10 UTCJul 20, 07:15 UTC6h 5m
2026-07-19 CAL5268 ANC → DFW Jul 19, 15:35 UTCJul 19, 21:20 UTC5h 45m
2026-07-19 CAL5268 ANC → DFW Jul 19, 05:20 UTCJul 19, 13:50 UTC8h 30m
2026-07-18 CAL5896 CAN → TPE Jul 18, 22:15 UTCJul 18, 23:55 UTC1h 40m
2026-07-18 CAL5895 - Jul 18, 18:05 UTCJul 18, 19:10 UTC1h 5m
2026-07-18 CAL6866 SIN → PEN Jul 18, 14:40 UTCJul 18, 15:50 UTC1h 10m
2026-07-18 CAL6866 SIN → PEN Jul 18, 11:40 UTCJul 18, 11:50 UTC10m
2026-07-18 CAL6865 SIN → PEN Jul 18, 08:05 UTCJul 18, 09:05 UTC1h 0m
2026-07-18 CAL6865 SIN → PEN Jul 18, 01:39 UTCJul 18, 05:20 UTC3h 41m
2026-07-17 CAL6872 - Jul 17, 07:14 UTCJul 17, 08:35 UTC1h 20m
2026-07-16 CAL6871 TPE → SIN Jul 16, 21:25 UTCJul 17, 01:09 UTC3h 45m
2026-07-16 CAL6888 - Jul 16, 16:44 UTCJul 16, 18:05 UTC1h 20m
2026-07-16 CAL6888 - Jul 16, 15:49 UTCJul 16, 16:00 UTC10m
2026-07-16 CAL6887 - Jul 16, 11:05 UTCJul 16, 12:05 UTC1h 0m
2026-07-16 CAL6884 - Jul 16, 06:40 UTCJul 16, 07:50 UTC1h 10m
2026-07-16 CAL6884 - Jul 16, 04:30 UTCJul 16, 04:40 UTC10m
2026-07-16 CAL6884 - Jul 16, 00:05 UTCJul 16, 02:05 UTC2h 0m
2026-07-15 CAL6883 - Jul 15, 18:05 UTCJul 15, 21:45 UTC3h 40m
2026-07-15 CAL6844 HKG → TPE Jul 15, 12:55 UTCJul 15, 14:25 UTC1h 30m
2026-07-15 CAL6843 TPE → HKG Jul 15, 08:00 UTCJul 15, 09:40 UTC1h 40m
2026-07-14 CAL5997 - Jul 14, 20:40 UTCJul 15, 05:05 UTC8h 24m
2026-07-14 CAL5586 - Jul 14, 16:35 UTCJul 14, 17:50 UTC1h 15m
2026-07-14 CAL5586 - Jul 14, 13:35 UTCJul 14, 13:45 UTC10m
2026-07-14 CAL5871 - Jul 14, 09:55 UTCJul 14, 10:15 UTC20m
2026-07-14 CAL5871 - Jul 14, 06:25 UTCJul 14, 07:25 UTC1h 0m
2026-07-13 CAL5239 ANC → TPE Jul 13, 17:05 UTCJul 14, 02:10 UTC9h 5m
2026-07-13 CAL5239 ORD → ANC Jul 13, 09:45 UTCJul 13, 15:25 UTC5h 40m

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 B-18725 page for operator, model, and routing details .

Mode-S 8991A4 frequently asked

What is Mode-S code 8991A4?
8991A4 is an ICAO 24-bit transponder address. Allocated to Taiwan. Assigned to B-18725.
Where is Mode-S 8991A4 registered?
Mode-S code 8991A4 is allocated to Taiwan (TW). All aircraft registered there receive a Mode-S address from a fixed block defined by ICAO Annex 10.
Is 8991A4 broadcasting right now?
No active broadcast right now. Last signal was Jul 26, 23:00 UTC.
Hex, octal, and decimal Mode-S codes: what's the difference?
The same 24-bit identifier expressed in different bases: hex 8991A4, octal 42310644, decimal 9,015,716.
What flights does 8991A4 operate?
Mode-S 8991A4 has broadcast 20 distinct callsigns, including CAL5267, CAL5265, CAL5266, CAL6865, CAL5268.