Apparatus

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sensors Mode-S transponder

4D21BD

ICAO 24-bit transponder address · allocated to Malta

Currently assigned to 9H-OJO

Hex
4D21BD
Octal
23220675
Decimal
5,054,909
Country
MT
Tail
9H-OJO
Type
GLEX
No current signal · last broadcast 2d ago
Flights observed
6
Distinct callsigns
2
Country
MT
Last broadcast
2d ago

Last known position

Most recent position reported by Mode-S 4D21BD.

Country allocation

The ICAO 24-bit address 4D21BD falls within the block assigned to Malta (MT) by ICAO Annex 10, Volume III. Every aircraft registered in Malta 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 2 distinct

Callsign Airline Flights Last seen
9HIOO - 5 2026-05-18
RYR2EE Ryanair 1 2026-05-11

Recent flights last 6

DateFlightRouteTakeoffLandingDuration
2026-05-18 9HIOO OBF → NUE May 18, 13:35 UTCMay 18, 14:00 UTC25m
2026-05-18 9HIOO NUE → OBF May 18, 11:45 UTCMay 18, 12:15 UTC30m
2026-05-11 RYR2EE BCN → MAN May 11, 13:50 UTCMay 11, 14:00 UTC10m
2026-05-07 9HIOO - May 7, 13:45 UTCMay 7, 14:10 UTC25m
2026-05-07 9HIOO NUE → OBF May 7, 12:20 UTCMay 7, 12:45 UTC25m
2026-05-06 9HIOO NUE → NUE May 6, 16:15 UTCMay 6, 17:30 UTC1h 15m

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 9H-OJO page for operator, model, and routing details .

Mode-S 4D21BD frequently asked

What is Mode-S code 4D21BD?
4D21BD is an ICAO 24-bit transponder address. Allocated to Malta. Assigned to 9H-OJO.
Where is Mode-S 4D21BD registered?
Mode-S code 4D21BD is allocated to Malta (MT). All aircraft registered there receive a Mode-S address from a fixed block defined by ICAO Annex 10.
Is 4D21BD broadcasting right now?
No active broadcast right now. Last signal was 2d ago.
Hex, octal, and decimal Mode-S codes: what's the difference?
The same 24-bit identifier expressed in different bases: hex 4D21BD, octal 23220675, decimal 5,054,909.
What flights does 4D21BD operate?
Mode-S 4D21BD has broadcast 2 distinct callsigns, including 9HIOO, RYR2EE.