A decoder built from real radio
Instead of relying on one rigid DSP path, ACARSd used multiple decoder passes, empirical code tables, CRC validation and adaptive table ordering to extract messages from imperfect analog audio.
Digital aviation archaeology • 2003—2026
ACARSdDECODER • SERVER • NETWORK
Before crowd-sourced aircraft tracking became mainstream, ACARSd connected distributed radio receivers over the Internet, shared live ACARS traffic, enriched it with databases and let remote clients watch aircraft activity from stations around the world.
75 km
LIVE 1090 MHz • 75 KM …
MUSEUM RECOVERY • 2026
What happened after I simply walked away?
The aviation project ended, but the pattern did not. KjM is still a programmer at INLINE, with Dr. Armin Zundel still both boss and close friend. Plumeria became a specialist business — and eventually a nearly 300-page book — while years of travelling to Bali grew into another business around Balinese products.
The new epilogue also looks back at the people from the ACARSd years: some friendships never broke, some contacts became quieter, and rebuilding the museum has unexpectedly brought many of them close again.
Now online • historical database
Search the recovered ACARS archive.
The restored database can now be searched directly by aircraft registration, flight number, six-character ICAO24 address and date range. Aircraft details are enriched from the recovered reference database while the original historical message records remain untouched.
Recovered reference data • 2008 snapshot
Have an old Mode-S hex code?
The museum now includes a dedicated ICAO24 Aircraft Lookup. Enter a six-character Mode-S hexadecimal address and resolve it against the recovered historical aircraft database — including registrations, types, construction numbers and operator data that may no longer appear in current fleet lists.
Example from the recovered archive
47161A → HA-LOA
One of the rediscovered mappings links the Mode-S address 47161A to Malév Boeing 737 HA-LOA. The associated aircraft record identifies a Boeing 737-7Q8, construction number 28254.
The signature everyone knew
*<SYN><SYN><SOH> ACARS BEGINS HERE
For anyone who spent nights watching ACARS traffic scroll across a terminal, this sequence was instantly familiar: a leading *, two SYN characters and SOH — Start of Header. Before registrations, flight numbers and message text appeared, this was the little signature that said a real ACARS frame was beginning.
A small museum for an early networked flight-data system.
This site preserves the history and engineering of ACARSd. Most of it is reconstructed from original source code, CVS/RCS history, website archives and contemporary project notes. Since 30 August 2026, one small local receiver has also been allowed back into the museum.
Receivers became Internet servers
A station could decode locally and serve live traffic to remote clients. Public server lists, web access and central reporting turned isolated scanners into a distributed community network.
From messages to flight context
Aircraft, airline, routing, position, fleet and image data were combined with decoded traffic. Later work also bridged into Mode-S/SBS data through the HomeRadar libraries.
The original ambition
“A Linux decoder, with aircraft pictures, a server for other users and a searchable database.”
That goal was written down while the actual decoder still did not work. It is why ACARSd was never merely a sound-card utility: the network and database were part of the idea from the beginning.
The first successful live decode was HA-LOC, a new Malév Boeing 737 on its delivery flight.
Read the reconstructed story →
Networked aviation data
The architecture came years before today’s familiar crowd-sourced flight maps.
ACARS is not ADS-B and ACARSd was not a continuous radar in the modern sense. But the core Internet model was strikingly familiar: many geographically separated receivers, shared live data, remote clients, discovery of public stations and a central historical data service.
TCP/2202PUBLIC SERVERSCLIENTNGWEB SERVERPUBLIC DB
30 August 2026 • receiving again
What does KjM see today?
An old RTL-SDR stick, a Raspberry Pi 5 and readsb have turned one corner of the museum back into an actual receiving station. The new page contains only aircraft heard by the local antenna in Balatonszárszó — no external tracking network.
Search today's local receiver data → Open the full live radar →
A very small live epilogue
The archive listens.
Every fifteen minutes the station contributes its latest locally received aircraft snapshots to the restored ACARSd database.
V22.3 • 2026 recovery completed
72,788,180 ACARS records came back from a broken server.
A failing ext3 server still contained 1,729,775 binary client uploads that had never reached the later database-processing stage. In 2026 the files were rescued in blocks, decoded from the original ACARSd collection structure and checked individually.
1,723,977 uploads decoded successfully — 99.6648% — producing 72,788,180 recovered ACARS records. The WORLD ACARS Report import is now complete as well. A verified database count on 30 August 2026 returned 114,328,158 searchable message rows. The public museum search is online, and the restored local receiver is adding new 2026 observations again.
1.65: 292,417 uploads1.66: 1,431,560 uploads5,798 decode errors
Unexpected epilogue
ACARSd was still sending data in 2026.
After the old server was temporarily reachable again, an ACARSd 1.70RC3 installation uploaded a real collection on 26 August 2026. Other surviving 1.65Win clients also began asking the original lookup endpoints for aircraft and flight information.
V19 • recovered documentation
The software came with a manual — and the later library came with sixteen examples.
A recovered 23-page ACARSd manual documents the early decoder/server in remarkable detail. The later libhomeradar archive goes one step further: sixteen C examples show other developers how to connect receivers, handle events, enrich contacts, filter aircraft, calculate distance and feed network services.
The V19 exhibit also adds nine ACARSd screenshots from 2 March 2006, including the GUI, Linux console, statistics and the hidden games.
2010 • ATLAS for FlightGlobal
The ACARSd idea evolved into a browser-based global flight map.
Recovered CVS sources identify the 2010 commercial project as ATLAS for FlightGlobal. Built in Adobe Flex/Flash on Google Maps, it consumed community SBS/Mode-S feeds and already rendered aircraft by type and airline colours.
Its icon system contained distinct silhouettes for the Boeing 747, Airbus A380, A340, MD-11, 767, A320/737 family, regional aircraft and later the 757, 787 and A350. Body, wings, tail and engines could be coloured separately for an airline.
When hobby data became evidence
A Dutch meeting turned scraped flight translations into a two-way data exchange.
EUclaim supplied ACARSd with flight-number translation data; in return it received the live ACARS stream. A public court record later documents an EUclaim case against Martinair over flight MP815 to Canada, delayed by more than 24 hours — a remarkable match to a case remembered from the ACARSd years.
A 2010 European Commission study independently records that EUclaim used ADS-B/ACARS transmissions among its evidence sources.
Community archive
Were you part of ACARSd?
Former users, server operators, testers and contributors are invited to add their memories to the museum.
2003 • already beyond the decoder
A browser live client, a developer API and third-party software.
The restored archive revealed a forgotten early experiment: ACARS LIVE, a browser-based live client from 2003 that pulled ACARS traffic through a small proxy daemon and even fetched aircraft images from FYSB. In September 2003 a formal developer API already exposed structured network operations, and the independent Java client JACARS later connected to the same network.
*<SYN><SYN><SOH>
↓
ACARSd
↓
TCP network / API
↙ ↓ ↘
Tcl/Tk Browser Java
Client ACARS LIVE JACARS
↓
FYSB imagesRecovered in V13
From one decoder to a reusable aircraft-data platform.
Newly recovered CVS trees show the later evolution with unusual clarity: libacarsd2 turned ACARSd technology into a reusable library; mACARS became a small Windows front-end; winsend2 merged ACARS, SBS-1 and RadarBox data; and FlightShare2 distilled that large toolkit into the deliberately simple feeder FlightGlobal wanted for ATLAS.
ACARSd→libacarsd2→mACARS / winsend2→ATLAS→FlightShare2
Messages, not radar
What could you actually see on ACARS?
Positions were only one small part of the system. The recovered archive contains oceanic clearances, routes, engine and performance data, maintenance faults, diversions, dispatch traffic and medical requests — as well as proprietary payloads that remained unreadable even after the ACARS frame was correctly decoded.
SOFTWARE ARCHIVE
The original downloads are back.
Historical ACARSd releases, Windows builds, ClientNG, ACARSdClient, libraries and support files are available again under the original /download/ path.
Source archaeology, not mythology.
Claims on this site are deliberately separated into contemporary documentation, facts visible in the source/CVS history, and memories supplied by the original author decades later. Where a date or technical detail is uncertain, it is marked as such.
December 2004 story
The original project story documents the accidental ANAD report, the scanner odyssey, the first decoder, the ANAD comparison, CRC support and the Windows port.
libacarsd + libacarsd2
RCS/CVS files preserve the actual multi-pass decoder, code tables, CRC routines, FFT experiments and revision history after the decoder was separated into a library.
acarsd.org
Original server pages, API documentation, release notes, public database tools and historical web content reveal how broad the project had become.
Stories from the data
AF447, Germanwings 9525 — and the unexpected value of an archive.
Years after ACARSd began as a hobby decoder, its historical records and flight data were sometimes consulted in the aftermath of major aviation events. These recollections are preserved with a strict distinction between memory and independently established facts.