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The Python ADS-B/Mode-S Decoder


PyModeS is a Python library designed to decode Mode-S (including ADS-B) messages. It can be imported to your python project or used as a standalone tool to view and save live traffic data.

This is a project created by Junzi Sun, who works at `TU Delft <>`_, `Aerospace Engineering Faculty <>`_, `CNS/ATM research group <>`_. It is supported by many `contributors <>`_ from different institutions.


pyModeS supports the decoding of following types of messages:

- DF4 / DF20: Altitude code
- DF5 / DF21: Identity code (squawk code)

- DF17 / DF18: Automatic Dependent Surveillance-Broadcast (ADS-B)

- TC=1-4 / BDS 0,8: Aircraft identification and category
- TC=5-8 / BDS 0,6: Surface position
- TC=9-18 / BDS 0,5: Airborne position
- TC=19 / BDS 0,9: Airborne velocity
- TC=28 / BDS 6,1: Airborne status [to be implemented]
- TC=29 / BDS 6,2: Target state and status information [to be implemented]
- TC=31 / BDS 6,5: Aircraft operational status [to be implemented]

- DF20 / DF21: Mode-S Comm-B messages

- BDS 1,0: Data link capability report
- BDS 1,7: Common usage GICB capability report
- BDS 2,0: Aircraft identification
- BDS 3,0: ACAS active resolution advisory
- BDS 4,0: Selected vertical intention
- BDS 4,4: Meteorological routine air report (experimental)
- BDS 4,5: Meteorological hazard report (experimental)
- BDS 5,0: Track and turn report
- BDS 6,0: Heading and speed report

If you find this project useful for your research, please considering cite this tool as::

author={J. {Sun} and H. {V\^u} and J. {Ellerbroek} and J. M. {Hoekstra}},
journal={IEEE Transactions on Intelligent Transportation Systems},
title={pyModeS: Decoding Mode-S Surveillance Data for Open Air Transportation Research},

Check out and contribute to this open-source project at:

Detailed manual on Mode-S decoding is published at:

The API documentation of pyModeS is at:

Basic installation

Installation examples::

# stable version
pip install pyModeS

# conda (compiled) version
conda install -c conda-forge pymodes

# development version
pip install git+

Dependencies ``numpy``, and ``pyzmq`` are installed automatically during previous installations processes.

If you need to connect pyModeS to a RTL-SDR receiver, ``pyrtlsdr`` need to be installed manually::

pip install pyrtlsdr

Advanced installation (using c modules)

If you want to make use of the (faster) c module, install ``pyModeS`` as follows::

# conda (compiled) version
conda install -c conda-forge pymodes

# stable version
pip install pyModeS

# development version
git clone
cd pyModeS
poetry install -E rtlsdr

View live traffic (modeslive)

General usage::

$ modeslive [-h] --source SOURCE [--connect SERVER PORT DATAYPE]
[--latlon LAT LON] [--show-uncertainty] [--dumpto DUMPTO]

-h, --help show this help message and exit
--source SOURCE Choose data source, "rtlsdr" or "net"
Define server, port and data type. Supported data
types are: ['raw', 'beast', 'skysense']
--latlon LAT LON Receiver latitude and longitude, needed for the surface
position, default none
--show-uncertainty Display uncertainty values, default off
--dumpto DUMPTO Folder to dump decoded output, default none

Live with RTL-SDR

If you have an RTL-SDR receiver connected to your computer, you can use the ``rtlsdr`` source switch (require ``pyrtlsdr`` package), with command::

$ modeslive --source rtlsdr

Live with network data

If you want to connect to a TCP server that broadcast raw data. use can use ``net`` source switch, for example::

$ modeslive --source net --connect localhost 30002 raw
$ modeslive --source net --connect 30005 beast

Example screenshot:

.. image::
:width: 700px

Use the library

.. code:: python

import pyModeS as pms

Common functions

.. code:: python

pms.df(msg) # Downlink Format
pms.icao(msg) # Infer the ICAO address from the message
pms.crc(msg, encode=False) # Perform CRC or generate parity bit

pms.hex2bin(str) # Convert hexadecimal string to binary string
pms.bin2int(str) # Convert binary string to integer
pms.hex2int(str) # Convert hexadecimal string to integer
pms.gray2int(str) # Convert grey code to integer

Core functions for ADS-B decoding

.. code:: python


# Typecode 1-4

# Typecode 5-8 (surface), 9-18 (airborne, barometric height), and 20-22 (airborne, GNSS height)
pms.adsb.position(msg_even, msg_odd, t_even, t_odd, lat_ref=None, lon_ref=None)
pms.adsb.airborne_position(msg_even, msg_odd, t_even, t_odd)
pms.adsb.surface_position(msg_even, msg_odd, t_even, t_odd, lat_ref, lon_ref)

pms.adsb.position_with_ref(msg, lat_ref, lon_ref)
pms.adsb.airborne_position_with_ref(msg, lat_ref, lon_ref)
pms.adsb.surface_position_with_ref(msg, lat_ref, lon_ref)


# Typecode: 19
pms.adsb.velocity(msg) # Handles both surface & airborne messages
pms.adsb.speed_heading(msg) # Handles both surface & airborne messages

Note: When you have a fix position of the aircraft, it is convenient to use `position_with_ref()` method to decode with only one position message (either odd or even). This works with both airborne and surface position messages. But the reference position shall be within 180NM (airborne) or 45NM (surface) of the true position.

Decode altitude replies in DF4 / DF20
.. code:: python

pms.common.altcode(msg) # Downlink format must be 4 or 20

Decode identity replies in DF5 / DF21
.. code:: python

pms.common.idcode(msg) # Downlink format must be 5 or 21

Common Mode-S functions

.. code:: python

pms.icao(msg) # Infer the ICAO address from the message
pms.bds.infer(msg) # Infer the Modes-S BDS register

# Check if BDS is 5,0 or 6,0, give reference speed, track, altitude (from ADS-B)
pms.bds.is50or60(msg, spd_ref, trk_ref, alt_ref)

# Check each BDS explicitly

Mode-S Elementary Surveillance (ELS)

.. code:: python

pms.commb.ovc10(msg) # Overlay capability, BDS 1,0
pms.commb.cap17(msg) # GICB capability, BDS 1,7
pms.commb.cs20(msg) # Callsign, BDS 2,0

Mode-S Enhanced Surveillance (EHS)

.. code:: python

# BDS 4,0
pms.commb.selalt40mcp(msg) # MCP/FCU selected altitude (ft)
pms.commb.selalt40fms(msg) # FMS selected altitude (ft)
pms.commb.p40baro(msg) # Barometric pressure (mb)

# BDS 5,0
pms.commb.roll50(msg) # Roll angle (deg)
pms.commb.trk50(msg) # True track angle (deg)
pms.commb.gs50(msg) # Ground speed (kt)
pms.commb.rtrk50(msg) # Track angle rate (deg/sec)
pms.commb.tas50(msg) # True airspeed (kt)

# BDS 6,0
pms.commb.hdg60(msg) # Magnetic heading (deg)
pms.commb.ias60(msg) # Indicated airspeed (kt)
pms.commb.mach60(msg) # Mach number (-)
pms.commb.vr60baro(msg) # Barometric altitude rate (ft/min)
pms.commb.vr60ins(msg) # Inertial vertical speed (ft/min)

Meteorological reports [Experimental]

To identify BDS 4,4 and 4,5 codes, you must set ``mrar`` argument to ``True`` in the ``infer()`` function:

.. code:: python

pms.bds.infer(msg. mrar=True)

Once the correct MRAR and MHR messages are identified, decode them as follows:

Meteorological routine air report (MRAR)

.. code:: python

# BDS 4,4
pms.commb.wind44(msg) # Wind speed (kt) and direction (true) (deg)
pms.commb.temp44(msg) # Static air temperature (C)
pms.commb.p44(msg) # Average static pressure (hPa)
pms.commb.hum44(msg) # Humidity (%)

Meteorological hazard air report (MHR)

.. code:: python

# BDS 4,5
pms.commb.turb45(msg) # Turbulence level (0-3)
pms.commb.ws45(msg) # Wind shear level (0-3)
pms.commb.mb45(msg) # Microburst level (0-3)
pms.commb.ic45(msg) # Icing level (0-3)
pms.commb.wv45(msg) # Wake vortex level (0-3)
pms.commb.temp45(msg) # Static air temperature (C)
pms.commb.p45(msg) # Average static pressure (hPa)
pms.commb.rh45(msg) # Radio height (ft)

Customize the streaming module
The TCP client module from pyModeS can be re-used to stream and process Mode-S data as you like. You need to re-implement the ``handle_messages()`` function from the ``TcpClient`` class to write your own logic to handle the messages.

Here is an example:

.. code:: python

import pyModeS as pms
from pyModeS.extra.tcpclient import TcpClient

# define your custom class by extending the TcpClient
# - implement your handle_messages() methods
class ADSBClient(TcpClient):
def __init__(self, host, port, rawtype):
super(ADSBClient, self).__init__(host, port, rawtype)

def handle_messages(self, messages):
for msg, ts in messages:
if len(msg) != 28: # wrong data length

df = pms.df(msg)

if df != 17: # not ADSB

if pms.crc(msg) !=0: # CRC fail

icao = pms.adsb.icao(msg)
tc = pms.adsb.typecode(msg)

# TODO: write you magic code here
print(ts, icao, tc, msg)

# run new client, change the host, port, and rawtype if needed
client = ADSBClient(host='', port=30005, rawtype='beast')

Unit test
To perform unit tests, ``pytest`` must be install first.

Build Cython extensions

$ make ext

Run unit tests

$ make test

Clean build files

$ make clean