The Python ADS-B/Mode-S Decoder

PyModeS is a Python library designed to decode Mode-S (including ADS-B) message. 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

# development version
pip install git+

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

Advanced installation (using c modules)

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

git clone
cd pyModeS
make ext
make install

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 plugged to the computer, you can connect it with rtlsdr source switch, shown as follows:

$ 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:

Use the library

import pyModeS as pms

Common functions

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


# 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

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

Decode identity replies in DF5 / DF21

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

Common Mode-S functions

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)

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)

# 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 routine air report (MRAR) [Experimental]

# 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) [Experimental]

# 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:

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

Indices and tables