Python ADS-B/Mode-S Decoder

Mode-S ADS-B EHS decoding, ads-b, adsb, aircraft, ehs, mode-s, python, tracking
pip install pyModeS==2.1


The Python ADS-B/Mode-S Decoder

Python library for ADS-B/Mode-S message decoding. Supported Downlink Formats (DF) are:

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 replies

  • BDS 1,0: Data link capability report
  • BDS 1,7: Common usage GICB capability report
  • BDS 2,0: Aircraft identification
  • BDS 2,1: Aircraft and airline registration markings
  • BDS 3,0: ACAS active resolution advisory
  • BDS 4,0: Selected vertical intention
  • BDS 4,4: Meteorological routine air report
  • BDS 5,0: Track and turn report
  • BDS 5,3: Air-referenced state vector
  • BDS 6,0: Heading and speed report

DF4 / DF20: Altitude code

DF5 / DF21: Identity code (squawk code)

Detailed manual on Mode-S decoding is published by the author, at:

New features in v2.0

  • New structure of the libraries
  • ADS-B and Comm-B data streaming
  • Active aircraft viewing (terminal curses)
  • Improved BDS identification
  • Optimizing decoding speed

Source code

Checkout and contribute to this open-source project at:

API documentation at:


To install latest version from the GitHub:

pip install git+

To install the stable version (2.0) from pip:

pip install pyModeS

Live view traffic (modeslive)

Supports Mode-S Beast and AVR raw stream

modeslive --server [server_address] --port [tcp_port] --rawtype [beast,avr,skysense] --latlon [lat] [lon]  --dumpto [folder]

  -h, --help           show this help message and exit
  --server SERVER      server address or IP
  --port PORT          raw data port
  --rawtype RAWTYPE    beast, avr or skysense
  --latlon LAT LON     receiver position
  --show-uncertainty   display uncertaint values, default off
  --dumpto             folder to dump decoded output

If you have a RTL-SDR receiver or Mode-S Beast, use modesmixer2 ( to create raw beast TCP stream:

$ modesmixer2 --inSeriel port[:speed[:flow_control]] --outServer beast:[tcp_port]

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 interger

Core functions for ADS-B decoding


# Typecode 1-4

# Typecode 5-8 (surface), 9-18 (airborne, barometric height), and 9-18 (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 with in 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.alt40mcp(msg)   # MCP/FCU selected altitude (ft)
pms.commb.alt40fms(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)


To perform unit tests. First install tox through pip, Then, run the following commands:

$ tox