ADS-B Data Field Explanations

The output is list of recently seen aircraft.

Status information:

  • msg: Shows if there is an error, default is “No error”.
  • now: The time this file was generated, in seconds since Jan 1 1970 00:00:00 GMT (the Unix epoch)
  • total: Total aircraft returned.
  • ctime: The time this file was cached, in seconds since Jan 1 1970 00:00:00 GMT (the Unix epoch).
  • ptime: The server processing time this request required in milliseconds.


For each aircraft object, the following are shown if available.

  • now: the time this file was generated, in seconds since Jan 1 1970 00:00:00 GMT (the Unix epoch).
  • messages: the total number of Mode S messages processed since readsb started.
  • aircraft: an array of JSON objects, one per known aircraft. Each aircraft has the following keys. Keys will be omitted if data is not available.
    • hex: the 24-bit ICAO identifier of the aircraft, as 6 hex digits. The identifier may start with ‘~’, this means that the address is a non-ICAO address (e.g. from TIS-B).
    • type: type of underlying messages / best source of current data for this position / aircraft: (the following list is in order of which data is preferentially used)
      • adsb_icao: messages from a Mode S or ADS-B transponder, using a 24-bit ICAO address
      • adsb_icao_nt: messages from an ADS-B equipped “non-transponder” emitter e.g. a ground vehicle, using a 24-bit ICAO address
      • adsr_icao: rebroadcast of ADS-B messages originally sent via another data link e.g. UAT, using a 24-bit ICAO address
      • tisb_icao: traffic information about a non-ADS-B target identified by a 24-bit ICAO address, e.g. a Mode S target tracked by secondary radar
      • adsc: ADS-C (received by monitoring satellite downlinks)
      • mlat: MLAT, position calculated arrival time differences using multiple receivers, outliers and varying accuracy is expected.
      • other: miscellaneous data received via Basestation / SBS format, quality / source is unknown.
      • mode_s: ModeS data from the planes transponder (no position transmitted)
      • adsb_other: messages from an ADS-B transponder using a non-ICAO address, e.g. anonymized address
      • adsr_other: rebroadcast of ADS-B messages originally sent via another data link e.g. UAT, using a non-ICAO address
      • tisb_other: traffic information about a non-ADS-B target using a non-ICAO address
      • tisb_trackfile: traffic information about a non-ADS-B target using a track/file identifier, typically from primary or Mode A/C radar
    • flight: callsign, the flight name or aircraft registration as 8 chars (
    • r: aircraft registration pulled from database
    • t: aircraft type pulled from database
    • dbFlags: military and interesting bitwise & pulled from database
      • 1: mil
      • 2: interesting
      • 3: both
    • alt_baro: the aircraft barometric altitude in feet
    • alt_geom: geometric (GNSS / INS) altitude in feet referenced to the WGS84 ellipsoid
    • gs: ground speed in knots
    • ias: indicated air speed in knots
    • tas: true air speed in knots
    • mach: Mach number
    • track: true track over ground in degrees (0-359)
    • track_rate: Rate of change of track, degrees/second
    • roll: Roll, degrees, negative is left roll
    • mag_heading: Heading, degrees clockwise from magnetic north
    • true_heading: Heading, degrees clockwise from true north (usually only transmitted on ground, in the air usually derived from the magnetic heading using magnetic model WMM2020)
    • baro_rate: Rate of change of barometric altitude, feet/minute
    • geom_rate: Rate of change of geometric (GNSS / INS) altitude, feet/minute
    • squawk: Mode A code (Squawk), encoded as 4 octal digits
    • emergency: ADS-B emergency/priority status, a superset of the 7×00 squawks (
    • category: emitter category to identify particular aircraft or vehicle classes (values A0 – D7) (

A- = Unspecified powered aircraft
A1 = Light (< 15 500 lbs.)
A2 = Small (15 500 to 75 000 lbs.)
A3 = Large (75 000 to 300 000 lbs.)
A4 = High Vortex Large(aircraft such as B-757)
A5 = Heavy (> 300 000 lbs.)
A6 = High Performance ( > 5 g acceleration and > 400kts)
A7 = Rotorcraft
B- = Unspecified unpowered aircraft or UAV or spacecraft
B1 = Glider/sailplane
B2 = Lighter-than-Air
B3 = Parachutist/Skydiver
B4 = Ultralight/hang-glider/paraglider
B5 = Reserved
B6 = Unmanned Aerial Vehicle
B7 = Space/Trans-atmospheric vehicle
C- = Unspecified ground installation or vehicle
C1 = Surface Vehicle – Emergency Vehicle
C2 = Surface Vehicle – Service Vehicle
C3 = Fixed Ground or Tethered Obstruction
C4 = Cluster Obstacle
C5 = Line Obstacle
C6-C7 = Reserved
D0 = No ADS-B Emitter Category Information
D1-D7 = Reserved

    • nav_qnh: altimeter setting (QFE or QNH/QNE), hPa
    • nav_altitude_mcp: selected altitude from the Mode Control Panel / Flight Control Unit (MCP/FCU) or equivalent equipment
    • nav_altitude_fms: selected altitude from the Flight Manaagement System (FMS) (
    • nav_heading: selected heading (True or Magnetic is not defined in DO-260B, mostly Magnetic as that is the de facto standard) (
    • nav_modes: set of engaged automation modes: ‘autopilot’, ‘vnav’, ‘althold’, ‘approach’, ‘lnav’, ‘tcas’
    • lat, lon: the aircraft position in decimal degrees
    • nic: Navigation Integrity Category (
    • rc: Radius of Containment, meters; a measure of position integrity derived from NIC & supplementary bits. (, Table 2-69)
    • seen_pos: how long ago (in seconds before “now”) the position was last updated
    • track: true track over ground in degrees (0-359)
    • version: ADS-B Version Number 0, 1, 2 (3-7 are reserved) (
    • nic_baro: Navigation Integrity Category for Barometric Altitude (
    • nac_p: Navigation Accuracy for Position (
    • nac_v: Navigation Accuracy for Velocity (
    • sil: Source Integity Level (
    • sil_type: interpretation of SIL: unknown, perhour, persample
    • gva: Geometric Vertical Accuracy (
    • sda: System Design Assurance (
    • mlat: list of fields derived from MLAT data
    • tisb: list of fields derived from TIS-B data
    • messages: total number of Mode S messages received from this aircraft
    • seen: how long ago (in seconds before “now”) a message was last received from this aircraft
    • rssi: recent average RSSI (signal power), in dbFS; this will always be negative.
    • alert: Flight status alert bit (
    • spi: Flight status special position identification bit (
    • wd, ws: wind direction, wind speed: calculated from ground track, true heading, true airspeed and ground speed
    • oat, tat: outer air temperate, total air temperature: calculated from mach number and true airspeed (typically somewhat inaccurate at lower altitudes / mach numbers below 0.5)

Section references ( refer to DO-260B.