Version 2 API Fields

This file contains readsb 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: bitfield for certain database flags use a bitwise AND (&). Check the documentation for your programming language.
      • military = dbFlags & 1;
      • interesting = dbFlags & 2;
      • PIA = dbFlags & 4;
      • LADD = dbFlags & 8;
    • 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
    • rr_lat, rr_lon: If no ADS-B or MLAT position available, a rough estimated position for the aircraft based on the receiver’s coordinates.
    • 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.

Supplementary Data Field

  • lastPosition: {lat, lon, nic, rc, seen_pos} when the regular lat and lon are older than 60 seconds they are no longer considered valid, this will provide the last position and show the age for the last position. Aircraft will only be in the aircraft json if a position has been received in the last 60 seconds or if any message has been received in the last 30 seconds.

Trace File Fields

    icao: "0123ac", // hex id of the aircraft
    timestamp: 1609275898.495, // unix timestamp in seconds since epoch (1970)
    trace: [
        [ seconds after timestamp,
            altitude in ft or "ground" or null,
            ground speed in knots or null,
            track in degrees or null,
            flags as a bitfield: (use bitwise and to extract data)
                (flags & 1 > 0): position is stale (no position received for 20 seconds before this one)
                (flags & 2 > 0): start of a new leg (tries to detect a separation point between landing and takeoff that separates fligths)
                (flags & 4 > 0): vertical rate is geometric and not barometric
                (flags & 8 > 0): altitude is geometric and not barometric
            vertical rate in fpm or null,
            aircraft object with extra details or null
        [next entry like the one before],
        [next entry like the one before],


    "desc":"Bombardier Learjet 31 A",
    "timestamp": 1609275898.495,
    {"type":"adsb_icao","flight":"YV3382  ","alt_geom":-75,"track":0.00,"baro_rate":0,"squawk":"1604","emergency":"none","category":"A1","nic":8,"rc":186,"version":2,"nic_baro":1,"nac_p":10,"nac_v":2,"sil":3,"sil_type":"perhour","gva":2,"sda":2,"alert":0,"spi":0}],