Fields and units

Each aircraft is a record in readsb’s aircraft.json format (readsb docs), the same as tar1090 and adsb.lol. Fields are missing when the aircraft doesn’t transmit them. The main ones:

Field	Meaning	Unit
hex	24-bit ICAO address; a leading ~ marks a non-ICAO address (e.g. TIS-B)	hexadecimal
flight	callsign, padded with spaces to 8 characters: trim() it
r	registration, from the aircraft database
t	ICAO type code (e.g. A320), from the aircraft database
dbFlags	bit values: 1 military, 2 interesting, 4 PIA, 8 LADD	bitmask
lat, lon	position	decimal degrees
alt_baro	barometric altitude, or the string "ground" when on the ground	feet
alt_geom	geometric (GNSS) altitude	feet
gs	ground speed	knots
track	true track	degrees
baro_rate	vertical rate	feet/minute
squawk	transponder code, 4 digits
category	emitter category (e.g. A3)
type	position source: adsb_icao, mlat, tisb_icao, adsr_icao…
seen	seconds since the last message	seconds
seen_pos	seconds since the last position	seconds
mlat	the fields derived from multilateration	list

For the other fields (ias, mach, nav_altitude_mcp, rssi…), see readsb’s documentation.

Good to know

• alt_baro can be a string. Check its type before doing maths: "ground" means on the ground.
• Aviation units: feet, knots and feet per minute. The request radius, on the other hand, is in kilometres.
• Freshness: positions older than about 60 seconds are not returned. seen_pos tells you how recent the one you see is.
• Times: now is in Unix seconds (UTC); seen and seen_pos are relative to it.
• Registration and type are there for about 99% of aircraft. They are missing for new addresses or ones not in the database.
• Not included: the route (departure and arrival airports), the operating airline and photos.
• type: mlat: the position comes from our multilateration, not from the aircraft. See How MLAT works.