ADS-B

§01What is ADS-B?

ICAO’s air traffic management procedures describe ADS-B as a means by which aircraft, aerodrome vehicles and other objects can automatically transmit and/or receive data.¹Source 1 · SKYbraryAutomatic Dependent Surveillance – Broadcast (ADS-B)skybrary.aero The name spells out how it works. It is automatic because no pilot or controller has to trigger it. It is dependent because it relies on the aircraft’s own navigation source. It is surveillance because it tells others where the aircraft is. And it is a broadcast: one-to-many, with no interrogation and no addressee.

ADS-B Out is the transmitting side; ground stations use it for surveillance. ADS-B In is an onboard receiver and display that builds a traffic picture for the crew.¹Source 1 · SKYbraryAutomatic Dependent Surveillance – Broadcast (ADS-B)skybrary.aero Two data links carry it. The 1090 MHz extended squitter, built on Mode S, is used worldwide, and the 978 MHz Universal Access Transceiver (UAT) is used in the United States.¹Source 1 · SKYbraryAutomatic Dependent Surveillance – Broadcast (ADS-B)skybrary.aero²Source 2 · Legal Information Institute, Cornell Law School14 CFR § 91.225 – ADS-B Out equipment and uselaw.cornell.edu

§02What is inside an ADS-B message?

A 1090 MHz ADS-B frame is 112 bits long. It holds a 5-bit downlink format (17 for civil ADS-B), the aircraft’s 24-bit ICAO address, a 56-bit payload and 24 bits of parity. A type code inside the payload tells you what the payload carries: identification and callsign, surface or airborne position, velocity, or operational status. With ADS-B version 2, airborne position and velocity are broadcast at about 2 Hz.³Source 3 · Junzi Sun, mode-s.orgThe 1090 Megahertz Riddle: ADS-B basicsmode-s.org

§03Example: one decoded position

12345678910111213{
  "icao24": "abc123",
  "callsign": "KMO123",
  "lat": 50.8412,
  "lon": 4.3721,
  "baro_alt_ft": 36000,
  "ground_speed_kt": 452,
  "track_deg": 118,
  "squawk": "4712",
  "nacp": 10,
  "nic": 8,
  "position_source": "adsb"
}

The aircraft is fictional. What matters is the shape: one row per aircraft per moment, keyed by icao24, with the squawk code and the self-reported accuracy indicators (NACp, NIC) kept next to the position. Those indicators are what make GNSS interference visible in open data.

§04Common misconceptions

• “ADS-B is radar.” It is not. Radar measures the aircraft; ADS-B is the aircraft describing itself. If its navigation source is degraded, the broadcast position is degraded too.
• “Everything flying broadcasts ADS-B.” Mandates cover specific airspace. In the US, 14 CFR 91.225 has required ADS-B Out since January 1, 2020 in Class A, B and C airspace and in Class E airspace at and above 10,000 ft MSL over the contiguous states, with carve-outs for aircraft certificated without an electrical system, such as gliders and balloons.²Source 2 · Legal Information Institute, Cornell Law School14 CFR § 91.225 – ADS-B Out equipment and uselaw.cornell.edu Outside those rules, coverage is partial.
• “Messages are verified.” The protocol has no built-in security measures, which researchers have studied for years.⁴Source 4 · Strohmeier, Lenders, Martinovic, arXiv, 2013On the Security of the Automatic Dependent Surveillance-Broadcast Protocolarxiv.org Treat every field as a claim to check.

§05How Kimo uses ADS-B

Kimo Defense Intelligence ingests ADS-B from your own receivers or open feeds such as OpenSky through the ADS-B connector. It normalizes the data into a tracks model, tags each point with its source (ADS-B or MLAT) and freshness, and drives the live map in Airspace. The Airspace watch template sets this up in under an hour, and the ADS-B ingestion guide covers each step. All aircraft shown in Kimo demos are simulated.

§06Related terms

• Mode S: the transponder system that ADS-B on 1090 MHz is built on.
• Multilateration (MLAT): an independent position computed from signal timing.
• Squawk code: the four-digit identity code, including emergency codes.
• Data fusion: combining ADS-B with other sources into one track.