Definition
Automatic Dependent Surveillance — Broadcast (ADS-B) is a cooperative surveillance system in which an aircraft autonomously broadcasts its own state vector — position derived from GNSS, barometric altitude, groundspeed, vertical rate, and aircraft identification — to ATC ground stations and to other aircraft within radio range. The word "dependent" distinguishes it from independent radar surveillance: ADS-B depends on the aircraft's onboard navigation system to determine position, which is then broadcast rather than interrogated. "Broadcast" distinguishes it from selective interrogation systems like SSR Mode S: the ADS-B transmission is one-way and continuous, with no interrogation required.
In the United States, ADS-B Out carriage and operation is mandatory under 14 CFR §91.225, effective January 1, 2020. The rule requires ADS-B Out in Class A airspace; Class B airspace; Class C airspace; Class E airspace at and above 10,000 ft MSL (excluding airspace at and below 2,500 ft AGL); within 30 NM of Class B primary airports (the Mode C veil); and above the ceiling and within the lateral boundaries of Class B or Class C airspace up to 10,000 ft MSL. The performance standards for the ADS-B Out signal are defined in §91.227, which requires a 1090 MHz Extended Squitter (1090ES) transmitter or a Universal Access Transceiver (UAT) operating on 978 MHz. The 1090ES standard conforms to RTCA DO-260B; UAT conforms to RTCA DO-282B. 1090ES is the globally compatible standard, used by all transport-category and most turbine aircraft worldwide. UAT 978 MHz is a US-only variant available only below 18,000 ft MSL — it is not accepted outside the United States and is therefore not suitable for aircraft that will operate internationally.
The position source feeding ADS-B Out must be a GNSS receiver compliant with the navigation accuracy category position (NACp) requirements of §91.227: specifically, NACp ≥ 8 (95% containment radius ≤ 0.05 NM) and navigation integrity category (NIC) ≥ 7, achievable with a WAAS-capable GPS receiver. Non-WAAS GPS or barometric-only altitude sourcing does not meet the standard. For Mode S transponders providing 1090ES ADS-B Out, the avionics must be at least Mode S Level 2 with extended squitter activated — many older Mode S transponders without extended squitter capability require either a software update or a new transponder to comply.
In European Union airspace, ADS-B Out is required under Commission Implementing Regulation (EU) No 1207/2011 as amended, with a mandate date of December 7, 2020 for fixed-wing aircraft above 5,700 kg MTOM or with TAS capability above 250 kt, operating under IFR/RVFR in Class A–C airspace. EASA AMC1 SPA.NAV.105 and related guidance address ADSB-based separation applications under SESAR. Lighter aircraft and helicopters follow a phased rollout. The European standard requires 1090ES only — UAT is not an accepted European standard.
ADS-B In is the complementary receive-only function: an aircraft equipped with ADS-B In receives broadcasts from other ADS-B Out-equipped aircraft (direct air-to-air) and from ATC ground stations re-broadcasting Traffic Information Service — Broadcast (TIS-B) and Flight Information Service — Broadcast (FIS-B). FIS-B provides graphical weather (METARs, TAFs, PIREPs, AIRMETs, SIGMETs, NOTAMs) directly to the cockpit display via UAT datalink. ADS-B In is not mandated by either FAA or EASA but is increasingly standard in glass-cockpit general aviation aircraft, providing NEXRAD weather, traffic, and TFR overlays on EFB applications.
Why It Matters for Flight Schools
For flight schools, the ADS-B Out mandate creates an equipment compliance obligation that affects every aircraft in the training fleet. Aircraft without compliant ADS-B Out transmitters are legally prohibited from operating in the airspace classes listed in §91.225, which in practice means they cannot fly into or near any major airport in the US or EU. Schools that have not yet upgraded their entire fleet — particularly schools with older Cessna 172s or Piper Warriors with vintage avionics — face routing restrictions that limit student cross-country options and may prevent solo students from accessing certain practice areas near Class B or C airports.
Beyond the equipment obligation, ADS-B is increasingly relevant to training because it underpins the surveillance infrastructure students will encounter throughout their careers. Understanding ADS-B Out versus In, 1090ES versus UAT, and the NACp/NIC position quality requirements is explicitly tested on FAA knowledge exams and discussed in ACS requirements. Schools with ADS-B In-equipped training aircraft can use real-time TIS-B traffic and FIS-B weather overlays as instructional tools during flights, making airspace situational awareness training more concrete and realistic.
How Aviatize Handles This
Aviatize's maintenance control module tracks each aircraft's avionics equipment configuration, including ADS-B Out transponder type (1090ES or UAT), compliance documentation (STC or original equipment), and the results of required performance monitoring checks. When an aircraft's ADS-B Out transmitter generates a position quality failure flag from FAA ADS-B Performance Reports (available from the FAA's surveillance and broadcast services), maintenance staff can log the discrepancy and the aircraft can be flagged as restricted from airspace requiring ADS-B Out until the issue is resolved.
For dispatch, Aviatize's smart planning and booking module validates each booking's planned airspace against the assigned aircraft's ADS-B Out status. A student cross-country booking that routes through Class B airspace on an aircraft without a compliant ADS-B Out installation is flagged before it reaches the schedule, preventing a regulatory violation from being dispatched. This validation is particularly important for schools with mixed fleets containing both ADS-B-equipped and legacy airframes.