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In case a traffic receiver is connected via FLARM NMEA with the EFB, a conversion of ADS-B aircraft types is necessary. Here is a mapping proposal which has been discussed amongst various stakeholders, including the corresponding transponder settings:

ADSB Description	ADSB Type	OGN/FLARM Type	Garmin Setting	f.u.n.k.e Setting	Dynon/TRIG Setting	Air Avionics VT-01 Setting	Notes
No category information	A-0	0	unknown		Unknown	20
Light (less than 7000 kg, this includes very light aircraft (light sport aircraft) that do not meet the requirements of 14 CFR § 103.1)	A-1	8	light	21	Light	21	600kg Ultralights should use this setting
Small (between 7000 kg and 34000 kg)	A-2	9	small	22	Medium
Large (between 34000 kg to 136000 kg)	A-3	9
High vortex aircraft	A-4	9
Heavy (larger than 136000 kg)	A-5	9

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Sources

• https://github.com/etdey/gdl90
• Garmin® GDL90
• ForeFlight GDL 90 EXTENDED SPECIFICATION

In addition to the original Message ID’s by Garmin, the following extensions are already in use:

• 0x65: Foreflight Message ID (subtype 0): Identification and Capabilities Mask
• 0x65: Foreflight Message ID (subtype 1): AHRS
• Appareo Messages for Stratus (proprietary)
• ForeFlight Messages for Sentry (proprietary)

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GNSS Basics for Collision Avoidance Projects

Sources

• https://www.esri.com/about/newsroom/arcuser/mean-sea-level-gps-geoid

Altitude Definitions

• MSL: altitude above geoid (aka. EGM96 or orthometric altitude or height above mean sea level AMSL or height above geoid HAG)
• HAE: altitude above ellipsoid (aka. WGS84 or geometric or GPS altitude)
• GeoidSep: difference between HAE and MSL
• HAE = MSL + GeoidSep

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Collection of Information about ADS-L

• EASA ADS-L FAQ: https://www.easa.europa.eu/en/the-agency/faqs/automatic-dependent-surveillance-light-ads-l
• SRD860 ADS-L Specification (Issue 1, 20 December 2022): https://www.easa.europa.eu/en/downloads/137503/en
• SRD860 ADS-L Specification (Issue 2, not yet released) which may include:
  • O-Band (869.525 MHz) Low Data Rate (LDR) mode (modulation-level-compatible with PilotAware)
  • O-Band (869.525 MHz) High Data Rate (HDR) mode up to 500mW to upload data from ground infrastructure

preliminary list of ADS-L DIY tracker implementations (transmit and receive)

• https://github.com/pjalocha/ogn-tracker

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Collision Avoidance Information

Radio Protocols

• 868.2 - 868.4 MHz: OGN, FLARM, FANET, ADS-L (25 mW TX power)
  • amongst others, the following essential data is transmitted (and encrypted in case of FLARM):
    • GNSS position and altitude
    • ground speed, sink/climb rate, turn rate, track over ground
    • aircraft ID (or ICAO hex code) and type
• 869.4 – 869.65 MHz: ADS-L, P3I (500 mW TX power)
• typically used for ground stations to re-broadcast traffic from OGN and other sources, potentially weather information in the future