Understanding Navigation/Auto-Pilot Settings in ADS-B Data

Let's talk about the navigation/auto-pilot settings which are available in ADS-B data. The latest version of SkyAware (for PiAware and FlightFeeder users) now shows this data when it is available.

Today, this data is typically seen from aircraft with newer avionics. It will gradually become more common over time as more aircraft add the capability to transmit this data.
What data is available? There are up to 4 new pieces of data available: selected altitude, selected heading, navigation modes, and QNH. The selected altitude is the altitude to which the aircraft is currently ascending or descending. The selected heading is the direction to which the aircraft is currently turning. Navigation modes are the enabled navigation modes, which are one or more of Auto-Pilot, TCAS, Altitude Hold, Approach, LNAV, and VNAV. The QNH is an atmospheric pressure setting which, when set on an aircraft's altimeter, will cause the altimeter to read altitude above mean sea level within a certain defined region.

Where does this data come from?
The selections for each of the 4 data points are made by the pilot and entered into the aircraft's avionics or Flight Management System (FMS). The ADS-B transponder on the aircraft obtains the data directly from the aircraft's avionics or FMS.

What do the different navigation modes mean?

• Auto-Pilot - the aircraft is following navigation instructions entered in advance by the pilot
• TCAS (Traffic Collision Avoidance System) - this system monitors the airspace around an aircraft for other aircraft and warns pilots of the presence of other aircraft which may present a threat of mid-air collision
• Altitude Hold - this mode maintains a specific altitude by varying the pitch of the aircraft
• Approach - this mode is used to facilitate landing via lateral guidance (GPS/VOR/NDB) in a non-precision approach or via both lateral and vertical guidance in a precision approach (ILS)
• LNAV (Lateral Navigation) - the aircraft is following a procedure prescribed by air traffic control that provides lateral guidance
• VNAV (Vertical Navigation) - the aircraft is following a procedure prescribed by air traffic control that provides vertical guidance

Please note that the usage of "navigation modes" is loosely defined in the ADS-B specifications so exact behavior may vary across aircraft with different transponders or configurations.

We hope this is helpful to you in understanding the ADS-B data that you may be receiving at your site!

For those interested in joining the ADS-B community, FlightAware offers step-by-step instructions to build a PiAware Receiver for under $100.

ADS-B hosts located in areas needing additional coverage might be eligible for a FlightFeeder, a free, prebuilt ADS-B receiver.

FlightAware invites you to join the ADS-B network. You'll become part of a community of aviation hobbyists across the globe and start seeing the skies in a totally different way.