Open the Attached PDF for more information on TIS-B

The No TIS-B indicator is not an error message, just an indication that we are not receiving service to the hockey puck surrounding our aircraft from the ground. We don't suppress any data due to the No TIS-B indication so it is not surprising they are seeing traffic targets even with the indicator displayed.

·         We show the No TIS-B indicator if:

·        

o   We have not seen a service status ground uplink message with our ICAO address for more than 40 seconds

o   A service status ground uplink message indicates the ownship ICAO address is not receiving TIS-B/ADS-R service and there are no other ground stations currently providing TIS-B/ADS-R service

o   The only ground station providing service uses a site id of 0 (site id of 0 is reserved for non tis-b station)

What is the No TIS-B Indicator?

ADS-R and TIS-B are transmitted from ground stations, and while the messages themselves are broadcast, only the targets within 30 nm and 3500 ft  of a "Participating" Aircraft are transmitted.  That cylinder surrounding a participating aircraft is affectionately known as the ADS-B hockey puck.  To be a "participating aircraft", you must be equipped with compliant ADS-B out and your GPS position quality metrics must be above a threshold set by the FAA.

The No TIS-B indicator is displayed to indicate the ground is likely not providing the intruders for our hockey puck.  Even if you are not receiving service to your hockey puck, you will still see all on-frequency (978 for the Skytrax) targets as well as all ADS-R and TIS-B targets for the hockey pucks of other participating aircraft.  If you were a non-participating aircraft flying right next to a participating aircraft with identical ADS-B in capability, you would effectively receive all the targets of interest even without being "in-service".  

The reasons for the No TIS-B indicator:

• ​Really no ground station providing service to our Hockey Puck
  • If the aircraft does not have ADS-B out, the ground will not provide service.
  • If the aircraft GPS quality metrics are too low (see the FAA's notice here: Changes to TIS-B Service)
  • If the aircraft is too low/out of range of an ADS-B ground station receiver
    • ​Note: The transmit power from the ground is higher than airborne transmitters so you may receive FIS-B weather from the transmit side of the ground station even if your signal is too faint to be heard by the ground station.
    • Below about 1500 ft AGL, you will not be heard by the ground stations in most areas
• ​There is a ground station providing service, but we cannot detect it
  • If the ICAO in the ADS-B out or in device is misconfigured, we cannot detect when the ground is providing service as the service status is provided as a list of ICAO addresses
  • ADS-B is transmitted over a lossy channel and it is expected some number of messages will be dropped, it is possible to drop enough Service Status updates to trigger an annunciation even though the aircraft is being serviced
    • This would likely manifest as the No TIS-B indication appearing intermittently