TIS-B Explained: Traffic Information System Broadcast for NextGen
TIS-B, or Traffic Information System-Broadcast, is a data broadcasting service that allows aircraft operators to receive traffic information in near-real time. Along with its partner system FIS-B, TIS-B is being offered at no cost to ADS-B users as part of the FAA's Next Generation Air Transportation System (NextGen).
TIS-B is a traffic reporting system that uses ADS-B ground stations and radar data to transmit aircraft position data to aircraft cockpit displays.
In essence, TIS-B will allow pilots in the cockpit to see what the air traffic controller sees - other aircraft, along with those aircraft's altitudes, direction, and speed vectors on their aircraft's display screen.
How TIS-B Works:
TIS-B data is transmitted from a ground station to all ADS-B equipped aircraft, whether the aircraft uses a 1090 MHz ES link or a 978 MHz UAT data link. The traffic information is taken from radar sensors on ground stations and broadcast through ADS-B data links to aircraft.
The aircraft's ADS-B receiver will interpret the data and display it onto a screen in the cockpit. The actual interface on which TIS-B will be displayed will vary with the various different types of avionics on the market today, but it will most likely be incorporated into a flight management system or an electronic flight bag (EFB) to some standard degree. Typically, traffic is displayed as a small triangle with a line showing the aircraft's direction and speed, and the altitude readout somewhere next to the aircraft's triangle icon.
Pilots who want to receive TIS-B information on their airplanes must be equipped with a compatible ADS-B transmitter (ADS-B Out) and receiver (ADS-B In), or a transceiver (both). ADS-B requires a WAAS-enabled GPS receiver and a transponder when one is not already included with the ASD-B unit.
A compatible cockpit display (CDIT) is also needed to display the traffic in graphic format.
There are a few limitations that exist with TIS-B that pilots should be aware of when flying.
- TIS-B is advisory in nature
- TIS-B is only available within the service areas configured for TIS-B and while within the coverage area of at least one ATC radar unit.
- Radar lags behind ADS-B when it comes to updates. Since ADS-B updates about once per second and radar updates every three to 13 seconds, it's possible that aircraft pilots might see a target of their own aircraft when maneuvering before ATC is aware of the same target.
- TIS-B uses both ADS-B data and radar data. At times, the messages received from ADS-B and radar can be slightly different from each other and interpreted inaccurately. This can result in duplicate traffic figures on the display.
- Aircraft must be equipped with an operable transponder to appear as a target on a display.
The FAA warns pilots that TIS-B is not a replacement for standard traffic separation and avoidance techniques. Unlike TCAS, TIS-B does not give traffic collision guidance and traffic avoidance maneuvers are not authorized. Pilots should remember that traffic avoidance maneuvers are not authorized as a response to TIS-B displays, and ATC violations may occur in the event that a pilot deviates from his or her assigned instructions.