Figure 5-47. Example of a multi-function display (MFD). usable pilot information. The accuracy of the system is now  determined by the accuracy of the navigation system, not  measurement errors. Furthermore the accuracy is unaffected  by the range to the aircraft as in the case of radar. With radar,  detecting aircraft speed changes require tracking the data and  changes can only be detected over a period of several position  updates. With ADS-B, speed changes are broadcast almost  instantaneously and received by properly equipped aircraft.  Additionally, other information can be obtained by properly  equipped aircraft to include notices to airmen (NOTAM),  weather, etc.  [Figures 5-49  and  5-50]  At the present time,  ADS-B is predominantly available along the east coast of  the United States where it is matured. A radio altimeter, commonly referred to as a radar altimeter,  is a system used for accurately measuring and displaying the  height above the terrain directly beneath the aircraft. It sends  a signal to the ground and processes the timed information.  Its primary application is to provide accurate absolute altitude  information to the pilot during approach and landing. In  The Traffic Information Service (TIS) is a ground-based  service providing information to the flight deck via data  link using the S-mode transponder and altitude encoder. TIS  improves the safety and efficiency of “see and avoid” flight  through an automatic display that informs the pilot of nearby  traffic. The display can show location, direction, altitude  and the climb/descent trend of other transponder-equipped  aircraft. TIS provides estimated position, altitude, altitude  A typical system consists of a receiver-transmitter (RT)  unit, antenna(s) for receiving and transmitting the signal,  and an indicator.  [Figure 5-51]  Category II and III precision  approach procedures require the use of a radar altimeter and  specify the exact minimum height above the terrain as a  decision height (DH) or radio altitude (RA). advanced aircraft today, the radar altimeter also provides its  information to other onboard systems such as the autopilot  and flight directors while they are in the glideslope capture  mode below 200-300 feet above ground level (AGL). Traffic Advisory Systems  Traffic Information System  Safety Systems Radio Altimeters 5-29