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## Automatic Dependent Surveillance–Broadcast (ADS-B) 

Automatic DGLYPH<df00>pGLYPH<df00>ndGLYPH<df00>nt SurvGLYPH<df00>illancGLYPH<df00>−Broadcast (ADS−B) is a surveillance technology being deployed throughout the NAS to facilitate improvements needed to increase the capacity and efficiency of the NAS, while maintaining safety. ADS-B supports these improvements by providing a higher update rate and enhanced accuracy of surveillance information over the current radar-based surveillance system. In addition, ADS-B enables the expansion of air traffic control (ATC) surveillance services into areas where none existed previously. The ADS-B ground system also provides Traffic Information Services- Broadcast (TIS-B) and Flight Information Services-Broadcast (FIS-B) for use on appropriately equipped aircraft, enhancing the user’s situational awareness (SA) and improving the overall safety of the NAS. 

ThGLYPH<df00> ADS−B systGLYPH<df00>m is composGLYPH<df00>d of aircraft avionics and a ground infrastructure. Onboard avionics determine the position of the aircraft by using the GPS and transmit its position, along with additional information about the aircraft, to ground stations for use by ATC and nearby ADS-B equipped aircraft. 

In thGLYPH<df00> UnitGLYPH<df00>d StatGLYPH<df00>s, ADS−B GLYPH<df00>quippGLYPH<df00>d aircraft GLYPH<df00>xchangGLYPH<df00> information on one of two frequencies: 978 or 1090 MHz. The 1090 MHz frequency is associated with Mode A, C, and S transponder operations. 1090 MHz transponders with integrated ADS−B functionality GLYPH<df00>xtGLYPH<df00>nd thGLYPH<df00> transpondGLYPH<df00>r mGLYPH<df00>ssagGLYPH<df00> sGLYPH<df00>ts with additional ADS−B information. This additional information is known as an “extended squitter” message and referred to as 1090ES. ADS−B GLYPH<df00>quipmGLYPH<df00>nt opGLYPH<df00>rating on 978 MHz is known as the Universal Access Transceiver (UAT). 

## Radar Traffic Advisories 

Radar equipped ATC facilities provide radar assistance to aircraft on instrument flight plans and VFR aircraft provided the aircraft can communicate with the facility and are within radar coverage. This basic service includes safety alerts, traffic advisories, limited vectoring when requested, and sequencing at locations where this procedure has been established. ATC issues traffic advisories based on observed radar targets. The traffic is referenced by azimuth from the aircraft in terms of the 12-hour clock. Also, distance in nautical miles, direction in which the target is moving, and type and altitude of the aircraft, if known, are given. 

An example would be: “Traffic 10 o’clock 5 miles east bound, Cessna 152, 3,000 feet.” The pilot should note that traffic position is based on the aircraft track and that wind correction can affect the clock position at which a pilot locates traffic. This service is not intended to relieve the pilot of the responsibility to see and avoid other aircraft. [Figure 14-44] In addition to basic radar service, terminal radar service 

<img src='content_image/532558.jpg'>

area (TRSA) has been implemented at certain terminal locations. TRSAs are depicted on sectional aeronautical charts and listed in the Chart Supplement U.S. (formerly Airport/Facility Directory). The purpose of this service is to provide separation between all participating VFR aircraft and all IFR aircraft operating within the TRSA. Class C service provides approved separation between IFR and VFR aircraft and sequencing of VFR aircraft to the primary airport. Class B service provides approved separation of aircraft based on IFR, VFR, and/or weight and sequencing of VFR arrivals to the primary airport(s). 

## Wake Turbulence 

All aircraft generate wake turbulence during flight. This disturbance is caused by a pair of counter-rotating vortices trailing from the wingtips. The vortices from larger aircraft pose problems to encountering aircraft. The wake of these aircraft can impose rolling moments exceeding the roll- control authority of the encountering aircraft. Also, the turbulence generated within the vortices can damage aircraft components and equipment if encountered at close range. For this reason, a pilot must envision the location of the vortex wake and adjust the flight path accordingly. 

## Vortex Generation 

Lift is generated by the creation of a pressure differential over the wing surface. The lowest pressure occurs over the upper wing surface and the highest pressure under the wing. This pressure differential triggers the rollup of the airflow aft of the wing resulting in swirling air masses trailing downstream of the wingtips. After the rollup is completed, the wake consists of two counter rotating cylindrical vortices. Most of the energy lies within a few feet of the center of each vortex. [Figure 14-45] 

