Pilot's Guide to Avionics 2011-2012 - 62

INS AND OUTS OF ADS-B
Continued from page 61

You can wait and see; fit the update into a panel makeover or other upgrade . But, if you’re already lacking weather and traffic – or would like more or better – consider going all in and adopting ADS-B In at some point, as well . Once you do, you’ll gain benefits from the system and not merely contribute Out benefits to the FAA and, in the process, enhance your hazard-awareness several levels . And here's a tip worth remembering: When the time comes, replace a failed Mode A/C transponder with a modern Mode S model capable – or upgradeable – to deliver ADS-B Out . You’ll satisfy the regulatory requirement at a competitive price .

ADS-B Out Equipment Requirements:
WAAS GPS or other performance-compliant navigator – stand-alone (blind), integral to a single-box ADS-B system or a panel-mounted navigator. ADS-B Out Transmitter, either a 978 MHz ADS-B standalone transmitter or UAT; or 1090ES Unit, stand-alone or an ADS-B Capable Mode S Transponder and an antenna.

ADS-B In Equipment Requirements:
(in addition to Out hardware) 978 MHz ADS-B Receiver or 978 UAT to receive the Out signals of other aircraft, as well as FIS-B and TIS-B data; or 1090ES also able to receive TIS-B and a display screen of some type to show FIS-B and TIS-B images and text; can be stand-alone, MFD or the screen of a GPS navigator.

The data an aircraft broadcasts includes highly accurate position information supplied by a navigation source – either a performance-qualified RNAV or inertial-nav source or the most-popular method which this article focuses on, WAAS GPS – connected to the aircraft’s ADS-B Out transmitter; the GPS data package also includes speed and direction of flight . The aircraft’s altitude source must be the same as the altitude source of the encoder, and it is important that the aircraft's ADS-B system and tansponder/encoder system report the same altitude . Finally, the aircraft’s ADS-B Out system updates the data broadcast hundreds of times per minute . Receiving these data broadcasts are ground repeater stations connected to controllers via ground-communications computer processors; those stations already number more than 300, with about 800 total planned . So, how does this all differ from today’s ATC surveillance technologies? Today, when a surveillance radar beam sweeps – or “pings” – an aircraft transponder, the transponder “replies” by broadcasting one of 4,009 discrete four-digit codes, along with altitude data derived by an encoder attached to the transponder . The computers take the transponder “squawks” and process them into targets on controllers’ screens showing the aircraft’s code, its position, altitude and a flight vector . Flying the en route system, the computers update position reports every couple of minutes; radar in terminal areas updates the screen image several times a minute . And, the data lacks anything approaching the precision of the ADS-B Out . Not only is the data updated multiple times a second, the GPS-provided data broadcast incorporates information corrected by the wide-area augmentation system, and WAAS delivers position accuracy of less than 50 feet laterally, under 15 feet vertically and within a fraction of a knot . ADS-B Out versus ADS-B In Two related technologies share a system – that’s ADS-B Out and ADS-B In . Where ADS-B In comes into play – and holds appeal to many – is a pair of “free” (excise-taxpayer funded) services which require additional equipment beyond that required to meet the mandate for ADS-B Out . The repeater aspect of the ground stations involves re-broadcasting the two products: the traffic information service-broadcast (TIS-B) and the flight information
Continued on page 64…

The Basics Here is a quick refresher on ADS-B – what it is, what it does, equipment needed, why the FAA wants the system and how pilots can benefit from components of the system, individually and as a whole . Let’s start by revisiting the basics of this technology . Automatic dependent surveillance-broadcast . The name itself nicely describes what’s happening . ADS-B Out automatically broadcasts a package of data from the aircraft, data which FAA air traffic service controllers depend on to maintain aircraft surveillance .

- 62 -

Pilot's Guide to Avionics 2011-2012

Table of Contents for the Digital Edition of Pilot's Guide to Avionics 2011-2012