ADS-B In: Take Advantage
By Dave Graham, FreeFlight Systems' NextGen Customer Support Manager
The 2020 mandate for ADS-B isn't going away. It's time to get serious about a solution. Multiple avionics manufacturers have ADS-B solutions looking for a home in your aircraft. Avionics shops are seeing a spike in demand and a majority are reporting backlogs, some as long as twelve months. Prices for ADS-B systems are decreasing while installation costs are increasing. With a myriad of options available, what should be considered in order to obtain all the benefits of having ADS-B-In?
Consider your aircraft and where you fly. An ADS-B-In solution for a relatively new Daher Socata TBM 850 is going to be very different from an ADS-B-In system for the Piper SuperCub you learned to fly on. For the first time, ADS-B-In will allow pilots to have the same traffic and weather picture that air traffic controllers see. Having a display is a precursor to making use of the great information that ADS-B-In provides. Cockpit displays come in many varieties; GPS navigators, EFIS screens, HUDs and now more and more ever, the humble iPad. When selecting an ADS-B-In system determining how that information is displayed in your cockpit is essential.
1090 or 978? 1090 MHz is the frequency a standard Mode A/C transponder uses for transmission. The technology was invented in the 1950's and has steadily expanded since then. 1090 MHz works in all airspace, above and below 18,000 ft. Having been around since radar was invented, the 1090 MHz frequency band facilitates Mode A, Mode C, Mode S, Mode S-ES, TCAS I and TCAS II. In other words, the 1090 MHz band is congested. Transmissions and interrogations are unsynchronized. In a busy terminal area the band can quickly become overloaded. With the 1090 MHz band, bandwidth availability for carrying more information is limited. This is why 1090 MHz receiver provides traffic information only, no weather.
Enter the Universal Access Transceiver (UAT). Operating on the 978 MHz band, UATs overcome the bandwidth limitations and restrictions of 1090 MHz. Developed in the early 2000's, this technology synchronizes transmission and receiving to UTC seconds. Being a more modern technology, it uses much less power and transmits and receives over a much greater distance. Even with the transmission of weather and traffic information, only about 10% of the available bandwidth is being used. UAT's can facilitate future requirements (example: UAVs) that are currently envisaged in a post mandate world.
Getting a true traffic picture - In relies on Out: To receive the full traffic picture, an aircraft has to be what's called a "Participant Aircraft." A participant aircraft transmits its position on one of the two ADS-B frequencies. When a ground station receives that message, it re-broadcasts the traffic on the other frequency, and adds the non-ADS-B traffic seen by radar. Part of the message a participant aircraft transmits is whether there is an ADS-B receiver on board, and its type. Ground stations are thus able to determine what traffic targets to send to the participant aircraft.
What about portable options? Portable ADS-B receivers using WiFi or Bluetooth talk to most available tablet flight planning applications but can only be used for ADS-B-In, and aren't compliant for ADS-B-Out. If your aircraft already has an ADS-B Out only system, the ADS-B Out transmitter may not be informing the ground stations that a receiver is on board. If a ground station doesn't see a receiver it will not provide traffic. Consequently the traffic picture provided by a portable receiver to a tablet falls short of a permanently installed receiver. The incremental cost of adding an aircraft mounted UAT receiver is within a few hundred dollars of adding that capability via a portable unit. An aircraft mounted system can provide weather and traffic to multiple displays in addition to a tablet. By contrast, a portable receiver can only provide information to tablet devices. There's also the mess of wires to deal with and solar heating through the glare shield may cause overheating. A permanently mounted solution will not only last longer and be easier to use but will also provide a greater return on investment over the ownership life of the aircraft.
The takeaway: in order to take full advantage of ADS-B-In weather and traffic information, you need a UAT (978 MHz) receiver. With in-cockpit traffic information, pilots can make more accurate and superior tactical traffic decisions compared with the VFR 'see and avoid' method. It's also better than relying on a controller for separation. The pilot is at the center of their traffic picture compared to being just another target on a controller's screen. ADS-B-In traffic makes conflict resolution more collaborative. ADS-B-In weather provides a more complete weather picture than having on-board radar. With ADS-B weather information, pilots can constantly update their weather deviation choices, making smarter and more strategic decisions during flight.