The Differences Between ADS-B Out and ADS-B In

FAA NextGen ADS-B
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FAA

Automatic Dependent Surveillance-Broadcast (ADS-B) equipment allows air traffic controllers and participating aircraft to receive extremely accurate information about aircrafts' locations and flight paths, which, in turn, allows for safer operations, more direct flight routes, and cost savings for operators.

ADS-B is an important part of the Federal Aviation Administration's (FAA's) Next Generation Air Transportation System (NextGen). ADS-B uses Global Positioning System (GPS) satellites and is a great improvement over the radar-based air traffic control system that has been in place since 1960.

Two types of ADS-B equipment can be installed on an airplane: ADS-B Out and ADS-B In. Both are valuable, but only ADS-B Out is mandated by the FAA to be installed by January 1, 2020, on all aircraft that currently require a transponder. 

ADS-B Out

An aircraft equipped with ADS-B Out equipment will continuously transmit aircraft data such as airspeed, altitude, and location to ADS-B ground stations. Those data are then transmitted to air traffic control stations. To be compliant with the FAA mandate, either a 1090 MHz extended squitter (ES) with a Mode S transponder or a dedicated 978 MHz universal access transceiver (UAT) must be installed. The aircraft also needs a WAAS-enabled Global Positioning System (GPS) receiver.

The 1090 MHz Mode S transponder is required for aircraft that fly at 18,000 feet and higher and is the standard throughout much of the world. The 978 MHz UAT is primarily marketed to general aviation (GA) pilots as it can be used only below 18,000 feet and in the United States.

The cost of purchasing and installing the ADS-B Out equipment starts as low as about $4,000 and runs as high as $200,000, depending on the equipment selected and the type of aircraft involved.

The Aircraft Owners and Pilots Association (AOPA) says ADS-B Out equipment transmits data just about every second, compared with every three to 15 seconds for radar.

That greater timeliness improves the accuracy of information for those conducting search and rescue operations for missing planes.

ADS-B Out will also permit more optimal spacing of planes and will enable better flight paths for planes in areas without radar, including over the Gulf of Mexico and in parts of Colorado and Alaska.

ADS-B In

ADS-B In is the receiver part of the system. It allows properly equipped aircraft to receive and interpret other aircraft's ADS-B Out data on a computer screen or an electronic flight bag (EFB) in the cockpit. (An EFB is a portable electronic device, like a tablet computer, that gets its name from its ability to replace the 38 pounds of paper charts and manuals that pilots had to tote onto every flight.)

The ADS-B In function requires an approved ADS-B Out system and an ADS-B-compatible display interface if pilots want to be able to utilize ADS-B's graphic weather and traffic information.

A study by researchers at airspace systems engineering firm Regulus Group that looked at accident rates for GA planes and air taxis from 2013 through 2017 found that the aircraft were 48-53 percent less likely to have an accident and 88-89 percent less likely to have a fatal accident if they were equipped with ADS-B In. The ranges resulted from two different methods of looking at the data: by fleet and by flight hours.

Traffic and Weather

Traffic Information Service-Broadcast (TIS-B) provides information on the locations of other aircraft, along with their altitudes, direction, and speed vectors. TIS-B works with either the 1090 MHz ES or 978 MHz UAT ADS-B options.

Flight Information Services-Broadcast (FIS-B) provides weather data as well as other important information, such as temporary flight restrictions and Notices to Airmen (NOTAMs). It can be received only through certain compatible UATs; it's not available with the ES option.

The FAA does not charge for either of those services in order to promote the use of ADS-B In.