ADS–R принимает данные на частоте 978 MHz UAT и ретранслирует ее на частоте 1090 MHz ES.
Тоже самое и наоборот, таким образом информацией снабжаются как самолеты с ADS-B так и с UAT в обе стороны.
Under a dual-link strategy, the FAA will use ADS–R to allow ADS–B Inequipped aircraft using one type of broadcast link to receive messages about aircraft transmitting on the other broadcast link.
Various commenters, including the Air Transport Association of America, Inc. (ATA), Airservices Australia, the Australia Civil Aviation Safety Authority, the Aircraft Owners and Pilots Association (AOPA), Boeing, British Airways, and the International Air Transport Association (IATA), expressed concern about a dual-link system.
Some of these commenters asserted that the need for ADS–R introduces additional system-wide latency into the ADS–B system and poses a single point of failure for the degradation or loss of surveillance data. In their view, this could limit potential separation and efficiency improvements and affect the air-to-air surveillance element of future ADS–B In applications.
In addition, some commenters expressed concern about the additional risk of faults or failures that could result from translating, merging, and rebroadcasting data from the 1090 and 978 MHz frequencies. Some commenters, including Boeing, contended that ADS–R may not have sufficient growth capability to support future ADS–B In air-to-air applications. Such applications include merging and spacing, self separation, or using ADS– data to supplement or replace TCAS because of potential of latency or loop delays. Rockwell-Collins stated that ADS–R should be able to support many ADS–B In air-to-air applications, including closely spaced parallel approaches and enhanced visual approach.
It recommended developing ADS–R to support more demanding aircraft surveillance applications (ASA). Several commenters, including AOPA, asserted that the dual-link system presents a safety hazard because aircraft equipped with different links cannot ‘‘see’’ each other on ADS–B In displays in areas without ADS–R coverage. The commenters suggested providing ADS–R at all public airports where a mix of both systems will be encountered.
The FAA is deploying ADS–R in all areas where ADS–B ATC surveillance exists.
ADS–R collects traffic information broadcast on the 978 MHz UAT broadcast link and rebroadcasts the information to 1090 MHz ES users. Similarly, ADS–R collects traffic information provided on the 1090 MHz ES broadcast link and rebroadcasts the information to UAT users. ADS–R permits aircraft equipped with either 1090 MHz ES or UAT to take advantage of ADS–B In applications.
The FAA disagrees with the comments suggesting that ADS–R introduces safety issues because of the added latencies attributed to ADS–R processing. ATC automation systems do not require or use ADS–R to provide surveillance. The added latency in the rebroadcast of the original ADS–B message are measurably small and do not degrade the reported NACP, NACV, and NIC values.
The ARC agreed in its report that the latency in ADS–R processing does not degrade the reporting of the position quality parameters.27 Latency attributed to ADS–R does not compromise the safety of the initial ADS–B In applications. The intended functions of ADS–B, as identified in the NPRM, are not compromised by the latency introduced with rebroadcasting the messages. However, future ADS–B In applications necessarily may be limited becauseof the latency associated with ADS–R.28 The FAA has a strong interest in providing the option for operators to equip with UAT, so they may benefit from FIS–B service.
In making the decision to use a dual-link strategy, the FAA acknowledged and weighed the fact that potential benefits of future applications may not be fully realized based on this decision. In situations where an airport is not within the planned ADS–B coverage area, the airport will not have ADS–R coverage. Consequently, an aircraft with ADS–B In will not have the benefit of ADS–R, and ADS–B In will not provide awareness of aircraft that are broadcasting on a different broadcast link. If an aircraft leaves the ADS–B coverage area, there will be an indication to the pilot that the aircraft is no longer within range of ADS–R service.
In this case, the pilot needs to maintain separation in the same manner done today, which is relying on visual scanning and directions from ATC. The FAA will ensure that the dual-link strategy does not impact safety as future applications are developed.