March 3 was not an auspicious day for officials in the FAA’s ADS-B Program Office. That was the final day for submission of comments from the user community on the agency’s notice of proposed rulemaking (NPRM), which described how ADS-B would be introduced into the National Airspace System (NAS), and the means and timing of required user compliance. But the overall negative tone of the comments must have disappointed agency planners, who are now faced with rethinking many of the details of their proposals.

The FAA certainly expected some negative comments about ADS-B–it receives some for virtually every NPRM–but agency officials anticipated general user community approval of its ADS-B proposals. According to one FAA insider, the agency certainly did not expect the critical responses from many of the organizations that the FAA expected to be supportive. The two most influential–the Air Transport Association (ATA) and the Aircraft Owners and Pilots Association (AOPA)–made their dissatisfaction abundantly clear. The former commented, “The NPRM is materially deficient,” while the latter said, “The proposed rule is not acceptable in its current form.”

Limited Functionality
ADS-B is commonly understood by most pilots as being a system where all aircraft would transmit omnidirectionally their idents, positions, flight paths, altitudes and intent (climbing, descending or remaining level) once per second, and where each would have a cockpit display of traffic information (CDTI) showing the same data from all other traffic in the vicinity plus, in some installations, weather and other flight data. In this way, all pilots obtain continuous situational awareness. Almost without exception, user responses to the NPRM unhesitatingly lauded FAA’s move to introduce ADS-B to the NAS.

Unfortunately, the NPRM introduced only the first, transmitting, part of the system–called ADS-B out–in its 2020 mandate. Adding the second, receiving, part–called ADS-B in–to produce a “full” ADS-B installation was only a recommended option, with no firm date for its mandate, other than being beyond 2020. It was this “half full/half empty”-glass approach, coupled with requirements that many feel are unduly onerous, that has created the widespread dissension.

As for its applicability, the proposed rule would require all aircraft to carry ADS-B out equipment after Jan. 1, 2020, when operating in Class A, B and C airspace over the 48 contiguous states, and Class E airspace above 10,000 feet msl. Carriage would also be mandatory up to 10,000 feet within 30 nm of FAA-specified busy airports.

ADS-B out would also be required in Class E airspace out to 12 nm from the coastline over the Gulf of Mexico, at or above 3,000 feet. Above FL240, the equipment must use the international 1090 MHz extended squitter (ES) datalink, while below FL240, operators may use 1090ES or the general aviation 978 MHz universal access transceiver (UAT) link. ADS-B ground stations will translate signals received in either format and uplink them in the other, to ensure commonality.

User Comments
The FAA received more than 300 comments on the NPRM by the March 3 cutoff date. These ranged from simple “I don’t want it” responses to detailed analyses of the proposal from industry heavyweights, with Boeing’s tour de force running
to 52 carefully reasoned and technically supported comments on specific issues. Shorter but equally well informed technical critiques came from ATA, the DOD, IATA, Airbus, Eurocontrol, NBAA, Lockheed Martin and several private individuals.

Space obviously prevents any attempt to review all that material here, and we can therefore only touch on a few of the more contentious issues and the general responses to them. At press time, the FAA had not publicly addressed any of them, and there is no official deadline by which the agency has to respond.

• ADS-B out is required for all aircraft. This drew wide comment, based on the fact that purchasers will realize no tangible benefits, since these will go primarily to ATC and ADS-B in operators.

• Current transponders will still be mandated as backups in case of ADS-B outages, and an upper fuselage antenna must be added for signal reception “diversity.” AOPA and others strongly opposed both requirements, since ADS-B had been widely seen as a next-generation replacement for legacy transponders.

• Since GPS accuracy is inadequate for ADS-B, receivers must be augmented by WAAS. Many respondents opposed this requirement, pointing out that WAAS-level accuracy was required only for the most advanced all-weather surface movement applications. Others suggested that adding WAAS to airline and DOD aircraft would be prohibitively expensive, and that tightly coupled GPS/IRS would be equally accurate, and will be more likely found in the growing numbers of RNP-capable aircraft. Future satnav configurations, such as Europe’s Galileo and the possible decommissioning of WAAS, were also mentioned as adding uncertainties here.

• Jan. 1, 2020, is the mandatory ADS-B out equipage date. To some in general aviation this was too early, but for United Airlines, it is far too late. UA and other airlines would like to see the end date brought forward to 2015, with mandatory installation required in all aircraft built beginning in 2011.

• ADS-B is a key element in the FAA’s future NextGen program. Several responders acknowledged this, but asserted that NextGen is, as Boeing diplomatically put it, “generally immature at this point.” Some European responders noted that several NPRM requirements conflicted with related technical agreements already reached with the FAA, while others pointed out areas where the NPRM conflicts with current ADS-B operations in Australia, Canada and elsewhere.

• Avionics standards. The NPRM calls for avionics equipment to be compliant with RTCA DO-260A software standards, which are still being developed. NBAA pointed out that more than 5,000 aircraft are currently flying ADS-B-capable installations that meet the earlier, non-TSO’d DO-260 standard. The NPRM does not consider “grandfathering” these while the later DO-260A is finalized. Complicating this, there are different versions (1, 2 and 3), with the FAA and Eurocontrol still negotiating which will be the future standard.

• The NPRM referred to, but did not commit to or support, various financial or operational incentives for early ADS-B out equipage. AOPA and NBAA, among others, strongly advocated such programs. (One FAA insider described NBAA’s response, which contained 12 specific recommendations, as “refreshingly sensible.”) Without installation incentives, many responders felt the plan would be off to a slow start.

• Costs of compliance. There was virtual unanimity that the NPRM seriously underestimated the user costs of ADS-B out. In one example quoted by Boeing, the FAA’s estimated costs for jet installations ranged from a low of $3,862 to a high of $135,736. Boeing’s equivalent estimates were $16,000 to $510,000.

What’s Next?
Is it now therefore back to the drawing board for the FAA? Some of the commenters hope so. In fact, in its comments, the ATA suggested that the FAA should publish a “supplemental” NPRM that would, essentially, replace the current version.

Unquestionably, the FAA now has a major challenge on its hands. Equally certainly, operators who may be considering early ADS-B out installations are strongly advised to read the submitted NPRM responses before committing to avionics work on their aircraft. These responses describe the key issues in easy-to-understand language, which could greatly help in interpreting the to-ing and fro-ing between FAA and industry, and the possible changes that could follow in the months ahead.