FAA Response:The text does not imply the need for dual independent navigation computers. The text instead emphasizes the need for independence of the navigation systems and their components to ensure that there will be no potential single point of failure or event that could cause the loss of the ability to navigate along the intended route or proceed safely to a suitable diversion airport. The interpretation of this requirement as applied to an aircraft approved for multi-sensor navigation and equipped with a single FMS is that the aircraft must maintain an ability to navigate or proceed safely in the event that any one component of the navigation system fails, including the FMS. Retaining an FMS-independent VOR capability would satisfy the requirement, even as the NAS is transitioned to the MON. This interpretation corresponds to the advisory wording in AC 20-130A.
Comment #15:The Maryland Aviation Administration (MAA) expressed concern about current GPS equipage rates.
FAA Response:Though approximately 19 percent of all general aviation aircraft are equipped with aviation-qualified GPS, most aircraft that actually file IFR flight plans are typically equipped with GPS. Specifically, more than 72% of aircraft that filed at least two IFR flight plans in 2011 filed with an equipment code indicating they had IFR GPS receivers on board. Of aircraft that filed more than 100 IFR flight plans in a year the rate was above 97%. While it may be the case that a significant number of aircraft flying VFR are not equipped with GPS, the purpose of the VOR system is to provide navigation for aircraft flying IFR, not VFR. VFR traffic is permitted to use hand-held and non-IFR certified GPS equipment for situational awareness as an aid to navigation and often use pilotage and dead reckoning navigation. While the VORs retained in the MON will support VFR aircraft operations, their purpose is clearly to support those aircraft operating under IFR.
Comment #16:Two commenters (the Nebraska DoA and Thales) were concerned over the impact that a reduction in VORs would have on training and training requirements.
FAA Response:The current training standards for the FAA emphasize VORs as the primary navigation source. The transition to NextGen will require that the FAA shift emphasis from VOR navigation to satellite-based navigation by changing training syllabi and the PTS. However, some emphasis will need to remain on VOR and ILS to ensure that pilots can navigate using these systems in the event of a GPS outage. These considerations will be included in the FAA's plan for discontinuance of VORs. Additionally, transfer of FAA-owned VORs not selected to be in the MON to operation under non-Federal ownership for training may be considered on a case-by-case basis.
Comment #17:The Nebraska DoA and Thales were also concerned with airport infrastructure requirements resulting from development of RNAV or RNP approaches.
FAA Response:FAA airport infrastructure requirements resulting from instrument approaches are published in FAA Advisory Circular 150/5300-13. Because airport infrastructure upgrades may be required for the attainment of lowest instrument approach minima, collaboration with local and state officials will be accomplished during the approach development process. For example, development of an LPV approach could not be accomplished if the required runway length were not available. However, if a decision was made in collaboration with local and state officials, to extend the runway, then an LPV could be reconsidered.
Comment #18:United Air Lines and GE Aviation expressed concern on the use of GPS approach capability by air carriers at alternate airports.
FAA Response:Current FAA policy allows operators of aircraft equipped with WAAS to plan for RNAV (GPS) approaches to the LNAV line of minima at their alternate. Furthermore, the FAA is currently investigating what requirements will be necessary to allow un-augmented GPS (TSO-C129/-C129a, TSO-C196/-C196a) equipped aircraft to plan for RNAV (GPS) or RNAV (RNP) approaches at alternate airports.
Comment #19:Several commenters expressed concern that the navigation transition strategy as outlined in the FRN is indirectly requiring certain types of equipage, specifically GPS or WAAS equipage.
FAA Response:The FAA is committed to the use of performance-based operations in the NAS. They remain the optimal way to both enable technological advances while maintaining safety, efficiency and consistency. Therefore, it is not the intention of the FAA to limit operational approvals to specific technologies or to force retrofit navigation solutions on current operators with legacy equipment. VOR navigation will continue to be a viable option for airspace users for the near future. Once the FAA completes implementation of the VOR MON, VOR navigation will still serve the NAS, albeit in a less robust fashion than today. Early publication of transition considerations and planning will allow users to consider long-term equipage strategies for their aircraft. Operators are encouraged to continue to seek approvals for the use of navigation equipment that was emphasized in the FRN, e.g. DME/DME/IRU, GPS, and WAAS. The FAA will continue to work with industry to advance new technologies not yet matured, e.g., GBAS and APNT. Additionally, the FAA will continue to work with our international partners on global strategies for multi-constellation/multi-frequency GNSS solutions.
Comment #20:AOPA and the National Business Aviation Association (NBAA) both expressed support for direct routing and avoiding excessive implementation of additional T and Q routes.
FAA Response:In the NextGen environment, T and Q routes increase capacity and efficiency while maintaining safety by minimizing impact to air traffic control. T and Q routes allow controllers to safely manage air traffic during peak periods and to ensure predictable transitions between busy traffic areas. T and Q routes overlaid on existing airways defined by VORs could mitigate potential impacts to the discontinuance of VOR navigation services.
Comment #21:Comments from military and general aviation expressed interest in participating in VOR discontinuation planning.
FAA Response:As stated in the FRN, “The FAA will convene a working group that will develop a candidate list of VORs for discontinuance using relevant operational, safety, cost and economic criteria. As part of the process, this working group will engage aviation industry stakeholders and other members of the public for input.” Detailed planning for the implementation of the MON is still under development. As the program planning process is further developed, the FAA will solicit input from government and industry stakeholders before the VORs selected for the MON are finalized.
Comment #22:Several commenters (MAA, Boeing Commercial Airplanes, United Air Lines, AOPA, Thales and DoD) indicated that an overall plan is necessary and requested more detail on the MON. MAA commented that without a national plan for discontinuation, the removal of specific VORs from service might be premature. They believed that several VORs in Maryland are currently planned for discontinuance and they suggested that the discontinuation of specific facilities should be considered on both a regional and national level using analysis to identify costs and benefits in a more holistic manner to make the consideration of facilities objective and consistent.
FAA Response:The FAA has not developed a final list of VORs that will be included in the MON. The FAA is developing objective criteria, which will be applied consistently both nationally and regionally to help identify those VOR facilities that will remain operational. A specific overall national CONOPS and discontinuance plan are being developed to support this effort. The draft CONOPS and draft discontinuance plan will be presented to stakeholders, and the FAA willengage stakeholders in the discontinuance process.
Comment #23:Military and airline industry commenters expressed concern with the FAA plan to establish the VOR MON by January 1, 2020.
FAA Response:This date coincides with the January 1, 2020 mandate for ADS-B equipage. Once aircraft are equipped with ADS-B, it is assumed that they will be equipped with GPS as well, since currently GPS is the only known position source that can satisfy the NIC/NAC/SIL requirements of ADS-B. At that time, the VOR MON will serve as the required GPS backup for non DME-DME equipped aircraft in the event of a GPS outage. By January 1, 2020, the VOR MON will provide sufficient VOR coverage to enable aircraft to fly VOR-to-VOR either through the GPS outage or to a safe landing.
Comment #24:A number of operators, service providers and equipment manufacturers were concerned about the level of reliance on GPS expressed in the FRN in light of possible interference with the GPS service. Interference on a regular basis from government testing and training was specifically identified, as was possible widespread interference from licensed operators as well as unintentional interference from a variety of human and natural sources. There remains a concern among users that GPS is susceptible to interference and VORs should remain as a cost effective reliable means of navigation.
FAA Response:U.S. National policy recognizes the vulnerability of GPS signals, from both human and natural sources, and requires operations reliant on GPS position, navigation, and timing (PNT) for safety, security, or significant economic benefit to have sufficient backups in place. The FAA has operated and will continue to operate GPS-independent systems to fulfill this requirement, such as ILS, DME, and VOR. As the NAS transitions to NextGen, there is also a requirement to move from conventional facility based navigation to point-to-point navigation using PBN, a role that the airways supported by VORs cannot support. The FAA will continue to operate a subset of the current VOR facilities in a MON to support those aircraft not equipped with GPS-independent RNAV capability, while developing an RNAV-capable APNT system to fulfill this role in the future. DoD Interference with GPS: The FAA recognizes the need for DoD elements as part of their mission to operate and conduct training in a GPS-denied environment. Both the FAA and DoD are committed to working together to ensure that the DoD mission will not impact the FAA's mission to operate a safe and efficient NAS. DoD GPS interference testing is fully coordinated with the FAA and prior to testing, the FAA issues a Notice to Airmen (NOTAM) that describes the potential extent of interference and the timeframe in which it might occur. During testing the FAA maintains direct communications with DoD at all times and can have tests suspended in the event of any impact to NAS operations. Today, aircraft with non-GPS RNAV avionics are not impacted by this interference, and in the future, all APNT-equipped aircraft will similarly be unaffected.
Comment #25:Comments were received relative to several specific VORs with reasons for their specific retention. In the case of the Wichita, KS VOR (ICT), it was stated that the facility is needed for testing and airworthiness demonstration of new manufactured aircraft by a number of companies in the area.
FAA Response:While a VOR signal is necessary for this activity, it is not necessary that the service be provided by a FAA owned VOR, whose purpose under the MON will be to ensure safe operations in the event of a GPS outage. A non-Federal VOR, owned by an airport authority, state instrumentality or private entity could also perform this function. In cases where individuals/organizations have an interest in maintaining a specific VOR service, the VOR could be transferred to and operated under agreement with the FAA as a non-federal facility.
Comment #26:Thales expressed a concern over how the VOR MON will support non-GPS aircraft and GPS aircraft during GPS interference if a key MON VOR is down for maintenance.
FAA Response:In determining the VORs that will make up the MON, consideration will be given to the availability and continuity of navigation service expected from each facility. The VOR MON's purpose, a non-PBN backup in the event of a GPS outage, will be considered in making this determination. An element of this consideration will be the availability of non-GPS dependent surveillance services that would allow air traffic to provide services in the event of both a GPS and individual VOR service outage. Additionally, the equipage rate of IFR traffic with IFR GPS is significant and expected to be near 100% as we approach the year 2020 ADS-B mandate. While possible to fly IFR using the VOR MON, the increased distance of the VOR-only route as compared to using RNAV navigation will likely be highly undesirable. This will further drive GPS equipage.
Comment #27:The DoD stated concern on the cost of transition versus benefits for their fleet of aircraft.
FAA Response:The NAS' transition to NextGen is a national priority, in which the FAA plays an important role in concert with other Federal agencies and the aviation community. The transition to PBN as enabling capability for NextGen is a key part of the NGIP. Additionally, the considerations of the military in transitioning a 14,600 aircraft fleet and operating practices to RNAV/RNP stated in comments to the public docket appear to include the notion that TACAN services from VORTAC facilities will be terminated when VOR service is discontinued. This is not the case. The military also desires the FAA to retain VOR and TACAN service for specific enroute and terminal locations and procedures as the military aircraft fleet equipage and operating procedures evolve.
The FAA notes that there is historic precedent for the transition to a single national system—specifically the establishment of VORs and associated airways, DME, and ILS in the 1950s. At that time the military did not want to equip with VOR or ILS in tactical aircraft due to weight and space constraints, stating that Non-Directional Beacons (NDB) and four course ranges for enroute navigation and ground controlled approach (GCA) for landing was sufficient pending implementation of TACAN. The military also wanted to evolve to use TACAN because of weight/size and operational advantages over VOR and to include their implementation of DME, rather than the civil DME standard. The civil community, particularly airlines, wanted VOR for improved accuracy and usability over four course ranges and NDBs with ILS for approaches. In the end the NDBs and four course ranges were retained until military aircraft and operating practices transitioned to TACAN, the military DME standard was adopted for all DMEs and ILS was standardized for approaches, though the military continued GCA approaches, particularly for tactical aircraft.
The transition to RNAV/RNP may be undertaken economically for military aviation by retaining TACAN as a system, discontinuing only specific facilities on an individual basis; incorporating military use considerations for identifying VOR service for discontinuation in enroute and terminal environments; designating special use airspace and other military usage features with RNAV references as well as TACAN or VOR rho/theta anddistance references; and retaining ILS at current sites with installation of new ILSs by military where needed in lieu of LP and LPV.
Issued in Washington, DC, on August 14, 2012.
Acting Manager, Navigation Programs.