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AOPA comments on National Airspace System (NAS) Architecture Version 2.0AOPA comments on National Airspace System (NAS) Architecture Version 2.0

Statement of the Aircraft Owners and Pilots Association

to the

Federal Aviation Administration
Office of System Architecture and Program Evaluation


Docket Number 96-26823


National Airspace System (NAS) Architecture Version 2.0

February 27, 1997

The Aircraft Owners and Pilots Association (AOPA) represents more than 340,000 general aviation aircraft owners and pilots who flew nearly 25.4 million hours in 1995. Over half of our members own an aircraft either solely or in partnership and account for 96 percent of the civil aircraft fleet in the United States. General aviation clearly has a significant investment in the present system architecture. Any changes in this architecture will have a profound impact on the utility and affordability of general aviation aircraft and avionics. Therefore, significant benefits must be provided to all segments of the user community in order to justify the termination of present systems and encourage users to replace existing avionics with new, advanced avionics systems.

Prior to providing the substance of the Association’s response, we must first commend the Federal Aviation Administration (FAA) for its efforts in compiling, publishing, and communicating the proposed architecture and accompanying data to the user community. Without such a significant effort and opportunity for user input, the process for implementing a desirable change in the National Airspace System (NAS) would be unproductive.

Overall, many decisions seem to be driven more by economics than operational requirements and safety. The proposal also assumes that FAA forecasts for operational growth are correct, when FAA long-range forecasts have historically been overly optimistic. For example, the FAA’s 1989 forecast predicted that IFR operations in 1994 would grow to 41.9 million. However, there were only 38.8 IFR operations in 1989, an 8 percent difference. The average overestimation for FAA five-year forecasts is 6.2 percent, a figure that increases as the forecasts look further ahead. Not only does this result in overly pessimistic budget projections, but it naturally leads to overly aggressive transition plans and technical solutions that will invite negative feedback from general aviation aircraft owners. AOPA will offer alternatives that will be viewed more favorably by the community it represents.

The Association has been involved in a number of government/industry forums over the past few years in which input was provided on specific future architecture concepts. The proposed architecture incorporates some of this input but fails to address the remainder. On the positive side, the FAA has placed major transition steps in a logical, sequential order: navigation and communication, followed by surveillance. Each transition provides a technological capability and an infrastructure on which the next transition can be built. It also has the potential of providing the greatest user benefits in priority and seems to be consistent with the likely evolution of these technologies operationally, economically, and politically. In order for each transition to be successful and expedient, substantial benefits must be provided to the users to encourage acquisition of new equipment. Once these benefits exist and affordable avionics are available, FAA must allocate adequate time for users to budget for new equipment. There must also be adequate time for manufacturers and repair shops to satisfy the demand for avionics and installations.

The most significant problems with the proposed architecture are:

  • The transition periods planned for navigation, communication, and surveillance overlap one another, and each transition period itself is overly aggressive. This strategy is unaffordable for most of the general aviation community. Additionally, it is unlikely the FAA will provide user benefits until well after the scheduled transition periods begin. This will have the effect of compressing the time in which aircraft are expected to be equipped. AOPA believes the proposed schedules are unrealistic.
  • The cost of FAA-certified avionics is escalating and seems to increase with each new technology. The FAA must create a certification environment that fosters low-cost avionics. Without affordable avionics for every segment of the user community, the transition to new systems will generate user resistance and jeopardize funding. Strong consideration should be given to the concept in which the FAA and industry set standards, and manufacturers self-certify their products. The FAA would maintain enforcement powers, which would be exerted on violators.
  • Although publishing calendar dates is helpful in the planning process, each step in a transition is built on previous accomplishments. If, for example, the implementation of the Wide Area Augmentation System (WAAS) is delayed for some reason, the schedule for decommissioning ground-based navigation aids must also be delayed accordingly. Future architecture plans, as well as the Federal Radionavigation Plan, must include interdependencies for each step of the proposed transitions.
  • The government and the user community agree a benefits-driven transition to a new architecture is the most expedient and least controversial means for progress. Without detailed operational concepts for each transition phase, ensuring user benefits will be all but impossible, and the funding necessary to provide such benefits will not be appropriated. The proposed transition to a new communication system is a good example. Users are expected to replace analog radios with more expensive digital radios, yet there is little said about the data link services the FAA will offer to encourage voluntary equipage. Therefore, the architecture plan must include an operational concept, a schedule of benefits to be provided, and a detailed transition plan.
  • Personnel costs account for the greatest portion of the FAA’s budget by far, past, present and future. Version 2.0 provides a good overview of technical system architecture and its cost but fails to show any productivity gains in personnel costs. Ignoring potential gains in this area artificially increases projected funding shortfalls and raises questions about the credibility of the plan overall. No business would invest in modernization without knowing the associated labor benefits. The FAA addresses this area in future versions.


Transition to the Global Positioning System (GPS)

With the availability of precise radio navigation signals down to the Earth’s surface, satellite navigation is already providing segments of the aviation community with operational benefits and has the potential of providing a great deal more. Providing these benefits to all GPS users in a timely manner, at a price they can easily afford, will be the greatest challenge facing the FAA in the transition to GPS.

AOPA believes the proposed transition time lines for decommissioning ground-based navigation aids are overly aggressive. The rate at which the general aviation community will transition to new avionics will depend on numerous factors, including operational benefits provided to the users in both VFR and IFR operations and the availability of affordable avionics for all segments of the user community. For example, the FAA proposes to decommission all VORs in 2008, six years after the WAAS is predicted to provide sole-means capability. This capability, in no way, means that more approaches, direct routings, or low-cost avionics will be available. Even if these conditions existed, expecting more than an average of 10 percent rate of equipage per year seems to be unrealistic. A 10-year transition would seem more appropriate assuming navigation aids were decommissioned in a manner that minimized the impact on the users.

In terms of user benefits, IFR operators gain the greatest operational improvements from the use of stand-alone approaches to airports that have none presently, greater use of direct routes, and less clutter and complexity in cockpits. VFR operators will benefit most from increased situational awareness and the use of direct transition routes through terminal and special-use airspace.

The price sensitivity of various segments of the user community will differ. However, if we examine voluntary equipage with LORAN C over the past 10 years, approximately $2,500 for an IFR-capable receiver seemed to be the price threshold at which most users voluntarily equipped. Early indications are $2,500, in today’s dollars, will likely be the threshold for IFR GPS receivers as well. Additionally, the ongoing cost of maintaining a current database is a significant deterrent to voluntary avionics purchases. The user community already funds the FAA’s collection and storage of this data, so there is no reason this information should not be provided directly to the pilot community. The FAA must develop a cost-effective means of distributing this data to end users at little or no cost. Electronic transfer of this information via satellite broadcast and certainly by online computer networks should be pursued.

The architecture proposal poses the question, “Should the FAA consider subsidizing user equipage?” If the FAA provides users desirable benefits at a cost they are willing to pay, there should be no need for the government to subsidize general aviation equipage. Providing some type of subsidy—a tax credit, for example—could accelerate the transition and ultimately save both the users and the government a great deal of money in the long run, but it appears to be politically unrealistic at the present time.

GPS/WAAS as a Sole-Means Radio Navigation System

AOPA supports the concept of using GPS augmented by WAAS as a sole-means system but believes sole-means service must be well established prior to decommissioning of any ground-based navigation aids. It is not clear at this time what configuration the end-state WAAS must take in order to serve as a sole-means navigation and landing system. The system’s performance and immunity to interference will determine this, but full operational capability as noted in the transition plan must represent this final configuration.

AOPA believes the final WAAS configuration should at least provide dual satellite coverage over the 50 states and that each WAAS satellite should provide GPS pseudo ranging functionality to ensure system performance during GPS satellite failures. New precise timing instruments (i.e., rubidium and temperature compensated crystal oscillator (TCXO) timing technology) provide a relatively low cost means of achieving this. AOPA realizes that WAAS coverage will not be available farther north than about Anchorage, Alaska. The FAA must provide an alternative means of improving GPS system performance in those areas or use alternative systems as a backup such as LORAN C.

Secondary Systems

It is difficult to determine whether two independent navigation systems should be a NAS requirement without having the benefit of significant operational experience with GPS/WAAS. Meeting a technical requirement on paper, like that for sole means, does not necessarily mean operational requirements are adequately fulfilled. Early indications are that local GPS interference, intentional or unintentional, will play a significant role in determining the need for a secondary system. It would be prudent to maintain candidate secondary systems, like LORAN C, until operational experience with GPS/WAAS substantiates the necessary level of service.

Should the need for a secondary system prove necessary, the FAA should invest in upgrading the LORAN C to a primary-means IFR system. Although GLONASS appears to be another option, it is susceptible to the same type of interference as GPS, and provider support (Russian) for this system still remains very questionable. Furthermore, several Asian and Indonesian countries, including Russia, Japan, and China, are in the process of implementing LORAN C as a secondary navigation system. AOPA believes that LORAN C is clearly the better option of the two.

The cost of upgrading the U.S. LORAN system is about equal to the cost of maintaining all the current U.S. navigation systems for one year ($200 million), and upgraded LORAN stations would reduce the annual maintenance cost from $17 million to $10 million. In contrast, today’s VOR/DME system would cost about $100 million per year to sustain and is not cost effective. A skeletal network has been proposed, but an affordable skeletal network will provide very limited coverage and not serve the needs of the general aviation community. It is conceivable that the money saved by resorting to a skeletal VOR/ DME system for high-altitude operators could more than offset the cost of upgrading and maintaining LORAN C.

Operationally, LORAN C as a secondary system would be dissimilar from GPS/WAAS in terms of frequency band and power, making it less susceptible to RF interference (both intentional and unintentional). The result is that interference affecting one of these two systems is extremely unlikely to impact the other. Despite these differences in system architecture, aircraft avionics are designed such that the signal source is transparent to pilots. Additionally, much research and development has already been done and paid for in the marketplace, with limited-capability combination GPS/LORAN avionics already on the market.

There is also a broader issue with regard to the need for a secondary system. It has been proposed that GPS be used not only for navigation, but that its position information be used as a basis for aircraft separation services, as well as a timing source to manage the operation of the proposed digital communication systems. If carried out as proposed, a loss of GPS in a given area, whether local, regional, or global in nature, could mean the failure of all three major system capabilities. Such a failure would prove devastating to air transportation and all that goes with it. It does not seem prudent to use GPS/WAAS as the lynch pin system for navigation, communication, and surveillance simultaneously. Two or three independent systems are probably necessary to ensure uninterrupted services for these critical capabilities. Again, we believe an upgraded LORAN C system is one of the most cost-effective means of providing this requirement. It can provide comparable position accuracy (using differential technology), signal coverage, and timing capability.

AOPA opposes decommissioning LORAN C by 2000 for these reasons and supports extending its operation until at least 2010 based on the current schedule for WAAS full operational capability. At least three years of experience using GPS/WAAS seems appropriate to determine whether or not GPS/WAAS meets user requirements as a sole-means system.

GPS Local Area Augmentation Systems (LAAS)

Augmentation systems serving individual airports for precise landing guidance will be required for Category 2 and 3 GPS approaches. It will also be required for Category 1 approaches at airports that are not adequately served by the WAAS system. The FAA proposes to create standards for LAAS and require individual airport operators to fund the acquisition, installation, and maintenance of these systems. There are some issues that must be addressed before this policy is adopted.

There will be a number of general aviation airports that will not be able to gain the full benefits of the WAAS system due to masking of those signals by local conditions such as high terrain or other obstructions. Regions such as northern Alaska will not be covered by the signal footprint of the WAAS satellites and will likely have to depend on local area systems. Therefore, AOPA believes FAA must continue to fund local area augmentation systems at those airports to fulfill its responsibility of providing access to the National Airspace System.

Legal issues such as liability should be investigated prior to implementing the proposed funding policy. The FAA is currently protected by the Federal Tort Claims Act for incidents and accidents related to the use of existing approach and landing systems. It is not clear if airports supporting local area landing systems will have similar protections or some other means of coping with the associated liability, economically or institutionally.


FAA studies indicate there will be a critical shortage of frequencies to allocate in the high-altitude and large terminal area environments based on forecast traffic growth. Additionally, the FAA will need to replace 40,000 communication radios sometime in the next decade. The proposed solution to this problem is to convert the entire communication system to digital technology and, ultimately, require replacement of all ground and aircraft radios. The proposal calls this new system NEXCOM since the decision on which type of digital technology to be used has not been decided.

AOPA believes the estimated growth sited in the FAA’s forecast is overly optimistic based on growth trends for the last 10 years, and what growth there is will be generated primarily by commercial air carriers. However, the association recognizes that demand for frequencies will continue to increase in the future. A small part of this demand will come from general aviation due to demand for new technological capabilities such as data link, ASOS, and automated unicoms. We further realize that benefits provided by these new capabilities will not be available unless more spectrum capacity is found.

In a spectrum-constrained environment, digital technology is a logical solution since it provides the ability to improve the communication of information between the ground and aircraft and can utilize radio frequency spectrum more efficiently. However, there are many general aviation users who will either not be able to afford the avionics necessary to gain these capabilities or will not require them for the type of operations they conduct. Therefore, it is important to develop a means by which those that want the benefits can access them without imposing burdensome equipment requirements on those who do not.

Further study on alternative approaches to the implementation of new communication capabilities is needed. New technology may permit digital services to be overlaid on existing analog channels. This would utilize the available spectrum more efficiently and negate a requirement to replace all existing analog radios and services.

Another option might be to convert a portion of the communication spectrum to digital technology. This may provide enough data link capacity to provide all the necessary data communication services. It could off-load the analog voice channels, thereby providing enough capacity to accommodate increased demand. For example, utilizing the Aircraft Communication and Addressing Radio System (ACARS) for pre-departure clearances has removed much of the congestion on the clearance delivery frequencies at airports where this system has been implemented and has placed no burden on the users of those airports that were unable to afford ACARS avionics. All these options should be seriously investigated before a decision is made on NEXCOM technology.

The proposal for a complete conversion to digital communications equipment will require all airspace users to replace their existing radios. The cost is estimated to the general aviation community alone of almost $390 million with little or no benefits for many of these users. Alternatives, such as leasing a private network (e.g., ARINC) for data link and maintaining the current analog voice communication system should be studied seriously before forcing fleet-wide retrofit of new radios.

Mandating new communication radios that provide no added benefits has been tried by the FAA before. The FAA attempted to persuade voluntary equipage for well over 20 years to get 720-channel communication radios into the general aviation fleet, and a mandate was still necessary at the end of that period to make it so. This is because there are no perceived benefits of more channels to the average aircraft owner; it just means more air traffic control frequency changes.

The FAA alleges digital radios for general aviation will cost $1,000, an extremely optimistic estimate. Avionics manufacturers have indicated that $1,500 is the lowest price they foresee, and higher costs are likely. If we use FAA survey information and assume that two thirds of the 150,000 general aviation aircraft with electrical systems would require two radios, and the remainder could get by with one, even at $1,500 per radio, that is $375 million. An average installation cost of $200 per aircraft raises that total another $3 million. Additionally, there are another 20,000 non-electrical aircraft, which would have to replace portable radios at a minimum of $600 per unit, bringing the total retrofit cost for general aviation to $390 million. These estimates are optimistic. The true costs will probably be higher, and all of this with marginal benefits.

In order to use data link, a display and processor must be purchased and connected to these radios. The cheapest display/processor unit for aviation today costs $6,000. Adding an aircraft position and surveillance capability will require a certified GPS for position information and additional software and processing capability. Currently, the cost of purchasing and installing a certified GPS is $6,500 minimum. The total cost of acquiring the full benefits from digital radios will be close to $15,000, which would represent more than 50 percent of the value of a used Cessna 172. This is clearly too much.

AOPA surveys indicate that between 30 and 40 percent of general aviation aircraft owners are willing to pay an average of $1,500 for data link information in the cockpit, including processor and display. Less than 10 percent of the respondents were willing to pay more than $5,000 for this type of capability. The top ten applications they expect to receive on these avionics include weather graphics, textual weather reports, airport information, notices to airmen, and traffic information. It is clear from this data that the disparity between current costs and consumer expectations must merge before digital radios are perceived as a benefit.

AOPA believes that if the transition period is long enough, the benefits offered are attractive enough, and the cost of the avionics is truly affordable, the general aviation community will voluntarily equip. However, this transition must begin well after the transition to GPS is under way. General aviation owners simply cannot afford new avionics to transition both navigation and communication simultaneously. Because the FAA plans to acquire radios capable of both analog and digital communication, the transition period should be scheduled to last as long as those radios are supported (probably 20 years or more). Retaining analog unicom and flight service frequencies indefinitely should be considered a requirement until all users of this system equip with new radios. Additionally, the technology of choice must incorporate air-to-air functionality without the need for ground stations.


Eight years ago, the general aviation community was the object of new regulations requiring transponders in aircraft used to operate in certain airspace. Based on FAA survey data, AOPA estimates that approximately 90 percent of general aviation aircraft with electrical systems are equipped with transponders, which accounts for 85 percent of the fleet. Achieving this level of equipage has taken years and cost the users million of dollars. Therefore, it is imperative that any new surveillance technology provide a true user benefit at a low cost.

Automatic Dependent Surveillance-Broadcast (ADS-B) holds the promise of being the surveillance technology of the future. It uses data link technology to transmit an aircraft’s position coordinates to anyone who requires it. GPS is the preferred source of position information for this purpose. Assuming the aviation community transitions to GPS and that data link becomes part of the communication system, there is no reason that the same systems could not be used for ADS-B information. This would provide a means for getting the technology into aircraft without forcing the replacement of transponders, and would most likely be the most affordable alternative for the users.

The FAA is moving toward Mode S as the data link of choice for ADS-B. There are a number of problems that make this unrealistic as a long-term solution. It would require a special data link radio that would be limited to providing only this capability. Additionally, tests have shown that the frequency characteristics of this system cause some significant technical problems when installing it on small airframes. Technical remedies for these problems have yet to be developed and will certainly increase the avionics costs to the point that they will be unaffordable by most of the general aviation community.

Conversely, VHF does not share these same characteristics, but availability of spectrum is a greater obstacle. Using the portion of the VHF spectrum currently assigned to VORs is the obvious solution. This can be done once the transition to GPS is completed and the VORs are decommissioned. This is a logical transition path since the position information used for ADS-B relies on GPS. It also conforms to the general aviation community’s desire to deal with one technology transition at a time. Any transition to ADS-B for surveillance must include the provision of Traffic Information Service functionality in which surveillance data collected and processed in air traffic control facilities is provided to aircraft equipped to use it. This provides desirable traffic information to those that want it and can afford it without forcing all users to buy new equipment in order to be monitored.

The design of the ADS-B system and avionics must be inexpensive and provide benefits for users that cannot afford or may not need expensive IFR certified GPS and data link avionics. Most of this community now fly aircraft that are required to be equipped with transponders and emergency locator transmitters (ELTs). ADS-B has the potential of providing the functionality of both an ELT and a transponder for lower acquisition and maintenance costs. This would be considered a benefit to this segment of the community. They would gain the advantage of being seen by other aircraft equipped with traffic information displays and, potentially, being rescued sooner after a survivable crash.

These avionics should not be expected to survive a crash but could be monitored continuously via geosynchronous satellites, such as those to be used for the WAAS. Traffic information could be down-linked by these satellites to a monitoring station that would record this data. If an aircraft’s ADS-B unit was unable to transmit a distress signal before it was destroyed, the recorded data could be used to locate the downed aircraft’s last known position. Because satellites would monitor the aircraft down to the ground, this position would be at, or very close to, the crash site. This traffic monitoring function could also be used as a backup to the ATC ground system.

The FAA would ultimately save money since a ground station used to receive ADS-B information is much less expensive than secondary radar systems. Those savings would also combine with reduced search and rescue costs. A portion of those savings could then be used to pay for satellite surveillance of ADS-B equipped aircraft for search and rescue/ELT functionality purposes and as a backup to a secondary surveillance radar system failure. There would be a latency-of-position information to consider in the backup scenario, but it would be far superior to procedural separation. Primary radar should be retained indefinitely as an independent back-up to ensure safety during failures of the ADS-B system and avionics.

Weather. Behind pilot error, weather continues to be the causal factor in the greatest number of aviation accidents. Collection and dissemination of weather information remains a safety critical function, is a regulatory requirement, and should remain a government function. For this reason, AOPA agrees that an online computer system must be supported and that a human expert must be available to interpret weather data when needed. As the user community continues its move toward computer services, lesser demand will be placed on the human element of the dissemination system, and further consolidation of this service may take place. However, it is extremely important that this evolution is done at a pace dictated by demand and not arbitrary government policy.

At the same time, graphical weather products and briefing services must improve. Graphics presently provided via the Direct Users Access Terminal System (DUATS) are an improvement over no graphics at all but are wholly inadequate in today’s environment of advanced technology and are relics from teletype days gone by.

Better weather information is needed in general aviation cockpits. Pilots currently rely on only voice services to receive all weather reports. Data link technology makes it possible to receive and display textual and graphical weather information in the cockpit. Other information that should be provided includes special-use airspace status, notices to airmen, automatic terminal information system (ATIS) broadcasts, and ATC clearances. These products and more will have to be disseminated by the FAA if users are to be enticed to purchase new communication radios. The necessary communication networks will have to be in place to make these products available anywhere in the system. The use of broadcast services will minimize the cost of the avionics and make these important safety services available to the greatest number of users. Satellite systems would be best suited to provide broadcast services, and VHF ground networks would be best suited for request-reply services. Mode S is undesirable for either application due to its limited capability in terms of capacity and signal coverage and its cost and complexity.

Improved weather information is also a must if the products are to be of value at low altitude for general aviation. This can only be done by adding sensors and improving data processing. Pilots operating under visual flight rules rely heavily on ceiling and visibility reports and forecasts. Additional ASOS sites and dissemination of non-federal AWOS and ASOS reports are the primary means of achieving this. Pilots operating under instrument flight rules rely not only on ceiling and visibility forecast, but also thunderstorm, icing, and turbulence reports and forecasts. Data link will allow them to use information provided by additional weather radar sites, more precise icing forecasts, and satellite imagery. The FAA should provide these products if it expects to make any significant strides towards its goal of zero accidents.

Ground Automation

Many of the benefits that are to be provided by new technology rely on the implementation of enhanced air traffic control (ATC) tools and procedures. For instance, direct routing transiting terminal areas may not be possible unless controller workload is decreased by providing them with new tools to handle separation services more efficiently, such as a conflict probe. Until some of these tools are implemented, many of the potential benefits provided by new aircraft avionics will not be realized.

Implementation of automation usually makes it possible to improve human efficiency rather than replace it. This will be true of many of the air traffic controller tools. Because humans will need to routinely interact with automation, human factors will play a major role in system productivity. Work should be accelerated including field trials, so that the users and the FAA can more rapidly expect benefits from new technology.

Avionics Certification and Installation Costs

User benefits come in two general forms: (1) significantly greater capability (e.g., GPS in lieu of LORAN, VOR, ILS, ADF, DME, RNAV, etc.) at comparable cost, or (2) comparable capabilities at a significantly reduced cost. Any move to new technologies should provide a combination of both these benefits in order to expedite voluntary equipage. For example, it must be assumed that users have been forced to replace old equipment with new models of the same technology up until a GPS receiver provides all the capability afforded by today’s avionics suite. The infrastructure used by existing avionics must be maintained long enough to provide a reasonable rate of return of at least 10 to 20 years.

Benefits and affordable avionics must exist several years before current ground-based systems begin to be decommissioned. It could then be anticipated that an average of 10 to 15 percent of the general aviation fleet would equip on an annual basis. This translates into a seven- to 10-year period to equip the entire fleet.

The FAA must find new, less expensive ways to control safety. The certification process increases the cost of equipment significantly. This has forced the user community to resort to uncertified equipment such as “handheld” GPS navigators and moving maps. Certification standards are often set artificially high due to a misperception that the systems we use today meet that standard, when they likely do not. Additionally, the approval process for installations in aircraft is very cumbersome, time-consuming, and expensive.

There are a number of efforts that have the potential to reduce certification costs. One such effort is being supported by the manufacturers involved in the National Aeronautics and Space Administration’s (NASA’s) Advanced General Aviation Transport Experiment (AGATE) program. They are striving for agreement on a standardized avionics data buses that would allow for interchange of avionics in airframes. Compliance with this standard would provide a short-cut to FAA certification. But the whole certification program needs to be reviewed and questioned.

Is there a real need to certify every piece of equipment that goes into a general aviation aircraft? Historically, non-certified avionics have been used in general aviation aircraft to navigate and communicate under IFR (VORs and VHF communication radios without formal technical standard order approval) with no compromise in safety. If not for a recent policy change by the FAA, this could be done today with certain avionics. It is clear that something must be done to reduce the cost of certification, or it will be unaffordable for the general aviation community to keep pace with technology. As previously mentioned, standards should be established and manufacturers should be permitted to self-certify their products. FAA enforcement and potential litigation would be strong deterrents for would-be violators.

In summary, AOPA believes the proposed architecture provides the correct order in which to transition to specific technologies, but that the transition time frames are overly aggressive and unaffordable. A detailed operational concept is needed to quantify the benefits, assess the impacts, and justify the required change in avionics. Finally, more work is needed to define technology types that are affordable and beneficial to the user community before a decision is made to transition to new technology. The association looks forward to your response and its continued involvement in managing the transition to the future aviation system.

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