Through our modernization efforts, the FAA is creating new interconnected systems that fundamentally change and improve communications, navigation, and surveillance in the National Airspace System (NAS):
Communications: In a modernized NAS, aircraft must be able to receive dynamic, complex instructions from ground systems that can identify where they need to be and at what time. Data Communications helps pilots and air traffic controllers to communicate more quickly, more easily, and with less risk of miscommunication than radio messages over busy frequencies.
Navigation: The FAA has switched to a primarily satellite-enabled navigation system that is more precise than traditional ground-based navigation aids. Satellites enable the FAA to create optimal flight paths anywhere in the NAS for departure, cruising altitude, arrival, and landing operations. These precise, efficient procedures can reduce flying time, fuel use, and aircraft exhaust emissions while getting passengers to their destinations at more predictable times.
Surveillance: The ongoing implementation of NextGen provides air traffic controllers with the exact location of aircraft and a clear vision of surrounding conditions, including weather patterns and aircraft.
With changes in these three core areas and others, NextGen significantly improves overall capacity, performance, efficiency, and predictability throughout the NAS.
Key Enabling Programs
Data Communications (Data Comm)
Historically, pilots and controllers communicated primarily by voice over the radio. Voice offers immediate communications with aircraft, yet also involve time-consuming processes to read and confirm instructions, especially during multiple aircraft reroutes. Other challenges from use of voice communications may arise from a pilot potentially failing to hear or misunderstanding a message, or perhaps acting on directions meant for another aircraft. As a supplement to voice communications, the FAA began developing Controller Pilot Data Link Communications (CPDLC) in the 1990s, initially to support flights over oceans. Data Comm applications like CPDLC provide air traffic controllers and pilots with the capability to quickly and accurately send, review, and accept text-like digital messages. Air carrier flight operations centers receive the same information at the same time as the flight deck, providing decision makers with shared awareness for faster reaction and agreement to flight changes.
The FAA is delivering Data Comm to transform NAS operations. This effort Involves working closely with aircraft operators, airframe and avionics manufacturers, and commercial communications service providers. We anticipate Data Comm will save operators more than $10 billion during the program's 30-year life cycle; the FAA will save about $1 billion in future operating costs.
Data Comm Tower Service
Data Comm Tower Service provides CPDLC digital departure clearances. The FAA completed its original commitment for Data Comm tower service to 55 airports in December 2016, $72 million under budget and almost 30 months ahead of schedule. We then deployed Data Comm Tower Service to an additional seven airports, which were completed in August 2018, almost 13 months ahead of schedule.
More than 6,000 aircraft flown by more than 75 domestic and international air carriers, as well as several dozen business jet operators, can supplement voice communication with digitally delivered departure clearances. These clearances are the instructions pilots receive before takeoff to get to their destinations. Controllers send more than 8,500 Data Comm departure clearances every day.
When weather or other factors delay departures, revised clearances sent through Data Comm improve accuracy and controller productivity. Controllers can deliver multiple CPDLC messages in the time it would take to do one clearance via voice, which improves taxi-out times and airport traffic flow. During severe weather, some aircraft have saved more than 90 minutes of delay time.
Performance Based Navigation (PBN)
From the mid-1940s to the turn of the 21st century, the ground-based Very High Frequency Omnidirectional Range (VOR) was the predominant navigational aid used by pilots. Distance Measuring Equipment (DME) is another common type of ground-based radio navigational technology. Yet reliance on infrastructure on the Earth's surface limits the availability of routes. Pilots using these navigation aids fly in a zigzag path, meaning that routes are less direct and more time-consuming.
In the 1980s, operators began equipping aircraft with the Flight Management System and computers featuring multiple navigation sensors. The enhancements, working with VOR and DME sensors, allowed computers to calculate a route between two arbitrary points without the aircraft flying directly over fixed stations on the ground. These routes used Area Navigation (RNAV) technology. When RNAV was introduced, aircraft flew routes that followed ground-based infrastructure, with accuracy varying greatly based on the aircraft's location relative to the navigational aid.
Positioning accuracy increased with the advent of GPS as a new navigation sensor. Specialists who designed flight paths could now create routes and procedures and specify aircraft performance without relying on ground-based navigational aids.
As GPS was included in the multi-sensor systems or as a stand-alone capability, Required Navigation Performance (RNP) was formed. RNP described how aircraft may fly an RNAV route or procedure using either ground-based or satellite-based navigation, as long as they can achieve the required performance. The required performance is directed when position accuracy is essential to separation, best use of airspace, and in some cases, obstacle clearance.
RNP requires aircraft to have on-board monitoring to ensure performance compliance and alert the pilots if the aircraft flies outside of a specified area. Pilots can fly reliable, predict- able, and repeatable procedures with tighter tolerances and constant radius turns.
PBN arose as a way to describe performance capabilities for RNAV and RNP. Both types of PBN allow equipped aircraft to fly shorter and more efficient flight paths, which reduce fuel consumption and engine exhaust emissions while improving schedule adherence. The FAA's concept of operations for PBN is to establish specified, repeatable flight paths where needed. We employ PBN for congested airspace, reduced or relocated ground navigational aids, or improved airport access.
Since 2015, PBN procedures and routes are the NAS standard during normal operating conditions. The FAA has published more than 9,600 PBN routes and departure, arrival, and approach procedures for more than 500 airports. Not all types of PBN procedures are suitable for every airport or phase of flight.
The FAA works with the aviation community to determine if a PBN procedure is worthwhile based on air traffic, airspace, airport, and community factors, as well as a cost-benefit analysis. Conventional procedures provide options to accommodate non-equipped users. The following examples show how PBN initiatives make a difference for pilots and aircraft operators.
In 2015, ELSO became a national separation standard for departing aircraft. ELSO allows controllers to space flight paths closer together and safely clear aircraft for takeoff more efficiently. This standard is possible because aircraft equipped for PBN can fly repeatable and predictable RNAV Standard Instrument Departures (SID).
RNAV SIDs provide fixed, repeatable paths for aircraft from takeoff to en route airspace with minimal level-offs. Standard flight paths simplify navigation tasks for pilots and controllers in all weather conditions without following step-by-step climb and turn instructions.
Low- and High-Altitude Routes
- The FAA is replacing conventional low- and high-altitude routes that used VOR navigational aids with PBN RNAV T-Routes for low altitudes and Q-Routes for high altitudes.
- The FAA is canceling many VOR-based "Victor routes" for GPS-enabled T-Routes for flight from 1,200 feet above ground level to 18,000 feet mean sea level. The FAA has published about 110 T-Routes.
- By 2030, all VOR-based "Jet routes" between 18,000 and 45,000 feet mean sea level will be cancelled in domestic airspace. Q-Routes, which derive positioning from either satellite signals or ground-based DME, will replace them. The FAA has published more than 160 Q-Routes.
Standard Terminal Arrival (STAR) with Optimized Profile Descent (OPD)
As flights descend from cruising altitude to an airport, aircraft traditionally level off at different altitudes as they are handed off from controller to controller or to deconflict the aircraft with other flights. These stair step-like descents consume more fuel as pilots need to increase engine thrust to maintain flight at the different altitudes.
STARs with an OPD have several advantages. Using the flight computer to program optimal speed and altitude requirements for various points along the route, aircraft can glide continuously at near-idle engine speed from the top of the descent to landing with minimal level-off segments. Aircraft can maintain higher, more fuel-efficient altitudes closer to the airport. Pilots can avoid using speed brakes and frequent thrust adjustments.
Established on RNP (EoR) Separation
At certain airports, air traffic controllers can use multiple parallel runways to increase arrival capacity. RNP approaches with a Radius-to-Fix leg allow for aircraft to approach their respective runway from the opposite direction of their eventual landing using a smooth curved path 180-degree "U-turn." EoR is the separation standard that allows for these aircraft to turn in on RNP or RNAV approaches simultaneously while other aircraft are conducting instrument approaches to a parallel runway. EoR separation makes flying more RNP or RNAV procedures easier, increasing PBN use and its benefits. These include shorter distance traveled, decreased fuel burn, reduced pilot-to-controller communications, more stabilized approaches, and more repeatable operations. The FAA approved EoR separation for widely-spaced parallel runways in 2015 and for simultaneous dual and triple independent approaches in 2018.
A metroplex is a metropolitan area with multiple airports and complex air traffic flows. Each metroplex involves a unique system of airports, aircraft, geography, and weather patterns. The optimization of airspace using PBN and publication of procedures in each metroplex are multi-year initiatives that provide major benefits in congested airspace near busy airports.
Study teams made up of air traffic controllers, pilots, airport operations, and technical staff analyze a metroplex's operational challenges and explore opportunities to improve operations. FAA teams engage affected communities on the scope of airspace modernization, considering the FAA's responsibilities under the National Environmental Policy Act.
The FAA chose 11 metropolitan areas for the Metroplex program in response to recommendations from the aviation community. Implementation is complete for nine of these areas and expected for Las Vegas and South/ Central Florida by 2022. Additionally, the FAA incorporated large-scale redesign of airspace for 29 busy airports not meeting Metroplex program criteria.
Automatic Dependent Surveillance-Broadcast (ADS-B) In and Out
The aviation community marked a turning point in its history on January 1, 2020: the FAA's ADS-B Out rule went into effect. It requires aircraft flying in most controlled airspace to be equipped with this more precise surveillance technology.
Air traffic controllers use surveillance technology to identify, monitor, and determine the position and altitude of aircraft for safe separation. Since the mid-20th century, radar technology provided controllers with this information. However, radar's limitations include a relatively slow refresh rate of between 5 and 12 seconds, compared to ADS-B. Geographic barriers also may limit where we install systems. Because its signals can be blocked by difficult terrain like mountains, radar sometimes leaves blind spots. Controllers must then apply less efficient separation between aircraft, or pilots fly without air traffic services.
ADS-B will eventually replace radar as the primary technology to track and separate aircraft. It uses GPS satellites and aircraft equipment to send information to ground stations, which then relay the information to controllers.
With ADS-B Out, aircraft broadcast their positions and other information every second. The improved accuracy and reliability of satellite compared to radar means controllers will be able to safely reduce the minimum separation distance between aircraft for non-radar airspace and increase capacity in the nation's skies. A network of nearly 700 ADS-B ground stations supports this aircraft surveillance technology.
ADS-B In enables equipped aircraft to receive broadcasts on air traffic, flight, and weather information at no additional cost to operators, improving access to safety information for pilots in flight. ADS-B In is not required by the mandate.
Decision Support System (DSS) Automation
NextGen automation systems like DSSs organize and increase the visibility of aviation information. Three decision support hardware and software systems enable controllers, traffic managers, and other stakeholders to quickly and efficiently respond to evolving traffic and weather conditions. The DSSs improve common situational awareness through real-time information sharing. Each DSS has a specific role and together provide an integrated, responsive, and collaborative way to manage traffic flow. DSSs maximize efficiency, balance demand to capacity, and reduce delays through each phase of flight. Aircraft operators and passengers benefit from more orderly taxiing and flexible airspace routing, which leads to smoother, faster, and more cost-efficient flights. The following three systems allow controllers to work more productively by ensuring safety and enabling more collaboration.
Traffic Flow Management System (TFMS)
TFMS, the NextGen version of the legacy Enhanced Traffic Management System, can predict air traffic volume, gaps, and surges based on current and anticipated airborne aircraft at local and national levels. Traffic managers at the FAA's Air Traffic Control System Command Center use TFMS tools to model and implement strategic traffic management initiatives across the NAS, maximizing the use of available capacity and minimizing delays. TFMS mitigates issues that require proactive planning, coordination, and adjustments, such as poor weather. Such mitigation is needed to lessen negative consequences of these constraints, which include delays, missed connections, canceled flights, and increased fuel consumption. When delays are unavoidable, TFMS allows each flight operator to submit the best route options and substitute flights to satisfy business objectives for their scheduled aircraft, for example, to ensure more passengers are on time to catch connecting flights.
Time Based Flow Management (TBFM)
TBFM uses time instead of distance to schedule and sequence aircraft. Compared to the miles-in-trail process for sequencing aircraft, in which controllers assign additional distance measured in miles between aircraft, TBFM provides a more efficient flow that reduces fuel burn, lowers emissions, and increases throughput.
TBFM, evolved from the legacy Traffic Management Advisor, is a system for planning flight trajectories through cruise altitude to the terminal approach airspace. Air traffic controllers can better regulate traffic by directing each aircraft to specific locations at a designated time. TBFM can sequence and schedule aircraft, taking into account aircraft types and flight characteristics. It maximizes throughput at select busy airports and terminal radar approach control (TRACON) facilities without compromising safety. The system operates at 20 en route centers.
TBFM departure management tools include:
- Integrated Departure/Arrival Capability (IDAC), which automates the process of monitoring departure demand, identifying departure slots, and assigning them to aircraft. The tool coordinates departure times between airports and informs air traffic control towers so they can select from available departure times and plan their operations to meet those times. IDAC uses electronic messaging rather than a telephone call from the tower to the en route center to request a departure time.
- Using IDAC automation, En Route Departure Capability (EDC) helps determine how long to delay a flight departure and where it will fit in the overhead stream. EDC helps to manage a miles-in-trail restriction, when controllers require additional spacing between flights to manage congestion in another part of the country.
TBFM arrival management tools include:
- Time-Based Metering, which delivers aircraft to a specific point at a specific time. It allows air traffic controllers to manage aircraft in congested airspace more efficiently by smoothing out irregularities and delivering a more consistent flow of traffic.
- Adjacent Center Metering and Extended Metering, which take the metering capability beyond a single center's airspace. Aircraft can absorb delays by reducing cruise speed at more fuel-efficient altitudes to meet their scheduled time of arrival.
- Ground-Based Interval Management–Spacing (GIM-S), which is an interface between TBFM and ERAM that calculates speed advisories. Using GIM-S, an air traffic controller can put each aircraft at the correct time and place to initiate an OPD more than 100 miles away from airports that support this PBN procedure. Aircraft improve fuel efficiency by absorbing delays at higher altitudes instead of excessive step-by-step radar vectors for spacing closer to the airport.
Terminal Flight Data Manager (TFDM)
TFDM provides capabilities to manage surface operations and flight data at airports. This system results in four objectives: improved electronic flight data distribution and electronic flight strips in the tower; collaborative decision-making on the airport surface; traffic flow management integration with TFMS and TBFM; and systems consolidation. TFDM includes the functions of and replaces these tower systems: the Electronic Flight Strip Transfer System, Airport Resource Management Tool, Surface Management Advisor, and Departure Spacing Program.
In June 2016, the FAA awarded a contract to develop and deploy TFDM. A number of precursor applications and testing of capabilities paved the way for better decision support tools for control towers and TRACON facilities.
Advanced Electronic Flight Strips (AEFS) was the first prototype system of its kind in the NAS. Electronic flight strips allow tower controllers to view a full route, including departure fixes and Data Comm departure clearances.
This technology is especially beneficial to controllers and air carriers when severe weather hits and changes to flight plans occur frequently. With AEFS, controllers can update flight information with the swipe of a finger or the click of a mouse. Controllers no longer need to print new strips and physically carry paper flight strips across the control room.
The AEFS function, which the FAA has implemented in towers at Charlotte Douglas (CLT), Cleveland Hopkins (CLE), and Phoenix Sky Harbor (PHX) international airports, will be incorporated in the production TFDM system.
The Surface Visualization Tool (SVT) shares situational awareness of the airport surface for traffic management coordinators. Controllers at terminal radar approach control facilities can easily identify departure congestion and anticipate changes — such as switching runway operations in response to a shift in wind direction — as if they were in a tower.
In 2017, the FAA enhanced SVT to include traffic flow management data, specifically gate assignment information that certain air carrier partners provide. SVT operates at 16 air traffic facilities to support early implementation of TFDM capabilities. The functions of SVT will be incorporated into and enhanced with deployment of TFMS.
Integrated Arrival/Departure/Surface (IADS) Traffic Management improves the efficiency of surface operations at the nation's busiest airports through time-based metering of departures and improved sharing of flight operations information among various stakeholders.
Working with the FAA and industry on Airspace Technology Demonstration 2 (ATD-2), the National Aeronautics and Space Administration (NASA) is demonstrating the concept of an IADS capability that makes use of increased information sharing between the FAA and industry. The capability will deliver improved predictability and efficiency for scheduling and metering flights from airports.
At Charlotte Douglas International Airport (CLT), ATD-2 Phase 1 introduced the tools and folded in the participation of the FAA's air traffic control facilities. Phase 2 expanded the scope of the demonstration to include Atlanta en route center and new technical capabilities. Phase 3 focuses on coordinating air traffic departing from Dallas/Fort Worth International Airport (DFW) and Dallas Love Field (DAL).
The two airports represent the broader challenge of managing air traffic over metropolitan areas with multiple airports close together. Phase 3 began in October 2019 and will continue through September 2020. ATD-2 achieves the vision of the capabilities described in the concept of operations planned for the TFDM system. NASA has been transferring ATD-2 capabilities, benefits, and lessons learned to the FAA and industry to improve information sharing for our DSSs and enhance collaborative decision-making.
These technologies will increase predictability in the air traffic system and enhance operational efficiency while maintaining or improving capacity. This process will lead to reduced environmental effects and better coordinated scheduling across the NAS.
TFDM development began in 2017 and will begin operating in Phoenix in 2020; 88 more sites are set to be completed by 2028. All 89 sites will feature electronic flight strips and 27 locations will have surface time-based management capabilities.
System Wide Information Management (SWIM)
SWIM is an information-sharing application that delivers the right information to the right people at the right time with far less expense and complexity than legacy methods. Before SWIM, the FAA primarily shared data through dedicated point-to-point computer connections and via radio, telephone, and the internet. With these conventional methods, everyone could not see the same information at the same time. This hard-wired infrastructure also could not readily support more data, systems, users, and decision makers.
Today, 11 FAA programs and six external organizations produce data for 80 services sent via SWIM. More than 400 consumers are registered to access the information, and the availability of data has created a new information ecosystem. Companies are using information derived from SWIM to develop innovative applications for the aviation community.
SWIM promotes situational awareness and more accurate aeronautical, weather, and flight information. It is beneficial because of its common data format, which allows for collaboration between the aviation community and governments worldwide. SWIM increases efficiency by allowing stakeholders to share current, relevant, reliable, and consistent information on demand, allowing for faster responses to changes in weather, traffic, and other factors. It eliminates the need for multiple computer interfaces to access data from different sources. With this new method, data producers publish the information once and subscribers access information through a single connection.
SWIM serves these types of consumers:
- The FAA, Department of Defense, and other government agencies
- Airlines that depend on SWIM for daily operations
- Large companies turning data into services for airlines
- Entrepreneurs seeking to develop innovative applications
- Foreign air navigation service providers
- Organizations or universities researching and developing future FAA programs
The FAA started SWIM in 2007 and has incrementally deployed applications as they became available. These features are examples of how SWIM is improving NAS operations.
SWIM Terminal Data Distribution System (STDDS)
STDDS converts raw surface and terminal surveillance data received through ADS-B, radar, or multilateration sensors into the extensible markup language, or XML, format. This format is near universal and can be easily combined into almost any application, allowing seamless data transfer now and into the future. STDDS uses the NAS Enterprise Messaging Service to send surface information from airport towers to the corresponding TRACON so traffic management coordinators can assess how to best balance demand with capacity. The FAA installed STDDS at 38 TRACONs that pulls information from 150 airports. The data is available to both internal and external NAS information consumers.
A new STDDS software release in 2019 enabled more data sharing.
Runway visual range is one of six sources from which STDDS publishes data. This tool measures horizontal distance a pilot can see on the runway. Runway visual range is one of many legacy feeds that have switched to SWIM, and this data under SWIM has grown from 60 to more than 130 airports. It is expected to eventually serve 200 airports.
SWIM Cloud Distribution Service (SCDS)
SCDS enables the FAA to meet the needs of more users and more data flowing through the system. The cloud provides real-time, non-sensitive SWIM data to the public, including access to the same publicly available data offered via the NAS Enterprise Service Gateway.
A secure connection forwards approved data from the gateway to a commercial cloud provider using FAA Cloud Services. Instead of waiting at least 6 months to access data through the old registration and distribution process, the cloud enables a user to tap into tailored data within 72 hours of a basic online account setup. Operating costs are lower, and the new service adjusts bandwidth to support data flow.
NextGen Weather harnesses massive computing power, unprecedented advances in numerical weather forecasting, translation of weather information into airspace constraints, and modernized information management services. With this powerful combination, NextGen Weather can provide tailored aviation weather products within the National Airspace System, helping controllers and operators develop reliable flight plans, make better decisions, and improve on-time performance.
The flying public will experience less weather delay, including fewer departure and arrival delays, reduced number of flight cancellations and refueling stops, and overall increased dependability in flight schedules. Learn more here about the different components of weather.
Not all NextGen improvements need expensive infrastructure. Sometimes research leads to new FAA policies, procedures, and standards that improve efficiency or increase capacity.
Wake Recategorization (Wake Recat)
A plane flying too close behind another is at an increased risk of a potentially dangerous encounter with wake vortex turbulence. To reduce wake-related hazards, controllers traditionally separated aircraft based on wake separation standards set on their maximum certified gross takeoff weight. Although safe, these separation standards did not take into account other aircraft characteristics, such as speed and wingspan. Research provided better data on the strength of the wake and an aircraft's reaction to turbulence generated by aircraft in front of it. It provided an opportunity to generate new standards. Wake Recat can increase airport capacity, which means more aircraft can take off and land, reducing arrival delays and wait times on taxiways and runways. The FAA is planning to deploy consolidated wake turbulence standards to all airports in the coming years to further enhance efficiency.
Expanded Low Visibility Operations (ELVO)
ELVO is a low-cost infrastructure program designed to reduce ceiling and runway visual range minimums through a combination of ground equipment and procedures. It addresses limitations of low visibility and poor weather and has allowed aircraft to operate at airports during inclement weather when they would have previously not been able.
As part of ELVO, the FAA published rules authorizing use of different Enhanced Flight Vision Systems (EFVS). Imaging sensors and a display to identify required real-time visual references outside of the airplane. Synthetic systems create a virtual depiction of these conditions. Pilots can use EFVS in many types of cloud cover to meet visibility requirements for certain types of departures and arrivals.
A 2015 FAA assessment showed access during low-visibility conditions of airports studied improved in two ways, in part, because of ELVO: no-access periods decreased by about 6 percent and 17 percent more flights could land.
Because the benefits of new capabilities must align with the safe operation of the NAS, all new capabilities are implemented only after thorough safety testing. The FAA conducts NextGen-unique safety risk management for research and development, prototyping, testing and evaluation, and flight trials and demonstrations. We incorporate risk-based decision-making to support agency-wide safety initiatives. Along with resources, such as the Hazard Identification, Risk Management, and Tracking Tool; the Aviation System Information Analysis and Sharing; and the System Safety Management Transformation, program teams can access centralized data to provide a holistic perspective on system risks. The NextGen Safety Management System emphasizes safety management as a fundamental business process that we must place with the same high priority as other important organizational functions.
Environment and Energy
The FAA shares research and development costs to make environmental investments more attractive to our industry partners. The work supports a NextGen goal of reducing the environmental impact of aviation while sustaining growth. The aviation community is working together with FAA to develop alternative fuels and certifiable aircraft and engines that produce less noise and emissions and increase fuel efficiency.
New Aircraft Technologies and Alternative Jet Fuels
The Continuous Lower Energy, Emissions, and Noise (CLEEN) program is the FAA's main environmental effort to accelerate the development of new aircraft and engine technologies and advance sustainable alternative jet fuels.
Technologies matured during CLEEN's 2010– 2015 phase will reduce fuel consumption by 2 percent from 2025 through 2050 across the domestic fleet, according to research conducted at the Georgia Institute of Technology. This figure is equivalent to saving 22 billion gallons of jet fuel; the reduction in carbon dioxide emissions is comparable to removing 1.7 million cars from the road. CLEEN will save airlines $2.75 billion per year and contribute to a 14 percent decrease of geographical areas exposed to noise.
Alternative jet fuels are another element of the FAA's strategy to take on aviation's environmental and energy challenges. These resources can replace petroleum-derived jet fuels without the need to modify engines and aircraft. We are now focusing on testing the safety of these alternative fuels and analyzing processes to understand benefits, production potential, and challenges to establishing supply. Since 2006, the FAA has worked with the alternative jet fuel stakeholder community through CAAFI, the Commercial Aviation Alternative Fuels Initiative. We also are partners with other federal agencies, universities, and research institutes to accelerate testing of alternative jet fuel required for certification. These efforts happen largely through CLEEN and the FAA Center of Excellence for Alternative Fuels and Environment.
Unleaded Aviation Gasoline
Leaded aviation gasoline used to fuel piston engine aircraft is the largest contributor to the relatively low levels of lead emissions in the United States. The FAA William J. Hughes Technical Center is researching suitable alternatives. We originally hoped for a fuel replacement that would not require modifications to existing engines, but extensive research determined it was not feasible. In response, the FAA started investigating ways to lessen the impact of implementing replacement fuel on the general aviation fleet and on manufacturing and distribution infrastructure. Once a suitable unleaded alternative is approved, the FAA and the aviation community will collaborate to safely transition to this new fuel.