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From Shrimp Boats to Satellites

The Evolution of the National Airspace System

FAA Safety Briefing
Cleared for Takeoff
9 min readAug 31, 2021


By Tom Hoffmann, FAA Safety Briefing Managing Editor

Photo of TRACON.

It’s a sweltering summer afternoon in 1929 at St. Louis Lambert Field. Peering out from under the shade of a beach umbrella perched alongside the airport tarmac, mechanic and barnstormer pilot Archie League carefully scans the sky. While manning his makeshift control tower — a wheelbarrow — League patiently waits to direct aircraft to and fro with a pair of signal flags at the ready. It is hard to imagine, but in the late 1920s this crude operation represented the extent of air traffic control services.

Historical photo of Archie League.
Pioneer air traffic controller Archie League.

League’s efforts as a pioneer air traffic controller, while venerable, stand in stark contrast to how air traffic control (ATC) keeps aircraft safely separated today. More than 90 years later, today’s National Airspace System (NAS) is among the most complex in the world, supporting roughly 5,000 aircraft traversing the skies at any given moment during peak periods (pre-pandemic) and more than 19,000 airports across the nation. At the heart of those operations are the 14,000-plus air traffic controllers who work in concert with a vast network of navigational equipment to keep our skies safer than they have ever been. That is no small accomplishment given the numerous changes the aviation industry has experienced over the last century. As we continue to embrace the safety-enhancing benefits of the FAA’s Next Generation Air Transportation System initiative, there is much we can learn from previous generations whose innovative thinking enabled them to adapt to changing environments and affect safe change in the NAS.

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Can You Hear Me Now?

According to early airspace pioneer Glen Gilbert, air traffic control has one basic objective: to prevent a collision between two aircraft. That simple creed became increasingly difficult to uphold with the voluntary “see and be seen” policies in place during aviation’s early 1930s boom. Gilbert was among the first to emphasize the need for not only a more structured system, but also one that mandated participation to remain effective. One of the limiting factors at this stage was radio technology, which, as its popularity grew, eventually phased out the bonfires, signal flags, and light gun signals previously used as communication tools. Direct radio links also proved useful as they would later replace the cumbersome relay of one-way telephone and radio calls among the pilot, dispatcher, and controller.

Further complicating the early days of ATC was the lack of engineering support from the U.S. Department of Commerce. This meant controllers had to be inventors as well as guardians of the sky. Early home-grown ideas that helped controllers perform their jobs included telephone recording equipment, flight sequencing boards, and small wooden markers dubbed “shrimp boats” that were pushed around an airspace map every 15 minutes to keep track of aircraft positions.

Since the science of airspace management was literally starting from scratch, there was also a pressing need for system planning contributions. Earl Ward, regarded by many as the father of air traffic control, is credited with many of those innovations. Ward conceived the idea of establishing a system of Air Traffic Control Centers. The first three were located in Newark, Cleveland, and Chicago. These centers, along with the procedures Gilbert helped develop for the industry’s first ATC manual, provided the building blocks for what was becoming a globally recognized air traffic management system.

In the years that followed, aviation continued to grow, spurred by World War II efforts to build more airports and produce bigger, faster, and more advanced aircraft. While some may have questioned the ability of U.S. airspace to accommodate the anticipated gridlock of private, commercial, and military users, Gilbert maintained that an ATC system should not discriminate but permit access to all categories of airspace users. He dispelled the notion of what were considered “incurable limiting factors” in his book Air Traffic Control: The Uncrowded Sky. “It is the system that is crowded, not the skies,” said Gilbert. “In other words, our objective must be to learn how to effectively utilize the virtually unlimited capacity of our Uncrowded Sky.”

The advent of radar technology helped do just that, and by the early 1950s, aircraft movements were now visible on electronic scopes. Aided later by computers, ATC was soon able to follow those blips on more sophisticated three-dimensional tracks. In the following decades, airspace safety made tremendous strides with enhancements in the areas of automation, weather, navigation, avionics equipment, and more. These improvements became effective tools in handling the growing volume and diversity of traffic and provided both ATC and pilots greater situational awareness, a key ingredient to a safe NAS.


Gilbert maintained that an ATC system should not discriminate but permit access to all categories of airspace users.

Recalculating …

Gilbert had the right idea when he predicted the final challenges for a future generation of effective air traffic management would be the need to factor in the complete picture of all its individual elements. That means considering everything from the framework of regulations and procedures to the end-user pilots and controllers. Based on principles of integration and collaboration, the FAA’s satellite-based NextGen transition takes a more holistic approach to airspace safety and represents an entirely new and forward-looking way of doing business.

A cockpit display.

In 2021, the impact of NextGen is clearly visible with NAS users who regularly reap its many benefits. Setting the stage for today’s capabilities were accomplishments focused on the Automatic Dependent Surveillance-Broadcast (ADS-B) system. One of six transformational NextGen technologies, ADS-B transmits the location of aircraft to controllers and other ADS-B equipped aircraft with a faster update rate than radar. Aircraft equipped with ADS-B In avionics can receive traffic information, enhancing pilot situational awareness. Aircraft able to receive signals on 978 MHz can also receive weather and aeronautical information in the cockpit. Pilots flying in properly equipped aircraft in ADS-B coverage areas can also see the location of surrounding aircraft that are equipped with ADS-B or transponders in a 15-mile radius, 3,500 feet above or below their current altitude. The nationwide infrastructure for ADS-B was completed in 2014. This means that the nation’s airspace system now has satellite-based coverage wherever radar coverage exists — as well as in some areas that lack radar coverage, such as certain low-altitude airspace, the Gulf of Mexico, and Alaska. Real-time ADS-B is also the preferred method of surveillance for air traffic control in the NAS.

We are now one and a half years beyond the ADS-B Out equipage mandate for those operating in designated airspace and, as of July 1, 2021, over 146,000 U.S. aircraft have been properly equipped. You can read more about the benefits and capabilities of ADS-B at

Another critical component of NextGen is Data Communications, or Data Comm, which is a digital communications platform that uses electronic messages between pilots and controllers. Digitally delivered clearances have already improved accuracy by eliminating misheard communications and confused call-signs, and reducing radio congestion. Data Comm is currently operational at 62 control towers and three Air Route Traffic Control Centers in the United States, with more on the way.

The NextGen initiative is nearing completion. While there is still some way to go to realize its full potential, the growing frequency of NextGen success stories is a sure sign that it has made a lasting impact on the safety of the NAS.

Sharing the Skies

Photos of drones or UAS.

Despite recent uncertainties on COVID 19-related slowdowns and their long-term impact on the economy, the FAA’s latest Aerospace Forecast projects that operations at FAA and contract towers will grow, albeit modestly, at 0.9% per year over the next 20 years, with commercial and business aviation as the primary drivers. In addition to this regular growth, NAS users are also learning to share the skies with new entrants. Developing at breakneck speeds are the many commercial applications of Unmanned Aircraft Systems (UAS) or drones, ranging in size from a small bird to a medium-size airliner.

With the newly published Remote Identification and Operations Over People rules, the FAA has taken a giant leap towards expanding NAS integration efforts and allowing for more routine operations for certain small UAS, all without compromising safety. This includes operations that are beyond visual line of sight (BVLOS). A newly formed UAS BVLOS Aviation Rulemaking Committee is further exploring this concept and aims to provide recommendations for performance-based regulatory requirements to normalize safe, scalable, economically viable, and environmentally advantageous UAS BVLOS operations that are not under direct air traffic control. A first report is expected by early 2022.

Whether using bonfires, shrimp boats, or high-tech satellites, the FAA’s mission has always focused on providing the safest, most efficient aerospace system in the world.

Taking NAS Operations to New Heights

Chart showing commercial space launches.

Another rapidly expanding area is literally out of this world. The FAA’s Office of Commercial Space Transportation, which licenses and regulates U.S. commercial space launch and reentry activity, recently recorded its 400th commercially licensed launch and is forecasting the number of commercial space operations to meet or exceed 50 in 2021. It’s possible that number could reach 100 or more per year in the not-too-distant future once space tourism really takes off. So far, the FAA has also issued licenses for 12 commercial spaceports located in six states, with six additional spaceports in the process of obtaining a safety approval. To bolster support in this arena, the U.S. Department of Transportation (DOT) recently renewed a charter with the Commercial Space Transportation Advisory Committee (COMSTAC) to extend to June 2023. This 22-member committee provides valuable input to DOT and the FAA on space operations, including expert advice on safety and technology.

Another exciting chapter in the evolution of the NAS involves the growing advancement of Unmanned Aircraft System Traffic Management (UTM) as well as Advanced and Urban Air Mobility (AAM/UAM). The latter is a developing ecosystem of transportation that envisions the use of highly automated aircraft that transport passengers and cargo in urban and suburban areas, and includes longer range operations for both commercial and recreational purposes. The cornerstone for the type of situational awareness required for these operations to be safely performed is UTM. You can read more about these game-changing concepts in our May/June 2021 “Sharing the Skies Safely” issue or at NextGen’s open and collaborative approach towards problem-solving is designed to effectively factor in these and other challenges that might arise during the next phase of airspace evolution.

You Are Cleared for the Approach

To say the nation’s airspace has witnessed a tremendous amount of change over the last century would be quite an understatement. Whether using bonfires, shrimp boats, or high-tech satellites, the FAA’s mission has always focused on providing the safest, most efficient aerospace system in the world. Even in the early days of airspace development, we can see the great deal of planning, coordination, and outside-the-box thinking needed to overcome challenges and maintain safety in the NAS. Those same principles are alive and well today and are among the key tenets of NextGen, a model of safety and efficiency that promises access to all categories of users. That’s something the founding fathers of ATC would surely be proud of today.

Tom Hoffmann is managing editor of FAA Safety Briefing. He is a commercial pilot and holds an A&P certificate.
This article was originally published in the September/October 2021 issue of FAA Safety Briefing magazine.
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FAA Safety Briefing
Cleared for Takeoff

Official FAA safety policy voice for general aviation. The magazine is part of the national FAA Safety Team (FAASTeam).