Five years ago, the FAA set out to revolutionize air traffic control. Their comprehensive plan failed to attain airspeed-will an incremental approach fly before aerial gridlock sets in?
Birds do it. Bees do it. Even Orville Wright did it. Why can’t today’s pilots do it too?
“It” is “free flight,” an alluring notion thrust into official awareness by a passionate group of pilots and researchers in the mid-1990s. Free flight, these advocates argued, would transform aviation from, well, the ground up. The idea sounded simple and intuitive, and at the same time radical: Free pilots from the rigid, circuitous routes imposed by ground-based air traffic control, and let them choose the quickest and most fuel-efficient paths around wind and weather. New satellite, computer and communications technologies would keep aircraft from crashing into one another. Planes would fly faster, cheaper and even more safely, avoiding the gridlock that currently threatens the overloaded air traffic system.
Today, five years after Congress validated this vision and the Federal Aviation Administration (FAA) set out to realize it, free flight is still sitting on the runway. Air traffic is more congested, more delay-prone and scarcely any freer. “The whole idea of free flight’ has kind of fizzled,” says Heinz Erzberger of NASA’s Ames Research Center, the lead scientist in the development of a more limited air traffic automation scheme now coming into use. The FAA and its constituents have retreated from a comprehensive free-flight agenda (what some critics call the “Big Bang” approach) to limited demonstration projects and incremental improvements.
For some, this retrenchment marks a welcome return to reality. For others, it is a temporary obstacle to clearance for takeoff. But for some of free flight’s radical devotees, it’s an unconscionable retreat from an urgent and eminently feasible mission, the latest in a string of costly botches and compromises by the FAA. And since there are no alternative proposals on the table for a substantial overhaul of the air traffic control system, some experts think were on course for a nightmare in the sky.
“We’re currently number ten for takeoff…”
Father figure: Many credit Bill Cotton with the idea of free flight.
Though observers of airline traffic don’t agree on much, they all concede that the existing system must be improved. With about 21,000 commercial flight departures each day, a number variously projected to grow by 2 percent to 5 percent a year, air planners have moved from lamenting congestion to invoking the dreaded “G” word.
“Gridlock is near,” the National Civil Aviation Review Commission intoned in a 1997 report titled, perhaps ironically, A Consensus for Change. “Traffic data and trends indicate that adding just a few minutes of delay to each airline flight in the United States will bring the aviation system to gridlock with dramatic negative impacts on the economy,” not to mention alarming “safety implications.” Delta Airlines, to name one example, has warned that even such relatively small additional delays will mean it can no longer function as a scheduled airline.
Meanwhile, despite repeated, costly modernization efforts, the outdated, overloaded air traffic control system is straining to keep up. Again and again, aircraft simply “disappear” from controllers’ radar screens; last year, Air Force One vanished twice. To compensate for such lapses, controllers must increase safety margins by boosting separation distances and holding planes back. That has kept the accident rate in U.S. commercial aviation stunningly low. But according to the man often called “the father of free flight,” pilot-turned-airline-manager William B. Cotton of United Airlines, that record comes at a price: “Safety has always been maintained at the expense of capacity and efficiency.”
Although the system is straining to the breaking point, it is still remarkable that it works as well as it does, given the way it’s grown. For 40 years, functions, hardware and software have been mixed, matched, replaced and added in, forming a massive patchwork.
Today, controllers guide pilots verbally through each turn, climb, descent, acceleration and deceleration-from takeoff to landing-using only radar tracking and radio communications. Each controller in the FAA’s en-route centers monitors a sector that may be several hundred kilometers wide, with as many as 20 planes crossing at a time.
Limiting planes to preset routes across each sector helps the controller track and negotiate traffic. This is critical, because controllers must perform time-and-distance calculations in their heads. But preset routes add turns and miles, wasting fuel. And “handing off” flights from one controller’s sector to another’s creates opportunities for potentially dangerous errors, and for delay-inducing logjams when volumes climb (as they have recently with the surge in short-haul regional jet operations).
Even when this system was new, a few upstart innovators were thinking about making it better. Among the first was Cotton, now United Airlines’ Air Traffic and Flight Systems manager. In 1965, in his MIT master’s thesis, Cotton proposed that, instead of relying on ground instructions, planes could maintain flight separation through automatic air-to-air communication, with cockpit displays of the data they exchanged. At the time this scheme was a dream, since the technology to implement it didn’t exist. More than three decades later, these ideas would become essential elements of the FAA’s own free-flight concepts.
In the Zone
Cotton’s vision, which he refined over the years, was built around the concept of safety “zones.” Each plane would maintain two electronic surveillance zones: an inner “protected zone” around itself, nestled in a larger “alert zone” spreading out in front. To keep the protected zone inviolate, any overlap of alert zones would send a warning, prompting course corrections and restrictions.
An early step toward implementing the concept of Cotton’s zones was the Traffic Alert and Collision Avoidance System (TCAS), which grew out of collision-avoidance logic developed by Bendix in the 1950s. Required on all U.S. passenger aircraft since 1993, TCAS sends radio signals that, when returned by other planes’ transponders, inform the system of those planes’ approximate bearings and altitudes. It scans these data for prospective collisions and advises the pilot to climb, descend or stay steady.
Subsequently modified to prevent false alarms, TCAS has proved to be a lifesaving backup to traffic control and navigation. It has also been seen as a possible tool for realizing the tantalizing notion of free flight.
Indeed, it was TCAS that brought two of the key players in today’s free-flight debate together-before driving them apart. United pilot R. Michael Baiada had worked on navigation technologies as an engineer at Bendix and on proto-free-flight efforts as a manager at a small airline. In 1987 he signed on at United under Cotton to help test TCAS.
Baiada’s Bare Bones
As the official version of free flight lumbered toward takeoff, one of its champions-Baiada-was growing more and more impatient. The problem, he decided, was not too little technology, but too much reliance on new, unnecessary and unaffordable technologies.
Baiada argues vehemently that while GPS, datalink and other avionics can make flight more efficient, they aren’t essential to free flight. And by making the move to free flight much more protracted, complicated and costly, they effectively keep it from happening.
By contrast, Baiada proposes a starkly heretical “minimalist” approach to free flight. All it takes, he argues, is adding two software capabilities to existing ground-based computer systems. One, called “conflict probe,” would automate system-wide much of what human controllers now do in fragmented, sequential fashion in their individual sectors. While pilots and air dispatchers made or changed flight plans at will, the software would compare the plans with radar data, alerting controllers to any possible collisions between flights within the next, say, 10 or 15 minutes. Controllers would track flights as they do now, but only intervene to resolve such conflicts.
The other element of Baiada’s minimalist scheme is “time-based sequencing” at the arrival end. This software would automatically determine each plane’s place in the landing queue-one of the many operations controllers now perform in their heads. Not only would this make the stream of traffic on the runway more steady, it would also give each flight a precise landing slot to aim for. This would enable pilots to pace themselves and stay at higher altitudes (where planes are more fuel-efficient) until the last minute, rather than descending and then having to wait to land.
One thing that particularly galled Baiada was that he believed the FAA already had these tools and wasn’t taking advantage of them. In particular, Baiada wanted to see the agency implement a piece of conflict-probe software developed by FAA computer scientist Norman Watts and contractor Lonnie Bowlin. The software impressed some FAA researchers, managers and controllers, but after testing it at the Boston en-route center in 1995-96, the agency decided to go with a product from Mitre instead.
By then, Baiada had already left his post under Cotton (though he continues to fly for United). He started waging his free-flight crusade in op-eds for the aviation press, conferences and every other forum he could find. Today, Cotton dismisses him as “a stonethrower” who’s burned too many bridges to be effective. Baiada insists that stonethrowing was the only way to get any action.
Free Flight Lite
While Baiada waged his lonely crusade, the FAA’s Flight 2000 scheme crashed and burned, thanks to lack of industry (and, consequently, congressional) support. Now two projects, each on a much smaller and more conservative scale, are rising from the failed plan’s ashes (see “The Technologies Behind Free Flight” table). Ironically, each one puts into practice the ideas of one of the two allies-turned-antagonists, Cotton and Baiada.
One of the two current efforts, known as Safe Flight 21, incorporates two trials of the avionics approach pioneered by Cotton. In a slice of the original all-Alaska test bed, small planes-which fly outside of ground control-will use the Flight 2000 technologies in an attempt to improve safety. Safe Flight 21’s other component tests the same avionics in an interesting new sector: air cargo companies.
Because cargo companies haven’t had to install TCAS (as passenger carriers have), they are particularly interested in one technology under study in Safe Flight 21 that might provide an even better collision-avoidance solution: Automatic Dependent Surveillance Broadcast, or ADS-B. This system transmits position, identification, velocity and direction information from cockpit to cockpit and cockpit to ground. And it doesn’t hurt that United Parcel Service (UPS) has backed the project as both a user and supplier of the new technology: Its subsidiary UPS Aviation Technologies makes the ADS-B units being tested.
ADS-B performed well in initial Safe Flight 21 tests this summer. And though ADS-B hasn’t yet been proven as an avoidance system, UPS Airlines spokesman Ken Shapero is confident it will be: “Eventually, passenger airlines will want ADS-B for collision avoidance. It’s like digital versus analog cellular phones.”
By leapfrogging over TCAS (an analog system with relatively short range) to digital, wider-range ADS-B, with its richer store of data, the carriers hope to get collision avoidance and much more. How much more? Maybe free flight, someday; UPS is driving to make ADS-B free flight’s base technology. “If we get the technology in place, then we can figure out applications,” argues Shapero. “The FAA failed with some Big Bang programs for which no technology existed, then tried to make the technology work.”
The other current free flight initiative, Free Flight Phase 1, is a streamlined approach that happens to follow the same principles Baiada urges-act now, without waiting for any more newfangled technologies to come online. This scheme was prompted partly by the failure of the grander free-flight scheme. In mid-1998, the FAA was desperate to chalk up a success and show its commitment to modernization under a new administrator, Jane Garvey. “The industry and the agency got together and realized they needed to bring out something quicker, sooner, better,” says Free Flight Phase 1 assistant manager Robert Voss, echoing NASA’s “faster, better, cheaper” mantra.
Thus was Free Flight Phase 1 born in July 1998, with a substantial budget but a mission that seemed drafted to defuse fears of over-reaching: “To introduce modernization into the national air system incrementally-taking a building block approach to fielding new systems to provide benefits to users as soon as possible.” Forget the fancy avionics; Free Flight Phase 1 would deploy software capabilities already available or in development to streamline ground-based control.
The Technologies Behind Free Flight
Technology Function Source Included in Safe Flight 21: Automatic-Dependent Surveillance Broadcast (ADS-B) Improved separation, “see and avoid,” taxiway navigation, surveillance in nonradar air space, perhaps collision avoidance UPS Aviation Technologies Datalink transceiver Digitized radio communications Honeywell, UPS Aviation Technologies, or Aviation Data Systems Innovation Traffic Information Services-Broadcast (TIS-B) Broadcasting traffic, weather, and other data from the ground to the cockpit Undetermined; planned for year 2000 Cockpit Display of Traffic Information (CDTI) Displays ADS-B and TIS-B data, controllers’ instructions UPS Aviation Technologies Global Positioning System (GPS) Navigation, location UPS Aviation Technologies (receivers) Digital terrain database with moving map Crash avoidance UPS Aviation Technologies Included in Free Flight Phase 1: Center-TRACON Automation System (CTAS) Suite of automation tools for airport-approach and en-route control centers NASA Ames Research Center User-Request Evaluation Tool (URET) Conflict probe Mitre Collaborative Decision Making (CDM) Real-time exchange of scheduling data and changes by airlines and air space managers More than 50 airlines, federal agencies, universities, research and industry organizations participating Controller-Pilot Data Link Communications (CPDLC) Limited ground-air digital communications FAA Surface Movement Advisor (SMA) Provides airlines with aircraft arrival information for better runway routing FAA
Is Half a Cheer Better Than None?
Free Flight Phase 1’s “free flight lite” approach and the pared-back avionics trials of Safe Flight 21 get cheers from the airlines, who have long pitched for such closely focused, cost-conscious approaches, and the traffic controllers, who are relieved that neither program threatens to eliminate their jobs. But free flight early advocates give perhaps only half a cheer. “They’re starting to implement free flight,” Cotton says, “but much too slowly.” Baiada actually agrees with Cotton on this point: “Free Flight Phase 1 would have been a good program-20 years ago.”
Indeed, the three-year Free Flight Phase 1 program is neither breaking new technological ground nor implementing system-wide improvements. “It’s just another R&D effort,” laments Michael Goldfarb, a former FAA chief of staff who’s now in private consultancy. “They’re spending hundreds of millions on disparate things, none of which talk to each other,” Goldfarb says. “The FAA hasn’t figured out the concept of operations.”
For his part, Baiada remains adamant that a stripped-down scheme, using only conflict probe and time-based sequencing, could achieve 70 percent to 90 percent of free flight’s eventual efficiency in just “three to five years.” All it would take, Baiada says, is a $500 million investment in off-the-shelf software to be installed in the current infrastructure. And again, the software he believes to be capable of getting the job done comes from Lonnie Bowlin’s company, Aerospace Engineering (see “Mighty Atom”).
Become an MIT Technology Review Insider for in-depth analysis and unparalleled perspective.Subscribe today