Highway in the Sky

Just imagine your car could fly.

It'll be a long, long time-maybe Infiniti-before your Thunderbird could Venture down the interstate and sprout wings at the first sight of a traffic jam. But don't Saab. Your Expeditions could become smoother in the not-too-distant future, because the government is paving a highway in the sky.

A public-private partnership that includes NASA, the Federal Aviation Administration and the nonprofit National Consortium for Aviation Mobility spent $150 million during the past five years developing technology to enable the nation's 5,400 rural and suburban airports to accommodate more planes. Nine out of 10 Americans live within 30 miles of one of these small, underused facilities.

When you ride on a plane between bigger, busier airports, how fast do you go? If you're a typical airline passenger, according to one federal estimate, your door-to-door speed is just 50 mph to 80 mph on trips shorter than 500 miles. If time is your only concern, then you might as well skip the security hassles and drive. Sometime in the next year, the command of the wheel and the comfort of the clouds will merge in a new breed of airplane, the microjet.

These tiny jets-with two engines, six seats and the interior volume of a sport utility vehicle-will begin transporting travelers across the country, to and from small airports without scheduled service. Passage in an air taxi will cost about as much as a first-class ticket on a commercial airliner initially. But the price is likely to drop substantially in the next couple of decades as personalized point-to-point air travel rises in popularity.

NASA, which helped develop the microjet, envisions this mode of transportation becoming so affordable and convenient that many families would want to substitute a microjet at the local airstrip for an extra car in the driveway. FAA sees these facilities as a route to easing gridlock in the air. The aviation agency has a goal of boosting national airspace capacity by 300 percent in 20 years, and it figures that shifting demand to less congested parts of the transportation system will help.

But general aviation airports often can't afford the control towers, radar and navigation systems necessary to operate around the clock in all kinds of weather. So the space agency removed the need. Its aeronautical scientists, aided by researchers from academia and industry as well as local and state aviation authorities, developed the Small Aircraft Transportation System. It's an onboard guidance suite based on the Global Positioning System, and it can do the work of expensive ground equipment.

If SATS technology catches on, it could be installed in the cockpit of just about any fixed-wing general aviation aircraft to enhance the pilot's situational awareness in the rush of air traffic and enable a safe landing at a minimally equipped airport. For a demonstration coordinated by the consortium in June, a team based at NASA's Langley Research Center in Hampton, Va., tricked out six small planes with enhanced cockpit displays, advanced communications, satellite navigation tools, and military infrared and low-light camera technology. The airplanes flew and landed safely at tiny Danville Regional Airport in southern Virginia, about 80 miles from Raleigh, N.C.

The instrument package let the pilots peer through fog, see the positions of the airplanes around them, and communicate directly from plane to plane. An airport management module-the essential piece of hardware on the ground-received and relayed radio pulses with each plane's identifying information, took landing requests from the planes, and assigned them numbers in a landing queue.

Planes approaching airports such as Danville when visibility is poor usually must request permission to land from a distant air traffic control center. To ensure safety, the faraway center limits operations to as few as four takeoffs or landings per hour. In the demonstration, SATS handled six aircraft in 40 minutes at Danville and is said to be able to manage up to 15 per hour even in bad weather.

The demonstration capped a five-year development plan. Whether SATS ultimately takes off is up to the federal organization that is designing and implementing FAA's Next Generation Air Transportation System. The multiagency Joint Planning and Development Office must determine how technology for self-controlled runway approaches fits into the grand flight plan for 2025.

The SATS premise has its challenges. The demonstration involved six planes, not thousands. Air routes won't necessarily follow paved highways, but could go over residential neighborhoods at low altitudes. Industry observers ask: Who's going to maintain all these airplanes? Another debate is whether the growth of on-demand air travel will cripple the national airspace system, rather than increase capacity.

The National Academies' National Research Council is among the skeptics. In the 2002 report "Future Flight: A Review of the Small Aircraft Transportation System Concept," a committee of the Transportation Research Board expressed doubt that SATS aircraft could be made affordable for use by the general public. It identified infrastructure limitations and environmental concerns as obstacles to SATS deployment at many small airports.

The report also predicted "undesirable outcomes" in light of elevated security concerns since the Sept. 11 terrorist attacks. It questioned how airfields could be safeguarded to prevent aircraft misuse and whether SATS is compatible with the need for centralized authority during an emergency such as a threat from multiple aircraft. The research board acknowledged the predictable course adjustments possible with highway-in-the-sky systems could make flight operations more secure. But at the same time, the board noted, technology that makes it easier to fly could allow more people to operate aircraft for illegal or illegitimate purposes.

NASA is betting on a future in which such challenges have been overcome. In July, the space agency teamed with the nonprofit Comparative Aircraft Flight Efficiency Foundation to offer annual prizes totaling $250,000 for technology innovations to minimize noise and maximize handling qualities of general aviation or sport aircraft. The contest is the fifth in NASA's Centennial Challenge series, and it's designed to stimulate development of personal air vehicles-flying cars. More than half the purse will go to the team whose vehicle demonstrates the best overall flight performance, measured in a calculated score that includes door-to-door trip velocity, energy consumption and passenger carrying capability.