Although the High Speed Civil Transport of the 21st century may dominate airline service on long overwater routes, the subsonic jetliner will continue to handle most overland travel. The subsonic aircraft market - estimated at $1 trillion over the next two decades - will constitute the bulk of the total market.

U.S. manufacturers hold a 67 percent share of that market, but their share has eroded considerably since 1985 and the principal competitor, the European Airbus consortium, expects to capture half the total market by 2000. It would be a major blow to the U.S. economy should that happen.

The U.S. aviation industry faces other challenges. U.S. airlines estimate that capacity limitations of the National Airspace System cost them $3.5 billion a year in delayed flights. Having experienced heavy financial losses in recent years, the airlines are flying their aircraft longer, a situation that demands new technology to ensure safety over a jetliner's longer life span that is in many cases 30 years. There is further demand for new technology to meet increasingly stringent environmental regulations in the U.S. and abroad.

Therefore, NASA, other government agencies and U.S. plane builders are engaged in an Advanced Subsonic Technology (AST) program that has two strategic thrusts: developing high leverage technologies that will assure the future competitiveness of U.S. civil transports, and finding new ways to enhance the safety, productivity and environmental acceptance of the national air transportation system. AST research involves the whole spectrum of investigational facilities, including computational facilities, laboratories, wind tunnels, propulsion test beds, and flight test. The photo at left exemplifies the wind tunnel testing being accomplished, in this case a wing and a nacelle of the new Boeing 777 twinjet. At right is Langley Research Center's Transport Systems Research Vehicle, a Boeing 757 jetliner modified for flight test of advanced navigation and landing systems, flight controls, weather aids, systems for improving terminal area productivity and other airborne equipment. Among the areas being addressed under the AST program are:

* Aging Aircraft. An area of focus is development of advanced non-destructive evaluation techniques to detect disbonds, fatigue cracks and corrosion, and to enhance aircraft inspection techniques by developing analytical tools for quantitative evaluation of inspection findings and for predicting the residual safe structural life of an aging airplane.

Environmental Assessment. The impact of aviation on the atmosphere is becoming more and more a matter of concern in developed nations and jet liner cruise emission standards are being considered. To assure that the interests of U.S. aviation are fairly represented in international regulatory considerations, NASA is conducting a comprehensive scientific assessment of emission effects on the upper troposphere and the lower stratosphere. The goal is to develop technology, by 2000, that will provide a U.S. capability for assessing changes in atmospheric ozone caused by aircraft emissions.

* Noise Reduction. NASA's aim is to develop technology that will enable an airplane noise reduction of 10 decibels below the mean level of 1992 in order to help achieve compliance with increasingly stringent noise standards.

* Terminal Area Productivity. NASA seeks to develop technology for achieving the instrument weather capacity of the National Airspace System to the point where it is equivalent to clear-weather capacity. One goal is a 12 -15 percent increase in capacity over that of current non-visual operationson a single runway; another is to demonstrate the feasibility of increasing capacity on parallel runways by reducing the spacing between aircraft.

Propulsion. AST work involves development of concepts for reducing ozone-depleting nitrogen oxide emissions; and improving fuel consumption for future commercial aircraft engines.

* Composite Materials. Composites offer potential for reducing aircraft weight, hence cutting costs, but composites have so far been limited to secondary aircraft structures, such as wing leading edges, flaps, ailerons, fairings and access doors. Researchers feel that the technology can be extended to primary structures, which could produce significant cost benefits and competitive advantage. NASA's goal is development and ground test of a full-span composite wing and center section by 2000.

* Integrated Wing Design. This area involves designing wing components in an integrated manner to reduce cost and design time while improving aircraft performance, NASA seeks more efficient high lift devices for low speed takeoffs and approaches with minimal noise impact on the community, together with drag-reducing laminar control of the airflow over the wing.

* Fly-by-Light/Power-by-Wire. Fly-by-light means replacing the current fly-by-wire control systems with lightweight, highly reliable fiber optical systems that eliminate the concerns of electromagnetic interference associated with fly-by-wire. Power-by-wire involves replacing hydraulics with an electrical power actuation system.

* CivilTiltrotor. The shorthaul tiltrotor transport offers promise as a means of transportation to and from city centers and an attendant easing of congestion at outlying hub airports. The AST program addresses technologies that will overcome the "inhibitors" to acceptance of this new types of transport. Target areas include reduction of rotor noise, procedures for steep descents, safe flight with one engine inoperative, and all-weather operations.