NASA's quiet engine programs.

It is the goal of NASA to provide the technology that will make the aircraft unobtrusive in its environment. The primary work in propulsion source noise reduction centers around the technology to modify existing engines and the technology to design new propulsion systems for CTOL, STOL, and VTOL that operate at significantly lower noise levels than present systems. It is recommended that noise standards should also be established for new engines. Another recommendation is concerned with the incorporation of noise and pollution technology in military aircraft propulsion developments.