Noise and vibration in aircraft cabins not only disturb passengers, it adds extra wear and tear on the plane's structure and can interfere with military surveillance missions. A new system developed by Hood Technology of Hood River, Ore. through the Navy's Small Business Innovation Research program controls interior noise and vibration, especially in propeller-induced sound within turbo-prop aircraft. The Active Tuned Mass Absorber (ATMA) does for airplanes what shock absorbers do for automobiles. The ATMA reduces the source of the noise instead of trying to cancel it with more noise or vibration as other active systems do. The sophisticated yet simple system is composed of a computerized control unit and cylindrical absorbers made of adaptive damping rubber. The absorbers tune themselves to disturbance tones using a continuous feedback loop. The absorbers may be installed in the plane's interior or exterior, depending on the type of aircraft. The novel approach employs structural control rather than acoustic or structural-acoustic control. More than 200 units of the ATMA have been installed on DC-9 and MD-80 aircraft. ATMA reduces the interior noise in the rear of a DC-9 aircraft by 90 percent. Passengers can now enjoy a pleasant flight without having to shout to talk to the flight attendant. Today, more than 100 Northwest Airlines and Midwest Express DC-9 and MD-80 aircraft are equipped with ATMA. Flight demonstrations conducted on Navy E-2C aircraft and Air Force/Marine Corp MH-53 helicopters confirm the acoustic performance demonstrated in the DC-9.