[size=16][font=Arial]George B. Litchford Sr., a prolific aviation inventor who had a vital role in the development of the collision warning system now used on every airliner in the United States, died on Feb. 28 in Albany. He was 89 and had lived most of his life in Northport, N.Y.
His death was confirmed by his son, George B. Litchford Jr.
Mr. Litchford began working in navigation and surveillance technologies for airplanes in 1941 at Sperry Gyroscope Research Labs and was still at it 50 years later. One of his insights was that hardware already on planes that help controllers on the ground keep track of them could also be used in an anticollision system.
The equipment is called a transponder. A rotating radar system operated by the Federal Aviation Administration sends out electronic queries that planes answer with their transponders, robot radios that give the plane
