* Frank Mann, 84, an engineer and aviator whose friendship with Howard R. Hughes from the time they were both teen-agers led to a starring role in the "Amos 'n' Andy" radio show and participation in the "Spruce Goose" seaplane project, died Sunday in Houston. With his friend's assistance, Mr. Mann, who was black, worked in a previously segregated shop, went to college and earned a mechanical engineering degree. He flew reconnaissance missions for Ethiopia in 1935 after Italy's invasion of that country. He later performed as a stunt pilot, wing walker and parachutist for a flying circus in Europe. As a Hughes employee in California, he assisted in movie productions and for a time played both principal roles in the "Amos 'N' Andy" radio show. Later, Mr. Mann worked on development of the first communications satellite for commercial use. He was to be cremated and his ashes were to be scattered over a runway at the Los Angeles International Airport.