George T. Straza, a flamboyant former jet parts manufacturer convicted last month of defrauding a government contractor by double-dealing in engine components, was sentenced to three years in prison and fined $239,400. Also sentenced by San Diego U.S. District Judge Leland C. Nielsen was Alice Skinner of Lakeside, Straza's former personal secretary at Jet Air Inc. of El Cajon. Skinner, 57, was placed on two years probation and fined $1,000 by Nielsen, who hinted that he believed that Skinner was roped into the conspiracy. Straza, 58, was allowed to remain free on bail pending an appeal of his conviction. Nielsen gave the Rancho Santa Fe businessman two weeks to post a $1-million personal surety bond.