Bethpage, N.Y.-based Grumman Corp. reported net income for the third quarter of 1986 increased 91% over the comparable period last year. Third-quarter revenue also was up. Sales increased $304 million in the 1986 period, of which $154 million was attributable to the F-14D and A-6F development programs being performed under no-profit contracts with the Navy. Other increases were in the electronics-systems and information and other service segments. Although the aerospace segment profit declined, sales in non-aerospace segments increased 55%.