In a bowl, beat egg yolks and 1/2 cup sugar until thick and lemon-colored. Stir in the pineapple. Combine cracker crumbs and baking powder; stir into the pineapple mixture. Add pecans and set aside. In a bowl, beat egg whites until foamy. Gradually beat in remaining sugar until soft peaks form. Fold into the pineapple mixture. Pour into an ungreased 9-in. springform pan. Bake at 350° for 30 minutes or until top springs back when lightly touched. Cool on a wire rack. (do not remove sides of pan.)
Dissolve gelatin in boiling water. Stir in cold water; refrigerate until mixture begins to thicken, about 40 minutes. Stir in bananas; pour over cooled cake layer. Refrigerate until firm, about 2 hours.
In a bowl, beat cream and sugar until soft peaks form; pipe or spoon over gelatin layer. Just before serving, run a knife around the edge of pan to loosen; remove sides of pan. Garnish with cherries if desired.