 There was no way to composite Spencer Tracy (qv)s image into the  scenes where Van Johnson (I) (qv) is flying, so he actually had to  be standing behind Johnson and, later, Irene Dunne (qv) for the  filming of these scenes. The same approach was used for  _Ghost and Mrs. Muir, The (1947)_ (qv) (techniques for superimposing  one image onto another were not invented until much later).