Pan American Airways  Sikorsky S-43-B  NC16927     (c/n  4316)


                                                       The S-43B was a twin-tailed version of the S-43.  The method of allocating ATC (Approved
                                                       Type Certificate) numbers by the Dept of Commerce in the 1920s and 30s appears to have been
                                                       quite capricious.  Some machines had almost indiscernible changes made and were given a brand
                                                       new number.  Others had fairly drastic changes (I mean, from a single fin and rudder to twin tails
                                                       does not, to me, appear to be an insignificant or minor design change), but nevertheless retained
                                                       the same ATC number as the original.  Both Sikorsky S-43s were ATC # 593.   Pan Am used
                                                       them interchangeably.