CREATE TABLE table_659 ("No. in series" FLOAT, "No. in season" FLOAT, "Title" TEXT, "Directed by" TEXT, "Written by" TEXT, "Original air date" TEXT, "U.S. viewers  ( million ) " TEXT)

When did the episode 'Hell bent for leather' originally air?
SELECT "Original air date" FROM table_659 WHERE "Title" = 'Hell Bent for Leather'
SELECT "Original air date" FROM "table_659" WHERE "Title" = 'Hell Bent for Leather'