CREATE TABLE table_73978 ("No. in series" FLOAT, "No. in season" FLOAT, "Title" TEXT, "Directed by" TEXT, "Written by" TEXT, "Original air date" TEXT, "U.S. viewers  ( millions ) " TEXT)

What was the original air date for the episode with 13.92 million us viewers?
SELECT "Original air date" FROM table_73978 WHERE "U.S. viewers (millions)" = '13.92'
SELECT "Original air date" FROM "table_73978" WHERE "U.S. viewers (millions)" = '13.92'