CREATE TABLE table_21627 ("Series #" FLOAT, "Season #" FLOAT, "Title" TEXT, "Directed by" TEXT, "Written by" TEXT, "Original air date" TEXT)

What is the original air date of the episode directed by Terrence Nightingall?
SELECT "Original air date" FROM table_21627 WHERE "Directed by" = 'Terrence Nightingall'
SELECT "Original air date" FROM "table_21627" WHERE "Directed by" = 'Terrence Nightingall'