CREATE TABLE table_26814 ("Episode no." FLOAT, "Airdate" TEXT, "Viewers" FLOAT, "BBC Three weekly ranking" TEXT, "Cable rank" TEXT)

What date did the episode air that had n/a for it's bbc three weekly ranking?
SELECT "Airdate" FROM table_26814 WHERE "BBC Three weekly ranking" = 'N/A'
SELECT "Airdate" FROM "table_26814" WHERE "BBC Three weekly ranking" = 'N/A'