user: Question: What date did the episode air that had N/A for it's bbc three weekly ranking?
Columns: ['Episode no.', 'Airdate', 'Viewers', 'BBC Three weekly ranking', 'Cable rank']
Types: ['real', 'text', 'real', 'text', 'text']
Sample row: [1.0, '25 March 2010', 862000.0, '3', '13']
SQL:

assistant: SELECT "Airdate" FROM "Table" WHERE "BBC Three weekly ranking" = 'N/A';