Below is the list of tables from the database along with their columns and datatype. Need to generate an accurate SQL query for the question.
Only use the columns present in the respective table. Only use the columns which are required to generate the SQL query. Only use table joins if required and not otherwise.

### Tables ###
TABLE: CREATE TABLE table_24399615_8 (airdate VARCHAR, cable_rank VARCHAR, viewers VARCHAR)

### Question ###
When 656000 is the amount of viewers and n/a is the cable rank what is the airdate?

### Accurate SQL ###

SELECT airdate FROM table_24399615_8 WHERE cable_rank = "N/A" AND viewers = 656000