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_40674 ( "AIRLINES" text, "IATA" text, "ICAO" text, "CALLSIGN" text, "COMMENCED OPERATIONS" real )

### Question ###
Who is the call sign that has a commenced operation before 1976?

### Accurate SQL ###

SELECT "CALLSIGN" FROM table_40674 WHERE "COMMENCED OPERATIONS" < '1976'