CREATE TABLE table_40674 ("AIRLINES" TEXT, "IATA" TEXT, "ICAO" TEXT, "CALLSIGN" TEXT, "COMMENCED OPERATIONS" FLOAT)

Who is the call sign that has a commenced operation before 1976?
SELECT "CALLSIGN" FROM table_40674 WHERE "COMMENCED OPERATIONS" < '1976'
SELECT "CALLSIGN" FROM "table_40674" WHERE "COMMENCED OPERATIONS" < '1976'