Question: Who is the callsign that has ICAO of SCO?
SQL: SELECT "CALLSIGN" FROM "2-15520072-1" WHERE "ICAO" = 'SCO';

Question: Who is the commenced operations that has icao of SLK?
SQL: SELECT "COMMENCED OPERATIONS" FROM "2-15520072-1" WHERE "ICAO" = 'SLK';

Question: Who is the call sign that has a commenced operation before 1976?
SQL: SELECT "CALLSIGN" FROM "2-15520072-1" WHERE "COMMENCED OPERATIONS" < 1976.0;