user: Question: Who is the call sign that has a commenced operation before 1976?
Columns: ['AIRLINES', 'IATA', 'ICAO', 'CALLSIGN', 'COMMENCED OPERATIONS']
Types: ['text', 'text', 'text', 'text', 'real']
Sample row: ['Jetstar Asia Airways', '3K', 'JSA', 'JETSTAR ASIA', 2004.0]
SQL:

assistant: SELECT "CALLSIGN" FROM "Table" WHERE "COMMENCED OPERATIONS" < 1976.0;