user: Question: How many fatalities occurred for an Unknown tail number?
Columns: ['Location', 'Aircraft', 'Tail number', 'Aircraft damage', 'Fatalities']
Types: ['text', 'text', 'text', 'text', 'text']
Sample row: ['Quelimane', 'Lockheed L-14', 'CR-AAV', 'W/O', 'Unknown']
SQL:

assistant: SELECT "Fatalities" FROM "Table" WHERE "Tail number" = 'Unknown';