At what minimum occupancy ratio can airlines operate profitably? Often, airlines are unable to sell all the seats of a flight and some seats go unsold. So, with what occupancy ratio is it usually profitable for an airline to operate?

For example, Recently, a Turkish Airlines A330, flying from Bangkok to Istanbul (12,000 KM) made an emergency landing after a bomb hoax. The interesting thing was that it was carrying only 142 passengers, against its marked capacity of 250 passengers (occupancy ratio of about 0.6). 

And what are the factors which would influence this choice – like probably, it would be cheaper to operate a B787 with 0.6 occupancy ratio compared to a B747.
What are some other factors which influence this?
They can operate with 0 passengers, but will most likely not generate any revenue (unless cargo is carried to generate additional revenue). Revenue and profit on a passenger flight (assuming no paid cargo) will be based upon how many tickets were sold at which price, so the number of passengers required for any given flight to break even will be variable and cannot be answered in a general way.