While discussing a different topic, this came up so I just want to see what others think. There is a perception that the two have no correlation and a full flight can lose money and a flight with less than 20 percent of the seats full can make money. I tend to think they are more related.

I don't know the intricacies of revenue system. But I still have this nagging doubt so I put together 2 scenarios for comparison on a long haul domestic flight, interesting numbers came up.

#1 20% full plane (all flying full Y fare very optimistic)
20 ppl x $2800 Full Y = $56000

#2 80% full plane (ppl flying on different classes of fare)
L class 25 ppl x $350 =$8750
Q 25 x $450 =$11250
V 25 x $500 =$12500
H 25 x $700 =$17500
Y 3 x $2800 =$8400
Total $58400

If my numbers are correct, I don't believe a 80% full flight could lose money vs. a 20% full flight. Your thought?