You make a point, and I certainly don't have the numbers to prove either way. One thing to consider, though, is that the F/C seats that are being removed probably weigh more per row than the coach seats they're adding. So the seats added wouldn't increase weight as much as they would if they were pure additions with no reductions in the F/C cabin.

Just pulling numbers out of the air, say the weight increase is 200 lb. On the narrowbodies, a rough rule of thumb is that fuel burn per hour increases by 5% of the added weight - 10 lb, or about 1.5 gallons, or about $3.

If the average coach fare is $100 (another number pulled out of the air), selling one additional coach seat per 33 hours of flying time (not gate-to-gate time) is breakeven. Given our "average stage length" of about 900 miles, that 33 hours equals about 13 segments.

So using these made-up numbers, selling one additional seat per 13 segments could be break-even.

Jim