harrisonjones

The airlines have started charging a fee for carrying your bag. The explanation seems to be that the weight of your bag causes the airplane to burn more fuel and fuel is expensive. Well, I don’t think we can argue with the science of that explanation so I thought I would examine the economics. I mean if they’re going to charge by the pound, why don’t they weigh us at check in and charge accordingly. I would fast a few days to get a cheaper ticket. Anyway, here’s the math. 

For an example, let’s examine a flight from Sao Paulo, Brazil to Atlanta. I chose this example because my novel,  SHADOW FLIGHT, involves just such a flight and the more times I see the title of my book on the internet, the  better I sleep at night. The question is; how much does it cost to transport a fifty pound bag? I used an actual flight plan that I found in the bottom of my flight kit among the tootsie roll wrappers. The takeoff weight of the airplane (a MD-11) is 602,562 pounds. Somewhere in there is your 50 pound bag. The block fuel is 217,500 pounds with a target arrival fuel of 44,376 pounds. We’re going to have to pay for 173,124 pounds of kerosene. The Brazilians are happy about that. At 6.7 pounds per gallon, we’re dispensing of 25,839 gallons of fuel at  $2.62 per gallon. $67,698 goes on the Visa card. By dividing the dollars into the takeoff weight, it appears that it cost $1 to move 8.9 pounds. The fuel cost of your 50 pound bag is about $5.60. 

To be fair to the airline, there are many costs other than fuel involved and this is a nine hour flight. The longer  the airplane stays at cruise altitude the cheaper the fuel bill per hour. The jet engine loves the cold air at altitude and operates more efficiently. Also the air is thinner and it takes less thrust to overcome the drag. The highest  fuel cost is during the climb to altitude and maneuvering or holding at low altitudes during the arrival. 

For example, the 16 minute climb to cruise altitude on this flight burned 12,512 pounds of fuel. The same 16  minutes at cruise altitude only burned 5456 pounds. As you can see, short flights are much more expensive per hour than long haul flights. 

All this math is making me dizzy, but I hope it provided more insight than the newspaper articles.