Rebelyell

I read a magazine article recently that had information about how airlines were working to keep weight down and how much they saved in a year for each pound or kilo of weight they were able to shed. It was a pretty good amount although I can't remember the figure. Given the way they have started cracking down on overweight luggage it must be a real cost.

If I read the article correctly, it said half the fuel on long-haul flights (I presume trans-Pacific) was used just to carry the gas for the trip, and suggested that if fuels costs continued to rise there might be a return to the days of shorter hops for refueling.

Anyway, just curious if anyone can come up with a ballpark figure of about how much the marginal cost is to transport one pound 1,000 miles, and whether it is a significant amount. Of course, when we're talking about luggage and passengers, we're talking about more than one pound. I realize planes differ and it must be a ballpark figure.

Part two of this question, assuming it is possible to calculate a marginal cost per mile per pound (and the cost actually amonts to something), is would you be willing to fly on an airline that charged a flat fee for each seat and then charged extra for poundage, whether it be luggage or body weight. In other words, instead of pricing a round trip at $300 they might price it at $200 plus fifty cents per pound, or whatever. Needless to say a family with small children flying up to grandma's for the weekend would likely pay less per pasenger than a team of sumo wrestlers with a full load of luggage.

Personally I would like such a system because it would make everyone pay their fair share. Right now, I tend to overpack. If I had to pay for every pound I might try to pack a little lighter, which would be to everyone's benefit. Of course, I might watch my own weight a little more, too.

deubster

I've heard of some puddle jumper flights that weighed customers and luggage to balance the plane, but I've never been on one. I'm guessing the first airline that includes customer weigh-ins as part of its pricing and ticketing will lose all its potential female customers, and will never earn a dime thereafter.

Rebelyell

You may be right, except that most women weight a lot less than men. I don't know if you've ever seen women split a bill at a restaurant, but they get it to the penny (obviously a stereotype, but more often than men). I would think they would love the chance to fly for 10 to 20 percent less.

swag

This article reports that airlines average 49 revenue-passenger-miles per gallon of jet fuel. That's about 20 gallons per 1K miles/pax. Jet juel is about $2.10/gallon recently, so $42/pax/1K miles.

If the average pax + bags weighs 200 lbs, that's 21 cents per pound/1K miles.

Not sure how cargo fits into that equation.

And of course, that's not the marginal cost - the empty plane itself is heavy and that cost is buried here. But it's a ballpark starting point.

LarryJ

Not even close.

$42/passenger in a 137 seat SWA 737, for example, would be $5754 in jet fuel. At your $2.10/gal figure that's 2740 gallons or 18,358 pounds. That's enough fuel to fly a 737 for over 3˝ hours including flying the weight of the airplane, bags, cargo, etc.

Bobster

I may have the answer using this sample chart for a 777-200:
http://www.boeing.com/commercial/air...sec3charts.pdf

The last 20,000 pounds of payload requires an extra 5,000 pounds of fuel to maintain a constant range of 3,300 nautical miles. (In other words, starting from a 100,000 pound payload, we add 20,000 more pounds to get the marginal difference for the 120,000 pound maximum payload. The chart shows that the extra 20,000 pound payload adds 25,000 pounds to the gross weight, therefore an extra 5,000 pounds of fuel was required.)

So, if a passenger has a total weight of 200 pounds, including baggage, that would require 50 pounds of extra fuel. Roughly. Converting to cost will be left as an exercise for the reader.

Bobster

Oh, by the way, my calculation neglected to mention that it takes a little under 100,000 pounds of fuel to fly the plane with no payload. So each passenger is also reponsible for their share of that 100,000 pounds.

Rebelyell

Bobster, you've enabled me to answer my question. If we convert the nautical miles to real miles we get about 3,800 miles. Jet fuel weighs 5.2 pounds per gallon, which I'l calculate at 5 pounds per gallon. So it takes 10 gallons of fuel to transport 200 pounds 3,800 pounds.

To get closer to my original question, It takes 1.3 gallons of fuel to transport 100 pounds 1,000 miles. By my calculation, it takes 1.664 ounces, more or less, to transport 1 pound of weight 1,000 miles. If we calculate the cost of jet fuel at $2.50 per gallon, then the cost to carry one pound 1,000 miles is 4.16 cents, at least on a 777.

At least I think that's the answer. Someone check my math and logic. Thanks Bobster for coming up with the facts.

Bobster

I figure it's 0.25 pounds of fuel to carry 1 extra pound for the full 3300 nautical miles on a 777. Divide that by 6.7 (not 5) to get 0.037 gallons. At $3 per gallon, it would cost 11 cents per pound. So, if you want to penalize a passenger for being 10 pounds overweight, that's about a dollar.

Since the 777 isn't designed for 1000 mile flights, you'd have to lookup the graph for a more reasonable plane like the 737.

correction: Actually, it's OK to use the 777 for a 1000 statue mile flight. The problem is that it's hard read the graph that Boeing provides on their web site for that distance. It looks like a couple thousand pounds of extra fuel for the last 20,000 pounds of payload. Even though the 777 is less efficient at the shorter distance, the cost of the extra fuel required is still less than it would be on the longer flight, or less than a dollar for being 10 pounds overweight.

swag

So a 3.5 hour flight is what, about 1700 miles? Vs. the 1000 I estimated? That's actually kind of close. Biggest source of the discrepency is likely that the numbers I used were per revenue-pax-mile. Not sure what the average number of revenue-pax are per flight, but accounting for empty seats, award tix, deadheaders, and employees, I'll bet that explains most of the gap.

But good to see some better numbers posted.

LarryJ

It's 6.7 pounds per gallon.

70% off is close? It also included the weight of the airplane and cargo, not just the passenger's weight.

tlglenn

This looks like a problem that can be solved using calculus.

LarryJ

It's not that bad...

Roughly 1.75 gallons per mile for a B737NG at about 140,000 pounds total weight. So that's 0.0125 gallons per pound per 1000 miles.

Bobster

For the 737-900 (no winglets) I get 0.0155 gallons per pound per 1,000 statute miles.

(Payload 48,000 pounds, fuel 5,000 pounds extra compared to zero payload.)

Less than a nickel a pound.

sbm12

Strangely a friend of mind sent me an email about this topc recently that I found interesting, if not a bit lacking in all the details. It comes from an AA employee, so that should (theoretically) lend some credibility to it, but judge for yourself...