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A recent Washington Post article, titled "Five myths about air travel" noted:

The difficulty is that economies of scale don’t always work for airlines, because planes generally don’t increase in per-passenger efficiency as they grow larger. In fact, many of the most efficient planes of today are the smallest ones. At a transatlantic distance, a 525-seat Airbus A380 has an efficiency of 74 miles per gallon (mpg) per passenger, while the brand-new 168-seat Boeing 737 MAX 8 reaches 110 mpg per passenger.

This seems counter-intuitive. All other things being equal (and transatlantic distances would equalize many of them) -- shouldn't the larger plane should be more efficient?

This whole article notes the "myths about air travel" and I have to admit that I'd always believed that larger planes were more efficient per passenger mile.

Perhaps there is something unique to the the A380 and 737-Max 8 that makes the comparison incorrect? Is it related to aircraft utilization rate or percentage of seats filled -- although these wouldn't be a factor in the mpg per passenger metric?

Note: I am not interested in crew or ground staffing efficiencies realized by a mega plane. Just fuel.

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    $\begingroup$ Shouldn't the unit be passenger miles per gallon, rather than miles per gallon per passenger? If they can't get units right, that makes me dubious about the other claims. $\endgroup$ – Thomas Jun 24 '17 at 3:54
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    $\begingroup$ Another difference is 12 years of innovation (between the first flight of the A380 and the 737 MAX 8) during which much of that time oil was above $100/barrel and low fuel usage was a primary design consideration. A lot of engineering effort went into reducing fuel consumption for the 737 MAX and the A320Neo. The A380's fuel consumption isn't that out of line with similar aircraft of the same vintage either. $\endgroup$ – Zach Lipton Jun 24 '17 at 7:36
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    $\begingroup$ Smaller aircraft need more crew members (per passenger), more ground crew, probably more maintenance. They increase traffic load, ATC load and delays which is money too. I don't know about the impact of this, but it may be taken into account for a fair comparison. $\endgroup$ – mins Jun 24 '17 at 16:13
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    $\begingroup$ @Sanchises Technically, aren't "miles per gallon per passenger" what you would get if you took a number of miles per gallon and divided it by a number of passengers? If your vehicle gets 10 miles per gallon and has 10 passengers, that's 1 mile per gallon per passenger (a useless measurement) but 100 passenger miles per gallon. All that said, the term "miles per gallon per passenger" did sound right to me at first glance. $\endgroup$ – Timber Swett Jun 24 '17 at 18:18
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    $\begingroup$ @RoboKaren It's a bit tough to find 737's on transatlantic flights. There are only a handful on unusual routes and they usually have to limit the number of passengers to get the necessary range. Until recently they just haven't been capable of the range. Although there are numerous other considerations, for fuel efficiency airlines will generally use the smallest plane capable of the flight range. They don't make bigger planes for the extra seats, it's for the extra range. $\endgroup$ – TomMcW Jun 24 '17 at 21:40
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The comparison is seriously flawed. While over the entire duration of the flight the larger aircraft is more efficient per passenger/mile, this is not the case for the flight phases that cause the bulk of the fuel consumption for smaller airliners but only a fraction for larger airliners: takeoff/climb and descent/landing.

A 747 or A380 flying a one hour leg, which is typical for many smaller airliners, would use more fuel per passenger over that leg than does say a 737 or A320, despite being more fuel efficient at cruise altitude (if it can even reach its optimal cruise altitude over that distance).

It is also far less flexible, and requires a higher passenger density than does the smaller airliner, a passenger density that's simply not there on most routes unless you greatly reduce the frequency of flights (in which case you'd best hope all your competitors do the same as passengers are less likely to be happy to wait for your one flight a day at noon when they can get to their destination at 8AM taking another airline's flight).

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  • $\begingroup$ The question specifies transatlantic flights, which are usually four or more hours in duration. $\endgroup$ – RoboKaren Jun 26 '17 at 19:05
  • $\begingroup$ @RoboKaren It doesn't matter much. Not over those distances. And the economic argument still stands. There's a reason airlines go with smaller aircraft and it's because there's no point flying an A380 on a route that only generates enough traffic for a 787, it'd fly with half its seats empty, making it far less efficient. $\endgroup$ – jwenting Jun 27 '17 at 5:55
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update I could read the article just now. It does not consider how many passengers need to be transported. For one A380 you need three B737MAX to fly transatlantic, with 6 pilots etc etc. What they are doing is comparing aircraft per aircraft, and yes a huge plane like the A380 needs a lot more thrust and needs to burn more fuel. But they should be comparing one A380 with three 737s if considering moving 560 people to the other side of the pond.

Range is a variable here as well. How to compare air travel economy for ranges that the A380 are designed for, let's say Paris - San Fransisco. Do the 3 737s make a fuel stop in New York?

The bit on numbers of engines of comparable types is still valid, but mostly for aircraft of comparable size:

The best practical case study is the one performed by Airbus: the same aircraft, powered by either two engines (A330) or four engines (A340). The A330 is still relevant and being updated with NEO engines, the A340 is out of production - not because it was a bad aircraft but because the restrictions on ETOPS have been relaxed. Number of engines is a huge factor, fewer engines means higher efficiency. Each additional engine adds drag from the engine pods, one engine weighs less than two half size engines etc.

When the A380 was designed there was talk of a stretched version, the A380-900. A stretch is easy if the only thing required is to plug in an extra bit of fuselage, but gets very hard if a complete re-design of the wing needs to be considered. It looks like the current A380-800 has the larger wing of the -900 already, in other words: that wing design was optimised for the higher gross weight of the -900. That would be a very economical aircraft - if a big enough market could be found for it.

The B-777 is currently the largest passenger jet with 2 engines. The air travel myth article should consider total traffic volume, and compare the cost per passenger based on that. Economy of the A380 is actually pretty good, but sales of the aircraft seem to be hampered by lack of high traffic volume routes.

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    $\begingroup$ It's still all about range. The A340 was discontinued because of reduced demand for longer range flights. After a certain distance the A340 made up for the extra weight and outperformed the A330. $\endgroup$ – TomMcW Jun 24 '17 at 22:58
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    $\begingroup$ Air Asia could not make the Kl -Lomdon flight work with A340s due to fuel economy, they were holding out for A350 to re-open routes to Europe. $\endgroup$ – Koyovis Jun 25 '17 at 1:14
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    $\begingroup$ The A340 was designed to counteract the very restrictive ETOPS rules in force at the time, which prevented aircraft with two engines from flying many overwater routes that they could otherwise fly (based solely on their range). Fortunately (or unfortunately for the A340) ETOPS extensions (allowing twinjets to fly longer distances away from airports) were approved faster than anticipated, negating the A340's advantage over twinjets. $\endgroup$ – Lightsider Jun 26 '17 at 6:36
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    $\begingroup$ Yes indeed, it made sense at the time. $\endgroup$ – Koyovis Jun 26 '17 at 6:36
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    $\begingroup$ Which is also a prime reason for the untimely (or timely if you're an aircraft mechanic) demise of the MD-11. It was given 3 engines to not need ETOPS classification. $\endgroup$ – jwenting Jun 27 '17 at 5:58

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