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Is there any airline which are able to get the complete 20% fuel efficiency on their 787 with respect to 767 it is going to replace, as told by Boeing.

I have read that one of the early customer like Air India are not able to get even 15% of fuel efficiency on their Dreamliners.

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    $\begingroup$ What does "20% efficiency" even mean for an jet engine? Efficiency is defined as useful energy out divided by total energy in, but jet engines are always rated by thrust. You can get some kind of meaningful "useful energy out" if you multiply that by the forward speed but that would be less than conventional, and anyway airlines would want to exceed the specified velocity for peak efficiency in order to better amortize their capital and fixed costs. Do you mean 20% reduction with respect to a previous benchmark as the existing answer has assumed? $\endgroup$
    – Level River St
    Jun 23, 2015 at 13:30
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    $\begingroup$ 20% better than what? A 767? A 707? An A350? A DC-3? The Space Shuttle? $\endgroup$
    – reirab
    Jun 23, 2015 at 15:55
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    $\begingroup$ Yeah, its comparing with 767 and taken this as a benchmark. $\endgroup$
    – NitinG
    Jun 24, 2015 at 7:17
  • $\begingroup$ It depends on the role they are using the aircraft for. Short haul it will use more fuel on more climbs out of airports etc, long haul it will be sat at 40,000ft cruiseing along. Quite like a car, it takes more fuel to get a car to 70mph (like taking off) than it does to keep it at 70mph. Using them on short haul will use more fuel. thats why the likes of AI cannot get them to work as they want - plus AI's maintenance is a little concerning for the lay person like myself, for instance VT-ANI was "undergoing short maintenance" (like a A check) for around 9-10 months, usual time for an A-check i $\endgroup$
    – David Cummings
    Dec 13, 2016 at 8:16
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    $\begingroup$ @LevelRiverSt, where does the question mention a jet engine? It does not. It asks for ‘efficiency’ of the aircraft. Saying ‘consumption’ would be formally more correct, but fuel efficiency is common term. $\endgroup$
    – Jan Hudec
    Aug 12, 2017 at 10:04

4 Answers 4

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You have not defined your benchmark/reference value, but a three-year-old article suggests this was possible depending on definition even at a very early stage for some airlines:

ANA earlier this month was the first to reveal that its aircraft were producing around 21% lower fuel burn on international flights compared to the 767-300ER that the 787 is designed to replace.

They also say however:

After its first six months of service, ANA says the 787 efficiency levels are slightly up on the 20% savings originally expected at the beginning of the program. On domestic routes, the saving is 15-20%, which meets expectations, say ANA officials.

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    $\begingroup$ The article isn't clear on how they measure efficiency -- are they comparing fuel burn of a 767-300ER to the 787 on the same route, or are they looking at per-passenger fuel costs? Wikipedia says the 767-300ER has a typical seating capacity of 290 passengers (up to 350 in a single-class configuration), while the 787-8 seats 242 in a typical configuration (up to 375 for a single-class). So it would be interesting to know if the efficiency gains takes into account differing passenger counts between the two planes. $\endgroup$
    – Johnny
    Jun 23, 2015 at 18:14
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    $\begingroup$ GIven that this is a marketing term, it's extremely likely that the measurement here is actually "fuel burn per seat-mile". This is the metric that airlines generally use to measure and assess fuel efficiency for the airplane. It can be a little deceptive, because you could increase "efficiency" 5% just by adding 5% more seats... but that's how these things are normally discussed. $\endgroup$
    – ljwobker
    Jun 24, 2015 at 17:42
  • $\begingroup$ Wouldn't the extra weight of those seats (and passengers...) cause an increase in fuel consumption, though? So by adding 5% more seats (assuming all other relevant regulations remain met) you might increase the number of seat-miles by a little less than 5%; say, perhaps, 3%. $\endgroup$
    – user
    Aug 14, 2017 at 12:40
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Wikipedia's B787 article states that:

According to data from launch customer All Nippon Airways, the 787 surpassed the promised 20% fuel burn reduction compared to that of the Boeing 767.

This newer (8 months old) article states that:

Air Canada and Japan Airlines are on the way to achieve it.

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As the other answers say, ANA is happy with the 787 surpassing the 20% fuel savings. But that does not mean for any given trip a 787-8 burns 20% less fuel than a 767-300ER. Which makes your point about Air India valid, here's why:

It's not a fair comparison. The ANA 767-300ER on transpacific routes is not in its natural habitat, i.e., it can fly the mission, but it can't carry a full passenger load alongside the lucrative freight.

1. Engines

An academic source mentions the SFC (in cruise) of the GEnx-1B64 being 1.52537x10-5 kg/Ns. Or 0.53852 pounds of fuel per pound-force thrust per hour. Compared to 0.576 for the CF6-80C2B2 on the 767-300ER. In other words, the new engines are 7% more efficient.

Note: The thrust of both engines is quite close at sea-level (3.7% more for the 787-8).

2. Wings

enter image description here
(Own work via boeing.com) Overlayed scaled drawings.

The 787 is marketed as 50% composites, which is lighter. So let's compare the weight to a plane of roughly the same dimensions and passenger capacity: the 767-400ER (not the smaller -300ER).

The Operating Empty Weights are 120 and 104 tonnes. The 787-8 is 16 tonnes heavier. (Strange, right?)

Two things stand out from the drawing above:

  1. The 787 is wider and a bit shorter, which allows wider seats* but neutralizes the composites advantage.

  2. Since the construction materials are lighter, the wings can be built bigger for the same weight. The increased span improves the lift-to-drag ratio, which permits higher speed for the same thrust, and/or the ability to carry heavier fuel loads for increased range.

* Not all airlines will install them of course, but Japan Airlines does for example.

3. Speed

The extra efficiency for the 787-8 comes not only from the new engines, but by also being able to fly faster. If you spend less time in the air, the 7% fuel efficiency is increased further.

For the GEnx, GE advertises on their website:

Up to 15% improved fuel efficiency compared to GE’s CF6 engine.

I ran some numbers based on a hypothetical 200-passenger flight to get ballpark figures. The first row is the new engine, and the following rows are the new engine on the new plane.

Scenario          Pax    Seat mileage

New engine         0     - 7%
+9.5% speed        0     -15%
+9.5% speed       +13    -20%
+6.3% speed       +19    -20%

The +9.5% speed example is going from Mach 0.79 to 0.865, this achieves the advertised GE value.

If Air India is flying shorter or high-density routes, then the full 20% won't be realized. (Air India are very much aware of this, each airline is sold the right projections based on their operations.)

From Wikipedia for the transatlantic routes we have a fair [and well-sourced] apples to apples comparison (I added the rightmost column).

Model            Pax      Distance      Fuel/Seat      Per seat saving
                                        (L/100 km)

787-8            291      6,300 km      2.26           7   %
767-400ER        304      6,047 km      2.43           5.08%
767-300ER        269      5,600 km      2.56           -

Note that the -300ER burns more fuel per passenger while carrying fewer passengers a shorter distance at a slower speed compared to the 787.

To adapt the -300ER for the transpacific, the plane will not be fully loaded, further increasing the fuel per passenger. This allows ANA better efficiency figures when they compare it to the Dreamliner.

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A Real-World example:

On a typical 3,551 NM airways distance flight a 365,000 lbs 767-300ER will take 08:40 and 92,300 lbs of fuel to get there with 216 pax and baggage (no cargo). The flight took longer due to 51 kts of head wind that turned the 3,551 NM into a 3,973 NM air miles (ESAD) flight.

A 424,000 lbs 787-8 will do the same mission in 07:56 and use 86,500 lbs of fuel while transporting 237 pax and baggage (no cargo). And because it flies faster, it spends less time in the 51 kts head wind and only covers 3,875 air miles (ESAD).

The 767-300ER burned 10,600 lbs per flight hour, whereas the 787-8 burned 10,900 lbs per flight hour. More! Except it does so covering more distance as it flies 6% faster.

With (3,973 x 216) seat-miles, the 767-300ER burned 0.1068 lb/seat-mile. The 787-8 burned 0.0942 lb/seat-mile based on (3,875 x 237) seat-miles. The 787-8 is thus 11.8% more efficient per seat-mile.

When dropping the pax load of the 787-8 to the same 216 as in the 767-300ER, we will get a tube-for-tube comparison; 21 pax weigh 4,851 lbs and lowering the payload on the 787-8 by 4,851 on an 8-hour flight will lower trip burn by approx. 1,160 lbs. The burn per seat-mile now changed to 0.1019 and this is only 4.6% more efficient than the 767-300ER.

So... marketing hype. The 20% efficiency gain was based on fuel burn per seat-mile, not tube-for-tube numbers.

In this example it would have taken 20 more pax in the 787-8 to confirm the 20% claim. In other words, have the 787-8 fly with (237+20) 257 pax. The higher fuel burn of 87,700 lbs (due to 20 more pax on board) would be offset by the huge increase in seat-miles and in that way reach the marketed 20% difference in efficiency.

Hope this helps.

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  • $\begingroup$ +1, but the answer would be even better if you revealed the sources for your numbers. $\endgroup$
    – Peter Kämpf
    Jun 10, 2019 at 17:33
  • $\begingroup$ Lido real-world flight plans, ran by myself. $\endgroup$
    – Sander de Moor
    Jun 11, 2019 at 18:05

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