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BG777300ER
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Fuel Burn Of Quad Vs Twin

Fri Apr 01, 2016 3:04 pm

Hello
Does anyone have quick statistics on what the fuel consumption would be for a fully loaded 748 doing SFO-SIN vs the following:
-A350-1000
-787-1000
-777-300ER
-779 (if any fuel consumption projections are available)

My end goal here is: I would like to get an idea of how much more an airline would have to charge on tickets on a 748 flight, to cut even the extra fuel costs it would incur vs flying those passengers on this route in a big twin engine airplane.

I know in theory this route is pushing the limits on range, but lets just assume all these planes can make it.

Thanks

[Edited 2016-04-01 08:08:28]
 
flipdewaf
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RE: Fuel Burn Of Quad Vs Twin

Fri Apr 01, 2016 3:12 pm

I'm sure someone will be able to provide you with real life fuel flows seen from the cockpit but the number of engines has very little to do with the fuel burn of an aircraft. Being a quad has benefits to fuel burn in some areas and drawbacks in others but in the overall fuel burn figures there will be other much more influential things.

And remember that correlation does not equal causation.

Fred
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BG777300ER
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RE: Fuel Burn Of Quad Vs Twin

Fri Apr 01, 2016 3:18 pm

Interesting point. Can you elaborate on some of these? I am looking to understand why there is such a huge movement of airlines to go from 4 to 2 engines. The answer I keep hearing is "fuel efficiency $$$ savings". I would like to understand what that magical number there is that is being discussed at airline boardrooms and convincing CEOs to stay away from buying planes like the 748.

[Edited 2016-04-01 08:18:53]
 
roseflyer
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RE: Fuel Burn Of Quad Vs Twin

Fri Apr 01, 2016 3:29 pm

Other than possibly the 777-9, I don't think any of the airplanes you ask about could fly SFO-SIN nonstop with a full passenger load. A 777-300ER doesn't have enough to fly SFO-SIN against the winds. The 777-300ER can fly over 8,000 miles on a polar route, but probably would have to limit the number of passengers on a transpacific route.

When looking at the numbers, the 747-8 burns similar amounts of fuel per seat for a similar configuration as a 777-300ER. The 747-8 may be a little less. It uses more modern engines and has higher capacity to spread out the fuel costs. There's no easy direct comparison, but people over at Air China probably can compare fuel burn.

Guessing fuel burn for airplanes that haven't even been built yet is not easy. You won't find a good answer on A.net.
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BG777300ER
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RE: Fuel Burn Of Quad Vs Twin

Fri Apr 01, 2016 3:43 pm

Thanks for the input, I just wanted to pick a theoretically long route.

So to sum it up, what is causing airlines to ditch quads over twins? I realize environment is one, but no airline would ever ditch something just to help the environment.
 
Flighty
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RE: Fuel Burn Of Quad Vs Twin

Fri Apr 01, 2016 3:55 pm

Twins have less maintenance. Around "15%" less fuel burn (using Airbus A330/A340 as a quasi example). Which is a massive number. Fewer engines to purchase.

In the other direction, a quad needs less total thrust (notwithstanding that it probably weighs more). But instead of 200% of required thrust, it only requires 133% required thrust to facilitate engine-out. So quad allows you 1/3 less installed thrust than twin, 33%, very large number there.

That about covers my simple minded answer.
 
LAXtoATL
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RE: Fuel Burn Of Quad Vs Twin

Fri Apr 01, 2016 4:33 pm

Quoting BG777300ER (Reply 4):
So to sum it up, what is causing airlines to ditch quads over twins? I realize environment is one, but no airline would ever ditch something just to help the environment.

I really am not qualified to answer your questions about fuel burn. Like you, I assumed that twins were more fuel efficient than quads - but I guess if you consider that quads use lower thrust engines than quads (assuming same technology) I can see that there wouldn't be much difference on a CASM basis.
Anyway as we both agree airlines aren't making business decisions based on the environment, one reason airlines would prefer twins over quads would be maintenance costs. Quads would require twice as much time and money to maintain.
 
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RE: Fuel Burn Of Quad Vs Twin

Sat Apr 02, 2016 2:16 am

Some random thoughts which may or may not be correct.

- Have fewer engines always been more efficient assuming there are powerful enough engines for the size? It seems that more or less as soon as engines become powerful enough to power a certain aircraft size with two engines only, no designs with more than two engines are considered ever again. Examples: In light pistons, if you can get away with one engine instead of two for the same payload, you'll be using less fuel. The only reason there are still so many light twins around is pilot training and simple inertia (light pistons have long service lives). Scaling up, in the 60s you could build a 737 sized aircraft with two engines. After that no one seemed to thing "let's use more engines for this size".

- As fans have become larger and larger, the parasite drag from the engines, cowlings and pylons has increased. The drag impact of more engines is thus larger now than it was in the age of turbojets or low-bypass fans. But even in the days of yore, more engines meant more drag and more weight. Furthermore, turbofans tend to become more efficient with larger size.

- Comparing a 350 with a 340 is a bit unfair. The 350 has the advantage of 25 years of advancements in technology covering everything from aerodynamics to propulsion to materials. The "real" comparison would be a four-engined 350 with a two-engined 350.
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Matt6461
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RE: Fuel Burn Of Quad Vs Twin

Sat Apr 02, 2016 3:24 am

This was discussed quite well in Leeham (Björn Fehrm) On Quads Vs Twins (by anfromme Dec 11 2015 in Civil Aviation)
 
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zeke
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RE: Fuel Burn Of Quad Vs Twin

Sat Apr 02, 2016 4:13 am

Quoting BG777300ER (Thread starter):

That is a very easy calculation for you to work out yourself.

Being beyond the design range of all of aircraft by some margin, all of the aircraft you mentioned would be fuel volume limited. So all you need to look at is the published range payload curve to see if the aircraft can fly that far firstly, then lookup the maximum fuel volume and that will tell you the total burn.
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113312
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RE: Fuel Burn Of Quad Vs Twin

Fri Apr 08, 2016 3:46 am

I've been around aviation for more than 50 years. Only on Airliners.net do you ever hear of a four engined aircraft referred to as a "quad". You have twin engine planes, trimotor or three engined aircraft, and 4 engined aircraft. If you want to talk airplanes, use the jargon that people in the field use.
 
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RE: Fuel Burn Of Quad Vs Twin

Fri Apr 08, 2016 4:34 am

Quoting 113312 (Reply 10):

I've been around aviation for more than 50 years. Only on Airliners.net do you ever hear of a four engined aircraft referred to as a "quad". You have twin engine planes, trimotor or three engined aircraft, and 4 engined aircraft. If you want to talk airplanes, use the jargon that people in the field use.

https://leehamnews.com/2015/12/11/bjorns-corner-twins-or-quads/

http://www.askcaptainlim.com/-airpla...rsus-four-engine-plane-debate.html
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chrisMUC
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RE: Fuel Burn Of Quad Vs Twin

Mon Apr 11, 2016 9:46 pm

to get an idea, at my company we calculate standard (holding/extra) fuel burn of an A330-300 with 4.8 t/h, that of an A340-300 with 6.0t/h, that's 25% more.
Both types have exactly the same cabin layout.
If you compare the planned take off fuel for exactly the same flight, the difference is even bigger.
 
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Matt6461
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RE: Fuel Burn Of Quad Vs Twin

Mon Apr 11, 2016 11:19 pm

Quoting chrisMUC (Reply 12):
fuel burn of an A330-300 with 4.8 t/h, that of an A340-300 with 6.0t/h, that's 25% more.

As we've discussed previously in threads linked above, this is an apples-oranges comparison:

-A343 is built for much longer range than A333, especially at EIS. Range costs efficiency. A343, for example, carries extra MLG and empennage structure for the higher gross weight. That weight also impacts fuselage and wing weight.

-A343 has very poorly-matched engines. It was supposed to carry a GTF "superfan," but this project was cancelled. The replacement CFM56 derivatives are extremely heavy for their power. The A333's clean sheet Trents, optimized for its frame, also surely offer better SFC.

The better comparison is with the 77E. In the thread linked above, we discussed that Bjorn/Ferpe's numbers show that A343 being about equal to the 77E on cash operating costs.
 
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SEPilot
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RE: Fuel Burn Of Quad Vs Twin

Wed Apr 13, 2016 12:34 pm

From a theoretical standpoint, jet engines gain in efficiency as they get larger, for several reasons. First, losses at the blade tips get proportionally less as the fans and turbines get larger. Second, heat losses reduce because the surface area becomes smaller in proportion to the air volume. Also, temperatures can probably be allowed to get higher at the center of the flow for the same reason without critical parts overheating. In addition, the aerodynamic drag of two large engines will be smaller than of four smaller ones. But theory does not always work out as expected in practice. I do expect, though, that for equivalent technology that the same size and range airliner designed with two engines will be more efficient than one designed with four. And since there has never been an airliner designed with more engines than current technology required for the range and payload desired I think this proves my point.
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zeke
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RE: Fuel Burn Of Quad Vs Twin

Wed Apr 13, 2016 1:22 pm

Quoting chrisMUC (Reply 12):

Normal holding for flight planning is based upon 1500 ft

From PER-HLD

A330 4.8t/hr is holding for 160t @1500ft
A340 6t/hr is holding for 205t @1500ft

If you look at both types at [email protected] ft they have the same holding rate
A330 4.8t/hr (2396 kg/hr/eng)
A340 4.8t/hr (1200 kg/hr/eng)

If you look at both types at [email protected] ft
A330 5.5t/hr (2755 kg/hr/eng)
A340 5.6t/hr (1408 kg/h/eng)

Quoting Matt6461 (Reply 13):

You have no idea what you are talking about. You are not rated on either aircraft.
Human rights lawyers are "ambulance chasers of the very worst kind.'" - Sky News
 
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Polot
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RE: Fuel Burn Of Quad Vs Twin

Wed Apr 13, 2016 3:21 pm

Quoting zeke (Reply 15):
You have no idea what you are talking about. You are not rated on either aircraft.

You realize you are basically agreeing with him right?

ChisMUC's comparison (which he states was taken directly from his airline) was apples-to-oranges that involved more than just the difference between 2 and 4 engines.
 
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zeke
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RE: Fuel Burn Of Quad Vs Twin

Wed Apr 13, 2016 9:43 pm

Quoting polot (Reply 16):
You realize you are basically agreeing with him right?

No I was not. The A333/A343 has near identical holding rates for the same weight (even at MLW) all that rubbish about extra MLG and poorly matched engines is just made up by someone who has no idea what they are talking about.

The FCOM numbers I presented show virtually no difference between the two.
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Matt6461
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RE: Fuel Burn Of Quad Vs Twin

Thu Apr 14, 2016 7:35 am

Quoting zeke (Reply 15):
If you look at both types at [email protected] ft they have the same holding rate
A330 4.8t/hr (2396 kg/hr/eng)
A340 4.8t/hr (1200 kg/hr/eng)

If you look at both types at [email protected] ft
A330 5.5t/hr (2755 kg/hr/eng)
A340 5.6t/hr (1408 kg/h/eng)

Ugh.

Zeke you're comparing these aircraft at identical GROSS weight.
OF COURSE they have near-identical fuel burn at identical GROSS weight - they have near-identical wings and wetted area.

Quoting zeke (Reply 15):
You have no idea what you are talking about. You are not rated on either aircraft.

Great argument. How many of the A340 design team was rated to fly the A340?
Your persistent, repeated error is to presume that pilot rating rectified your innate deficiencies in logical reasoning.

My point about about the A330 and A340 relates to their EMPTY, not GROSS weights.

If the A340 really had the same fuel burn as the A330 how on earth did it sell so poorly?
Especially considering that the A333 knee-capped the 77E despite shorter range, while the 77E outsold the A343.

One might think these obvious empirical facts would cause some pause to your arrogance...
But I've "known" you well enough now not to be so hopeful.

[Edited 2016-04-14 01:22:43]
 
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zeke
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RE: Fuel Burn Of Quad Vs Twin

Thu Apr 14, 2016 9:53 am

Quoting Matt6461 (Reply 18):
Zeke you're comparing these aircraft at identical GROSS weight.
OF COURSE they have near-identical fuel burn at identical GROSS weight - they have near-identical wings and wetted area.

Yes I did compare them at gross weights, because we hold at gross weights. I also gave a large weight band from light weight to MLW (160-190t). The MLW on the A333 is 187t, and 190t on the A343. I have presented the numbers across the normal operating range, they are near identical.

Quoting Matt6461 (Reply 18):
Great argument. How many of the A340 design team was rated to fly the A340?

Probably around 50 by the time it was certified, pilots can be engineers, and engineers can be pilots.

Quoting Matt6461 (Reply 18):
Your persistent, repeated error is to presume that pilot rating rectified your innate deficiencies in logical reasoning.

What is a pilot rating ?

Since when is presenting manufacturers data, translate to "innate deficiencies in logical reasoning".
Human rights lawyers are "ambulance chasers of the very worst kind.'" - Sky News
 
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jambrain
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RE: Fuel Burn Of Quad Vs Twin

Thu Apr 14, 2016 3:31 pm

Quoting zeke (Reply 15):
If you look at both types at [email protected] ft
A330 5.5t/hr (2755 kg/hr/eng)
A340 5.6t/hr (1408 kg/h/eng)

Demonstrates quite how wrong some of the opinion pieces are when they blindly assert 2 engines are better then 4!

Zeke data shows only a 2% SFC penalty from a quad.

Also RR have said maintenance can be equal per unit of thrust!

Quoting RR:
"Four engines for the price of two (four Trent 500 = two GE90-115)".
http://www.flightglobal.com/news/art...lan-to-restore-a340-600-ap-393844/

If you plot fuel burn / second / thrust from the EASA databank:-
http://www.easa.europa.eu/document-l...aircraft-engine-emissions-databank

There is not an obvious trend that SFC improves with engine size!

I say bring back the supersonic quads!!
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RE: Fuel Burn Of Quad Vs Twin

Thu Apr 14, 2016 3:58 pm

Quoting zeke (Reply 19):
Since when is presenting manufacturers data, translate to "innate deficiencies in logical reasoning".

That has to be the line of the week!
"When I find out I was wrong, I change my mind. What do you do?" -attributed to John Maynard Keynes
 
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Matt6461
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RE: Fuel Burn Of Quad Vs Twin

Thu Apr 14, 2016 9:36 pm

Quoting jambrain (Reply 20):
Zeke data shows only a 2% SFC penalty from a quad.

Ok let me spell this out a little more.

Zeke's data is for an A333 and A343 at identical gross weights in holding.
Why is this the wrong comparison?
Because the A343's empty weight is ~15,000lbs higher than the A333.
To compare these aircraft at equal gross weight is to assume that the weight added to A343 over the A333 has no effect on drag and mission fuel burn.
Everyone sees that's a bad assumption, right?

Now it's true that both aircraft might be in a hold at 160t or 190t. In that situation, however, the A333 would be carrying more payload or fuel than the A343. So again this is an apples-oranges comparison.

To project the figures for identical-weight-hold across an entire mission, we'd have to assume that the A333 always tanks ~15,000lbs more fuel than needed (after reserves, contingency, etc.). That's obviously a stupid assumption. Maybe the A333 does it to protect her quad sibling from feeling overweight? Awe... cute.

Quoting zeke (Reply 17):
The A333/A343 has near identical holding rates for the same weight (even at MLW) all that rubbish about extra MLG and poorly matched engines is just made up by someone who has no idea what they are talking about.

And I guess Airbus has no idea what it's talking about when it published a significantly higher OEW for the A343 versus the A333. Must have been some of those non-pilot engineers doing the math, right?

Quoting zeke (Reply 19):
Since when is presenting manufacturers data, translate to "innate deficiencies in logical reasoning".

When do you do so in the transparently wrong way you've posted in this thread.

Try to answer one question - is the A343 heavier than the A333?

[Edited 2016-04-14 15:07:08]
 
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zeke
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RE: Fuel Burn Of Quad Vs Twin

Fri Apr 15, 2016 12:07 am

Quoting Matt6461 (Reply 22):
Why is this the wrong comparison?
Because the A343's empty weight is ~15,000lbs higher than the A333.
To compare these aircraft at equal gross weight is to assume that the weight added to A343 over the A333 has no effect on drag and mission fuel burn.
Everyone sees that's a bad assumption, right?

The problem is not in what I presented, it is you not knowing how aircraft are operated. It comes down to you not knowing what you are talking about.

Firstly the holding fuel flow is used in flight planning to determine the final reserve fuel which is 30 minutes of holding at 1,500 feet above the alternate aerodrome. It is based upon gross weight at the end of the flight plan, and it changes every flight plan. From experience I know the range of numbers which are normal for a given load.

Normally for the A343 they are operated near MTOW fly long distances and land, they are not operated at MZFW or MLW limits. The A333 however often can be flown at MLW or MZFW limits as they are flying shorter distances.

The gross weights for landing the A333 are often higher than the A343. This is due to the flights that are used on each type, the A343 being a long haul aircraft you are looting at the far right of the range/payload curve where payload if offloaded to put on fuel to get the range. The A333 is often flown in the range of the payload/range curve where even if you were to MZFW or MLW limited you would be still well below MTOW.

At the end of the flight, the trip fuel is burnt off, so the gross weight depends on the amount of payload carried as that does not change during flight.


Quoting Matt6461 (Reply 22):
When do you do so in the transparently wrong way you've posted in this thread.

There is nothing wrong with what I presented, the error is in your assumptions.
Human rights lawyers are "ambulance chasers of the very worst kind.'" - Sky News
 
WIederling
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RE: Fuel Burn Of Quad Vs Twin

Fri Apr 15, 2016 7:00 am

Quoting Matt6461 (Reply 22):
Now it's true that both aircraft might be in a hold at 160t or 190t. In that situation, however, the A333 would be carrying more payload or fuel than the A343. So again this is an apples-oranges comparison.

The A343 allows significantly more MTOW for more range. ( The structure fraction then actually is lower on the 343 )
Which turns your comparison admonishment into a spoilt fruit thing.

Same fuel for same weight indicates that the airframe/sfc/drag balance is the same. ( the airframe is exactly the same, the difference is reduced to drag/sfc difference from 4 CFM to 2RR/PW/GE engines. OEW differences do not go beyond the differing summ of engine weights.)

Finally and noted again: the Twin over Quad advantage is overstated. A very successfull meme campaign from Boeing.
Murphy is an optimist
 
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Matt6461
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RE: Fuel Burn Of Quad Vs Twin

Fri Apr 15, 2016 8:12 am

Quoting WIederling (Reply 24):
the Twin over Quad advantage is overstated. A very successfull meme campaign from Boeing.

If you had read my responses to the previous threads on Quad v. Twin (linked above), you'd know that I frequently advocate for the benefits of quads. Based on the publicly available info, I can't see a good argument for why any plane bigger than a 77W is better off as a twin.

Quoting zeke (Reply 23):


This entire post is irrelevant jibberish. Everybody on TechOps knows the ideas your post addresses.
Let's go back to the points that are actually in dispute.
I claimed that the A343 has a higher empty weight due to (mostly) engines and landing gear.
You responded:

Quoting zeke (Reply 15):
You have no idea what you are talking about. You are not rated on either aircraft.

This suggests that you somehow disagree (with AIRBUS) that the A343 has a higher structural weight than the A333.
So I then asked you whether you agree that the A343 is heavier, at typical OEW, than the A333:

Quoting Matt6461 (Reply 22):
Try to answer one question - is the A343 heavier than the A333?

...a question you ignored because you know you're indisputably wrong and want to change the topic.

So I'll repeat, Zeke:

Is the A343 heavier than the A333?
If so (there's no "if"), does the weight delta arise from MLG and engines (mostly) or from some other source, considering that each plane has the same wing and fuselage?

If you can't answer these questions, we should assume you're afraid of the challenge. Or - same thing - that you know you're wrong but would rather distract the forum with another irrelevant missive.
 
skyhawkmatthew
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RE: Fuel Burn Of Quad Vs Twin

Fri Apr 15, 2016 8:42 am

Quoting zeke (Reply 15):
If you look at both types at [email protected] ft they have the same holding rate
A330 4.8t/hr (2396 kg/hr/eng)
A340 4.8t/hr (1200 kg/hr/eng)

If you look at both types at [email protected] ft
A330 5.5t/hr (2755 kg/hr/eng)
A340 5.6t/hr (1408 kg/h/eng)
Quoting Matt6461 (Reply 18):
Zeke you're comparing these aircraft at identical GROSS weight.
Quoting zeke (Reply 23):
the gross weight depends on the amount of payload carried as that does not change during flight.

Zeke, given that, as you said, the fuel flow is near enough to identical at equal gross weights, what sort of payload is each aircraft carrying at that GW? There is quite a substantial empty weight delta between the A330/A340, which means at the same gross weight, the A330 will be carrying a fair bit more payload for the same fuel burn = $$$?
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Matt6461
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RE: Fuel Burn Of Quad Vs Twin

Fri Apr 15, 2016 8:48 am

Quoting skyhawkmatthew (Reply 26):
There is quite a substantial empty weight delta between the A330/A340, which means at the same gross weight, the A330 will be carrying a fair bit more payload for the same fuel burn = $$$?

Yeah obviously. It's another apples-oranges comparison.

...or the A330 is carrying 4x as much fuel as is necessary to hold, meaning it burns more fuel than is necessary during a given mission. None of it makes sense.
 
WIederling
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RE: Fuel Burn Of Quad Vs Twin

Fri Apr 15, 2016 9:55 am

Quoting Matt6461 (Reply 27):

napkin math:

The bare 343 airframe could actually be slightly lighter than the current A330.

CFM56: 4 x 3950kg ~=16t
Trent700: 2 x 4800kg ~=9.6t

delta 6.4t

A343 OEW ~= 130.1t
A333 OEW ~= 124.5t
delta 6.6t

center MLG ~= 1..1.5t ???
i.e. A343 has 8t more stuff for an OEW increase of 6.6t

( a difference that could be sunk in the seating  
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zeke
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RE: Fuel Burn Of Quad Vs Twin

Fri Apr 15, 2016 11:11 am

Quoting Matt6461 (Reply 25):
This entire post is irrelevant jibberish.

I am not going to respond to the flamebait.

Quoting skyhawkmatthew (Reply 26):
Zeke, given that, as you said, the fuel flow is near enough to identical at equal gross weights, what sort of payload is each aircraft carrying at that GW?

At MLW which is achievable for both aircraft on a shorter distance, the A343 would look at a payload of around 50t (around 30t of passengers and 20t of freight), and the A333 around 55t (around 35t of passengers and 20t of freight).

On a long haul flight the payload on the A343 will drop back to 30-35t and more likely landing around 160-170t. The reason for the lower payload as I mentioned above is you are now flying on the right hand side of the payload/range curve where payload is offloaded to get fuel on at MTOW.



For long haul operations the catering on the A343 can be 1t higher for an extra meal service than a regional. Sometimes on a regional return sector catering and/or fuel is taken. Our A333s have different configurations from 251 seats to 317 seats with no crew bunks. The A343 we have configured with 265 seats, and two bunk areas.

Quoting skyhawkmatthew (Reply 26):
There is quite a substantial empty weight delta between the A330/A340, which means at the same gross weight, the A330 will be carrying a fair bit more payload for the same fuel burn = $$$?

The weight difference is overstated mainly by people who dont take into account the difference in configurations between a long haul and short/medium haul cabin. The actual empty weight difference is in the order of 3-4t, however the underfloor crew rest on the A340 is over 900 kg, additional crew rest in the cabin, we carry extra water for the longer flight time, have additional catering, additional emergency equipment. Say if both aircraft had the same payload, the A333 landing at 160t, and the A343 at 165t, the difference in holding fuel is negligible. The A333 would burn 2396 kg/hr/eng and the A343 1235 kg/hr/eng, less than 150 kg/hr difference between the two (not the 1.2t per hour as reply 12). To put that in perspective we typically allow 500 kg to taxi for takeoff.
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cloudboy
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RE: Fuel Burn Of Quad Vs Twin

Sun Apr 17, 2016 2:28 pm

So let's drop the comparison between 330 and 340 for arguments sake. For the argument that a 4 engine plane uses more fuel than a 2 engine plane, what causes that extra fuel burn? Is there a waste in thrust? Is there an overhead cost in fuel to just having the engine spinning?
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RE: Fuel Burn Of Quad Vs Twin

Mon Apr 18, 2016 3:28 am

Quoting BG777300ER (Reply 2):
Interesting point. Can you elaborate on some of these? I am looking to understand why there is such a huge movement of airlines to go from 4 to 2 engines. The answer I keep hearing is "fuel efficiency $$$ savings".

I would think that both types could be roughly equal in fuel efficiency - the main savings would not be fuel, but the simple fact that you have only 2 engines to maintain, rather than 4. Engine maintenance cut in half right there.
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jambrain
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RE: Fuel Burn Of Quad Vs Twin

Mon Apr 18, 2016 8:18 pm

Quoting Dreadnought (Reply 31):
I would think that both types could be roughly equal in fuel efficiency - the main savings would not be fuel, but the simple fact that you have only 2 engines to maintain, rather than 4. Engine maintenance cut in half right there.

Not true

RR say they charge 1/2 as much per engine for the smaller engine:-
"Four engines for the price of two (four Trent 500 = two GE90-115)".
http://www.flightglobal.com/news/art...lan-to-restore-a340-600-ap-393844/
Jambrain
 
kurtverbose
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RE: Fuel Burn Of Quad Vs Twin

Mon Apr 18, 2016 8:53 pm

Yes, bigger engines cost more to maintain than smaller engines. They have far more compressor and turbine blades for a start.
 
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Matt6461
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RE: Fuel Burn Of Quad Vs Twin

Tue Apr 19, 2016 9:04 pm

Quoting zeke (Reply 29):
I am not going to respond to the flamebait.

What a marvelous personal transformation must have taken place! So I'm sure we won't see any more of this:

Quoting zeke (Reply 17):
made up by someone who has no idea what they are talking about.
Quoting zeke (Reply 23):
It comes down to you not knowing what you are talking about.


Fellow a.netters, I'm not even sure what the grounds of disagreement between me and Zeke are/were. As another poster notices, he seems to be agreeing with me. But let's try to figure this out anyway:

If he is merely saying that a twin and a quad at equal gross weight will have practically equal fuel burn, then there's no disagreement.

Given his accusations about my knowledge, however, the only rational interpretation seems that he thinks either (1) the A343 doesn't weigh more than the A333 or (2) the differences in their actual operating weights are solely attributable to the A343's long configuration versus the A333's midhaul configuration.

(1) flatly contradicts Airbus' own figures and all common sense. Range costs something - else all planes would be ULH'ers.

(2) is a slightly more subtle response but the principle of (1) still applies: Were the only difference between A333 and A343 weight attributable to configuration, then why didn't Airbus make the A333 capable of being configured like the A343 and operating its missions?

The only answer to this is that the A333 would have been a heavier, costlier plane in that case.

Can anybody seriously disagree with this?

I'm not even sure Zeke disagrees. I suspect he wanted to attack but didn't bother to think through what he was attacking in the first place.
 
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zeke
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RE: Fuel Burn Of Quad Vs Twin

Wed Apr 20, 2016 5:38 am

Quoting Matt6461 (Reply 34):
What a marvelous personal transformation must have taken place! So I'm sure we won't see any more of this:

You just cannot help yourself with underhanded insults.

Quoting Matt6461 (Reply 34):
(1) the A343 doesn't weigh more than the A333 or (2) the differences in their actual operating weights are solely attributable to the A343's long configuration versus the A333's midhaul configuration.

Refer to

Quoting zeke (Reply 29):
The weight difference is overstated mainly by people who dont take into account the difference in configurations between a long haul and short/medium haul cabin. The actual empty weight difference is in the order of 3-4t, however the underfloor crew rest on the A340 is over 900 kg, additional crew rest in the cabin, we carry extra water for the longer flight time, have additional catering, additional emergency equipment. Say if both aircraft had the same payload, the A333 landing at 160t, and the A343 at 165t, the difference in holding fuel is negligible. The A333 would burn 2396 kg/hr/eng and the A343 1235 kg/hr/eng, less than 150 kg/hr difference between the two (not the 1.2t per hour as reply 12). To put that in perspective we typically allow 500 kg to taxi for takeoff.

I have provided the actual holding rates between the long haul and short/medium haul configurations. If the A340 was solely used for short/medium haul configurations the crew rests could be removed, less water/water waste storage would be required, and you could get rid of the takeoff gear that is solely there for the higher MTOW ( we can have it stowed for lower takeoff weights, often you will see it not even touching the ground at lighter weights).

Again clearly demonstrating you have no idea what you are talking about.

Quoting Matt6461 (Reply 34):
(1) flatly contradicts Airbus' own figures and all common sense.

You have not presented any of the manufacturers data, and you have provided no common sense as I have yet to see a post of yours where you consider airlines actually fly aircraft around with payload. I have directly shown that either with the same gross weight (i.e. with the wide payload band that gives you a LW of 160-190t), or with the same payload (35t) the fuel burn difference in a hold is next to nothing, less than our taxi fuel.

I have also clearly explained where on the range payload curve these aircraft normally are tasked.

Again clearly demonstrating you have no idea what you are talking about.

Quoting Matt6461 (Reply 34):
Range costs something - else all planes would be ULH'ers.

To get the additional range the A343 has over 40t high MTOW and more than 40,000 liter fuel capacity. The A333 has the same center tank, it has not been used in the past. The latest A333s have the center tank (like the A332) and the same fuel capacity option as the A343.

Again clearly demonstrating you have no idea what you are talking about.

Quoting Matt6461 (Reply 34):
then why didn't Airbus make the A333 capable of being configured like the A343 and operating its missions?

They do, these are customer options. The underfloor crew rest on the A330/A340 is a container that is loaded in the aft cargo hold. Activating the center fuel tank is a customer option, main deck crew rests is a customer option, fuel jettison is a customer option, the size of water/waste tanks is a customer option, the galley configuration is a customer option.

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Again clearly demonstrating you have no idea what you are talking about.

Quoting Matt6461 (Reply 34):
The only answer to this is that the A333 would have been a heavier, costlier plane in that case.

Airlines configure the aircraft the way they want it to meet their proposed routes. They do not buy unnecessary options to incorporate unused capabilities. Airlines purchased the A330 and A340 for different routes.

Again clearly demonstrating you have no idea what you are talking about.
Human rights lawyers are "ambulance chasers of the very worst kind.'" - Sky News
 
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atcsundevil
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RE: Fuel Burn Of Quad Vs Twin

Wed Apr 20, 2016 9:29 am

There has been some good information shared in this thread, but I feel I should remind users that being disrespectful of others in the forums is unacceptable. We can all find a way to debate the topic rather than the person. Let's focus on continuing the discussion and refrain from openly attempting to discredit others. We're all here because we love aviation, so there's no reason for any hostilities  

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kurtverbose
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RE: Fuel Burn Of Quad Vs Twin

Wed Apr 20, 2016 8:14 pm

I think it's pointless comparing existing quad's and twins as you end up arguing that they're not the same - which this thread proves. How many twins have a directly comparable quad for the same mission and same tech level?

None.

It's at a theoretical level this discussion should happen at.

Lightsaber posted the advantages of larger engines - I think one issue is the tip losses are proportionally less. Maintenance costs depend on the engine. The CFM powered A340's used a fairly cheap narrowbody engine made in huge numbers.

Historically, aeroplanes have used as few engines as possible, but one thing that intrigues me is if this will continue? With bypass ratio's increasing and assuming engines remain underwing mounted, will 4 smaller engines get an advantage over 2 engines but very long landing gear?
 
flipdewaf
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RE: Fuel Burn Of Quad Vs Twin

Fri Apr 22, 2016 7:37 pm

Quoting Matt6461 (Reply 25):
Is the A343 heavier than the A333?

The real question surely is what part of the difference in weight is due to 4 engines and what part is due to it being a longer haul aircraft but I'd guess those can be independently quantified.

Fred
Image
 
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zeke
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RE: Fuel Burn Of Quad Vs Twin

Sat Apr 23, 2016 12:50 am

Quoting flipdewaf (Reply 38):
The real question surely is what part of the difference in weight is due to 4 engines and what part is due to it being a longer haul aircraft but I'd guess those can be independently quantified.

I will break it down for you

A343 Inboard Engine Pylon and Nacelle Equipment

Inlet cowl 143
Fan cowl 75
Thrust reverser 438
Primary nozzle 113
Centre body 95
Pylon 883
Engine 2633

Total 4380 kg

A343 Outboard Engine Pylon and Nacelle Equipment

Inlet cowl 143
Fan cowl 75
Thrust reverser 438
Primary nozzle 113
Centre body 95
Pylon 912
Engine 2633

Total 4409 kg

Total mass of Engine Pylon and Nacelle Equipment 17578 kg

Center landing gear 844 kg

A330 PW 4168A - Pylon and Nacelle Equipment

Inlet cowl 216
Fan cowl 143
Thrust reverser 778
Exhaust nozzle 80
Pylon 1260
Engine 5867

Total 8344

Total mass of Engine Pylon and Nacelle Equipment 16688 kg

A343 engines and pylons are 890 kg heavier add the centre landing gear 844 kg makes the A343 airframe essentially only 1734 kg heavier and capable of 40+ tonnes higher MTOW.
Human rights lawyers are "ambulance chasers of the very worst kind.'" - Sky News
 
kurtverbose
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RE: Fuel Burn Of Quad Vs Twin

Sat Apr 23, 2016 6:43 am

Quoting zeke (Reply 39):
A343 engines and pylons are 890 kg heavier add the centre landing gear 844 kg makes the A343 airframe essentially only 1734 kg heavier and capable of 40+ tonnes higher MTOW.

And does it with slightly less thrust - impressive.
 
WIederling
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RE: Fuel Burn Of Quad Vs Twin

Sat Apr 23, 2016 7:46 am

Quoting kurtverbose (Reply 40):

You see the 3 of 4 versus 1 of 2 effect of minimum climb on engine out requirements.(?)

Same thing gives Twins the "rocket properties" of high climb rates under regular engine use.
Murphy is an optimist
 
DfwRevolution
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RE: Fuel Burn Of Quad Vs Twin

Sat Apr 23, 2016 3:53 pm

Quoting WIederling (Reply 24):
Finally and noted again: the Twin over Quad advantage is overstated. A very successfull meme campaign from Boeing.

Indeed. Boeing's marketing was so successful, they convinced Airbus to launch a twinjet to replace the A340.

I suppose you also forgot that it was Airbus, not Boeing, who launched an entire advertising campaign to convince the market that their engine configuration was superior. Remember "4 Engines 4 Longhaul?" Boeing wasn't taking out magazine articles, repainting aircraft, and hiring spokesmen, but Airbus sure did.
I have a three post per topic limit. You're welcome to have the last word.
 
WIederling
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RE: Fuel Burn Of Quad Vs Twin

Sat Apr 23, 2016 5:59 pm

Quoting DfwRevolution (Reply 42):

priceless. That critique from the land of "over and/or mis-stating your capabilities" is the norm  
Murphy is an optimist
 
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DocLightning
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RE: Fuel Burn Of Quad Vs Twin

Sat Apr 23, 2016 6:53 pm

Quoting skyhawkmatthew (Reply 26):

Zeke, given that, as you said, the fuel flow is near enough to identical at equal gross weights, what sort of payload is each aircraft carrying at that GW? There is quite a substantial empty weight delta between the A330/A340, which means at the same gross weight, the A330 will be carrying a fair bit more payload for the same fuel burn = $$$?

I'm always amused when people claim that the A330/A340 is not a good twin/quad comparison.

If not that pair, then which pair? The A340 is literally a four-engined A330. Yes, there are necessary differences between the airframes, including the addition of a center gear, but no other twin/quad pairs come remotely as close as these two models.

So if the A330 burns less fuel at the same payload, which is a lower gross weight, then that pretty much demonstrates the issue with quads.
-Doc Lightning-

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Starlionblue
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RE: Fuel Burn Of Quad Vs Twin

Sun Apr 24, 2016 7:02 am

Quoting DocLightning (Reply 44):

If not that pair, then which pair? The A340 is literally a four-engined A330. Yes, there are necessary differences between the airframes, including the addition of a center gear, but no other twin/quad pairs come remotely as close as these two models.

So if the A330 burns less fuel at the same payload, which is a lower gross weight, then that pretty much demonstrates the issue with quads.

Except the 330 can't fly nearly as far with that payload as the 340. If the 330 had the same max MTOW as the 340 then they would be exactly comparable. You'd need to hang much more powerful engines on the 330 to make an exact comparison. And it still wouldn't be exact.
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Dehowie
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RE: Fuel Burn Of Quad Vs Twin

Sun Apr 24, 2016 1:55 pm

For all this talk about just how awesome the A340 is something has been missed.
There are over 300 A330's still on back order yet A340 production finished 5 years ago.
I think those figures alone indicate the relative merits of the individual aircraft.
Most airlines have withdrawn the 340 yet the A330 thrives.
So plucking figures to make the 340 look good is all good but does not hold water in the real world.
Simply the 330 is very hard to beat..
2EOS1DX,EF14.2.8LII,17TS,85/1.2,16-35L,24-70LII,24L,70-200F2.8LII,100-400,300/400/500/800L
 
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lightsaber
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RE: Fuel Burn Of Quad Vs Twin

Sun Apr 24, 2016 3:13 pm

If there really wasn't a fundamental difference in operating economics, we would have seen an A340NEO. There are fundamental reasons. For a given level of engine technology:
1. There is more wet area in the 4 engines of a quad than the 2 engines of a twin. By that I mean the compressor, turbines, combustors, and nacelle. Wet area is area the air touches. As the fast moving air moves past the wet area, there is drag and that is lost fuel efficiency.
2. The blade tip clearance is a technology level. The larger the engine, the less the blade tip clearance causes losses. This allows larger engines to have a higher pressure ratio than smaller engines. For a given airframe size, a twin benefits from this (less loss due to blade tip clearances being a smaller fraction of core flow and the allowed higher pressure ratio).
3. Weight. A quad must duplicate systems. While there is some benefit to wing bending moment reduction and shorter landing gear, the weight advantage will always favor the twin.
4. Maintenance is complicated. For the CFM-56, it benefited tremendously from the HUGE economies of scale of the massive CFM-56 economies of scale. But if it is a custom engine... bad economies of scale.

Quoting roseflyer (Reply 3):
Guessing fuel burn for airplanes that haven't even been built yet is not easy.

We've gotten pretty good. The last new airframe I worked on met fuel burn with weight within 1%. SInce 2% is the typical margin, we were very happy. Now Pratt has missed fuel burn on a lot of engines in the past (too many to list), the PW1100G was made conservative enough it beat promise. (Pratt applied more GE style engineering approach, but not far enough IMHO on subsystem design.)

Quoting Flighty (Reply 5):
Twins have less maintenance. Around "15%" less fuel burn (using Airbus A330/A340 as a quasi example). Which is a massive number. Fewer engines to purchase.

Twins do have less maintenance. But 15% lower fuel burn is high. For the same technology, it should be about 7% less fuel burn. The issue is we have no true same technology quad vs. twin. The A343 was handicapped by engines of less technology than the 77E and certainly the 77W.

Quoting 113312 (Reply 10):
I've been around aviation for more than 50 years. Only on Airliners.net do you ever hear of a four engined aircraft referred to as a "quad".

Twin vs. Quad is aerospace engineering terminology.

Quoting Matt6461 (Reply 13):
-A343 is built for much longer range than A333, especially at EIS. Range costs efficiency.

Range does have a cost. But as efficiency improves, much less. The A339 still has empty centerline tank volume so any MTOW increase will be further range increase. But the A339 is older technology than the 789 or A359... The market has moved on.

Lightsaber
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Dehowie
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RE: Fuel Burn Of Quad Vs Twin

Mon Apr 25, 2016 12:03 am

As the 330 is a mid range aircraft and the 340 a long range one they where designed to compliment not compete.
Rather than comparing figures between those aircraft the 777 and the 340 would of been a better comparison.
The thing which killed the 340 was the relaxation in the Etops requirements.
The 777 which Boeing placed all its money on was a gamble which paid off very handsomely.
However the extension of Etops requirements was done over time as the airframe matured as did its engines.
As Etops times crept up it was eating into the territory traditionally operated by 4 engine aircraft opening up new routes and efficiencies for airlines and wonder Boeing lobbied so hard for the big numbers that exist today and why they avoided a new 4 engine airframe.
Don't build a new frame buy off the regulator.
The FAA being either blind stupid or both or being heavily bought thought it was somehow reasonable to issue a brand new airframe using an entirely different manufacture process and all new technology an 330 minute Etops approval.
With another AD coming out on the 787 for Furher engine ice issues it would seem there is massive political pressure to issue huge Etops approvals on untested new technology aircraft that just happen to be locally built.
The FAA have a lot to answer giving the 787 an Etops approval of 330 minutes yet numerous engine failures still occurring today in far greater numbers than aircraft with far less technical issues.
The huge Etops numbers killed 4 engine aircraft over the last 15 years no other single change opened more routes to the twin jet that where traditionally banned to all except three and four engine airframes.
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Florianopolis
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RE: Fuel Burn Of Quad Vs Twin

Mon Apr 25, 2016 3:18 am

Quoting Dehowie (Reply 48):
Don't build a new frame buy off the regulator.

The FAA have a lot to answer giving the 787 an Etops approval of 330 minutes

Eh, remember that the airlines love this as much as the manufacturer. In fact, there is no constituency opposed to this.

Maybe the FAA dropped the ball on the battery, but let's not get carried away about the engines.

If I may defend the regulators: On the 787 batteries, it's actually much more likely that they simply didn't know what they were doing than that they were bribed.

Boeing comes to them with a battery, which the FAA simply has no idea how to certify, and even if they did, all the people who are expert on the technology work at Boeing. So they ask Boeing if it's good, Boeing says "totally cool, guys", and that's that.

Question for you, out of curiosity: Do you believe that ETOPS requirements being applied to aircraft with more than two engines is because of Boeing lobbying?

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