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KevinAu

The case for 4-engine planes - whats the advantage?

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Hello fellow Avsimmers :)Sorry if this is a bit of a goofy issue but its been on my mind and I wanted to share it with you all.In a nutshell - what justifies the cost of a 4-engine airliner in todays world? Why A340-500 or B747 instead of A330 & 777? With an A340/747 you got two more engines to maintain etc.Todays big twins can fly far - as far as if not further than the quads. If Im not mistaken the 777-200LR can fly further than the A340s.Lastly the reliability of modern turbofans is execptional - theres more twins over the Atlantic than quads. Im not saying that there have not been inflight shutdowns but those cases are rare.Do airlines pick quads because passengers feel safer in a 747-400 over the Pacific instead of a 777? I dont know if this true but I seem to recall Virgin Atlantic doing a passenger survey that came out in favour of quads on long-haul routes.But yeah thats it...from a costs & reliability perspective only: in todays world wouldnt you save money by having a twins-only fleet? The days of unreliable engines is over so why pay for and have the headache for two more engines hanging on the wings?Thanx :)

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Whoops I forgot to add that the obvious choice for quads would be more direct routeings because they are not burdened by ETOPS rules.

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This is Business 101An airline picks a route, and then guesses how many tickets they can sell for that route. Then they create a list of the aircraft that have the needed range and can carry that many passengers. For the aircraft on that list, they compute the profit they'll make per passenger, and they pick the aircraft that gives the highest rate of return.The only thing that matters to the airline is profit per passenger. I've oversimplified some of the terms above - for example, if you think you're going to sell a lot of tickets, a 777 might seem too small at first, and might not be on the "acceptable aircraft" list, you might consider buying two 777's instead. It's a complicated process, but it all comes down to one simple concept: an airline tries to figure out what aircraft gives them the most profit per passenger. That's all this is about.Under certain conditions, an A380 or a 747 will give an airline more profit per passenger than any other plane. That's the only reason any airline will buy one. Not for looks, not because people think it's cool (well, maybe Virgin Atl would :) ). The conditions under which you'd buy a big four engine beast are: very high volume over medium or long-range distances. For those routes, a big plane is the way to go. For lower volume routes, you have to buy a smaller plane like a 777, because for those routs, if you bought an A380 it would be flying empty most of the time and actually losing money. A 777 no doubt gives you less profit per passenger than a bigger plane, but if the volume of a route is low your only options are a) take the lower profits, or :( don't fly the route and get zero profits. On the other hand, if the passenger volume is so high that one 777 can't do the job, you could buy a second 777. But you'll save a lot of money by instead buying a single 747. Then you only have to pay the salaries of one flight crew and you only have to maintain one aircraft. So in that case, you make more money with a 747.See how it works?

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enave - Thank you for that detailed reply. :)As you may have guessed I do not have a "business head" so your answer is doubly fascinating and interesting to me. I had a feeling that it involved something along these lines but I admit that part of me still believed that some airlines opted for 4-engines because of safety issues (engine failure over the middle of the Pacific etc.)Thanx again!!

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Airline Business 102One other area to think about is the actual cost of aquiring of new aircraft and the lead time involved. It is very painful financially to aquire new equipment only to turn around and park them in the desert due to an economic down-turn. New aircraft still have to be paid for by somebody, be it leasing agent or the airline itself. If the airline has "older-yet paid-for" equipment it isn't as costly to park since there is no debt of aquisition to service.If you news-google "Northwest Airlines" for example there is an interesting article talking about how it kept the aged(and owned/paid-for) DC-9 fleet instead of going into more debt buy aquiring newer planes(a319-320, 340) at a faster rate than they are. NWA is known to be tight with a buck and very conservative....it is also not in bankruptcy (knock on wood).Airline finance is a juggling act and done with computers, bankers, lawyers, smoke and mirrors its seems. What seems to be simple gets very complicated.Tim__757

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Generally speaking:You have to realize the 747 is a 1960's design. Back then the order of the day relevant to the power output of the engines was redundancy amongst other certification rules for over water flights.Now that engines can produce more power more efficiently the trend is to reduce pilot workload as well as overall maint. costs. This brings us into the 757/767/777 era and ETOPS certification rules. When you can accomplish the same with 2 engines why have 4?The general aviation arena is also seing this trend. The Pilatus competes directly with the King Air. If it was me I'd opt to save the money and have roughly the same range and payload capabilities and have more cabin space with the Pilatus. The Pilatus is probably also 10X easier to fly given the pilot doesn't have to worry about having to keep 2 power levels at different settings and monitor 2 sets of gauges. The overal cost savings have to be awesome with only 1 engine and prop to TBO, + the engine outs are probably much easier to handle being that you wouldn't have dead weight on 1 wing.These are known as super singles. Fedex also does the same thing with the Cessna Caravan.Just some thoughts here.

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"A 777 no doubt gives you less profit per passenger than a bigger plane"Are you suggesting that a Boeing 777 is not a large plane ?:-hmmm Chris Low.

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The cost of using four engines instaed of two is born out by the increased safety issue.Try it yourself and you will soon realize that suffering a bird strike in one of four engines isn't the kind of emergency that is relevant to a twin engined aircraft and battling with the resultant 'yaw' that would follow.Another aspect to consider is that although it MAY be more costly to maintain four engines the fact that multi engines do not suffer the fatigue that a one of twin engines do and therefore last longer. To say nothing of the added power and tractability that multi engines provide.The safety record of the '747' is a statement to that reliabilty aspect.All the best,Dave.'Three greens and soft landings'

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>"A 777 no doubt gives you less profit per passenger than a>bigger plane">>Are you suggesting that a Boeing 777 is not a large plane>?:-hmmm >Which part of my statement sounds like, "a 777 is not a large plane" to you?

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The 777 is also designed to fly on 1 engine as are most twins. The 777's engines were also tested with gravel, birds, and other foreign material being ingested into them.There's nothing wrong with the 747 but the newer planes are just using the latest technology as was the 747.

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Thanks everyone for your information and views on this topic. Had a good time reading all of it :)I would like to admit that personally it IS comforting to look out of the windows and see two engines hanging on each wing when you are over the wide ocean!!!!Not that I would refuse to get on a twin for an ocean-hop but somehow the idea of just one turbofan holding you up if the other conks out is a bit unsettling (even when I know the super-reliability of those things!)

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>for 4-engines because of safety issues (engine failure over>the middle of the Pacific etc.)>If you listen to Airbus' propaganda this is what they hammer at - use 4 engines on Pacific/Atlantic routes. This is primarily to convince buyers not to buy the very economical 777 and purchase A-340 instead. But in fact ETOPS operation have been very safe and engines these days are extremely reliable. There is perhaps a single case of this Tahitian airline that flies between Tahiti and Japan and using twin engine say 777 would make routing (far from land) very difficult to satisfy ETOPS regulations. So being French no wonder they picked A340. In this case it is a better choice. But 98% of world routes are so close to land that two engines are fine. Don't listen to Airbus propaganda ;-)Michael J.WinXP-Home SP2,AMD64 3500+,Abit AV8,Radeon X800Pro,36GB Raptor,1GB PC3200,Audigy 2

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It would depend on which you are comparing. If you are comparing the 777 against the A340, the only advantage that the A340 has over the 777 is the sticker price. On a typical long range mission the 777 will do it 30 minutes faster and carry 10,000+ lbs. more payload while burning 20,000 fewer lbs. of fuel.

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Not to mention not requiring vomit removed from the cabin on such a regular basis... the A340 has a vile ride in turbulence. The A340 is the worst current-production airliner for passenger comfort, in my opinion, which makes me really wonder about the A380.

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The A340 (at least the 200 and 300) are heavily underpowered.If you've ever seen one trying to get off the ground you'd not want to fly one because of that alone, never mind the passenger comfort.

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