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Four-engine Jetliners

Sun Feb 11, 2001 1:48 am

I would to ask for any & all opinions regarding the four-engined jetliners still in production....such as the 747, A340 & the new A380. Do you think these aircrafts are dinosaurs now?? There are no three-engined aircraft being produced anymore & the 777 seems to be the ultimate in twin-engined fuel economy. The 777-300 can carry just as much as a first generation 747 now.
My personal theory that all four-engined jetliners are just simply gas guzzlers. Any thoughts?? Regards.
"Beer is living proof that God loves us and wants us to be happy." --Ben Franklin
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RE: Four-engine Jetliners

Sun Feb 11, 2001 2:13 am

I guess there is reasons why there are 4 engined jets.

Maybe you sould contact Airbus and Boeing and report your findings.

Isn't there something to do with ETOPPS or something like that?

I think it has to do with safety and weight capacity, I'm not too up to date with the 777 but if it can hold more cargo and pax's than I could be wrong.

The only thing is that there must be a good reason for these 4-engined jets.

It would make more sense to make a 3 engined jet to replace, as you said "4 engined gas guzzlers". Reduce the engines by 25%, but there will be a lack of performance, ie fuel economy reduced.

Don't engines burn less fuel at lower RPM's, so if this is true more engines running slower burn less fuel than two at high RPM's, as well as wear and tear on the engine, it might be cheaper to run the engines at a lower RPM so they will last longer and have less maintenance.

Just my thoughts, hope they help,

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RE: Four-engine Jetliners

Sun Feb 11, 2001 2:32 am

With the introdduction of the 777, ordes for the 747 have dropped. The 777 offers better economics than the 747. ETOPS is really not all of that big of a deal. You can not have the same mechanic work on both engines, and from no-matter where you are in the world, you are three hours from another airport. SFO-SYD could easily be done in a 777. If they have an engine failure, they can divert to Hawaii, Mexico, or one of the many islands in the pacific.

RE: Four-engine Jetliners

Sun Feb 11, 2001 4:06 am

 Nuts Mabe like on the A380 they need 4 engines for power.
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RE: Four-engine Jetliners

Sun Feb 11, 2001 4:16 am

4 engines have advantages and disadvantages. An example: twins are owerpowered, for safety reasons, quads not. ETOPS is another issue.

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RE: Four-engine Jetliners

Sun Feb 11, 2001 6:24 am

Look at what's the fastest commercial airliner flying today. Just look at the 747 which flys close to .9 mach. From this point of view I think the four engine aircraft gets a little more power than the twin. Besides the 777 engine is the most expensive engine out there, it costs alot more to replace it than any other engine types. And what happens if both engines failed, on the quad you would still have two more engine. Not quite so for the twin eh.
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RE: Four-engine Jetliners

Sun Feb 11, 2001 6:50 am


In regards to your comment about if 2 engines on a twin fails. What if 4 engines fails on a Quad? The chances that 2 engines of a quad failing is about the same as 4 on a quad = not likely.

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RE: Four-engine Jetliners

Sun Feb 11, 2001 8:08 am

Just a quick comment on the statement that 2 engines are as likely to fail as 4 and the various advantages etc.
I would say there are numerous considerations:
Twin engines provide better economy for a few reasons, main one is less drag i.e. two less pylons, nacelles etc. Therefore less fuel costs. It Can provide some service cost reduction as well.
Some people think the ETOPS stats on expected engine failure rate are a little skimpy, when, for example, engine failure that happen during take-off e.g. the EK 777-300's RR Trent that shed a blade the other day, are not taken into the ETOPS engine failure stats because it did not happen within an ETOPS segment of the flight plan....hmmm.
Going to a non-ETOPS twin, boeing at one point apparantly listed in-flight engine shut-downs on 737's as 'sub-idle conditions...'
I guess you could also look at uncontained engine failures, where it can be pot-luck where the debris ends-up....take-off in a twin, get an uncontained engine failure that takes out the other engine....bad news. (Never happened I believe).
Assuming an engine failure on a twin, the amount of damage to that engine could affect its drag, e.g. if it can't wind-mill...also nasty if stuck near the upper limit of the ETOPS requirement from a suitable runway. this could possibly cause problems in the viability of reaching that runway, you must remember that, for example, a 777 on one engine will drop to about 10,000', while having the rudder deflected to avoid unwanted yaw caused by asymettrical thrust, makes you wonder somewhat with all that drag the fuel requirements.
Some aircraft need 4 simply due to power requirements as stated already.
I guess in the end money rules, so if you can get away with a twin, it is the way to go. People could argue for a long time about which is better, 2/3/4 engines, no definate answer I would say, as there are so many factors to take into account (not just safety)
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RE: Four-engine Jetliners

Sun Feb 11, 2001 8:31 am

Come on now folks!

4 Engine jets just look better plain and simple. I wish commercial airlines felt the same way I do.

The A340, 747, IL-96 and all other quads in service just looks better.
I see no big deal about the 777. It looks like a 737 on steroids.
Just look at these pictures and compare:

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Photo © Darcy Stevens

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Photo © Peter Vercruijsse

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Photo © Brian Wilkes

Look at that boring twin in the background.

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Photo © George W. Hamlin

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Photo © Stefan Sjögren

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Photo © Eduard Brantjes

Put me on the dinosaur anyday.
Bring back the Concorde

RE: Four-engine Jetliners

Sun Feb 11, 2001 4:46 pm

Oh boy where do i begin...... lets see.

ILUV767, ETOPS is a big deal, try introducing it into an airline and you will see what i mean.

Gerardo, twin engine aircraft are overpowered on takeoff because they have to be able to complete the takeoff on one engine. quads base their calculations on 3 engines, therefore less power per engine is required.

Spaceman, Mach 0.9, ouch, care to tell me which operator flies at this speed on a regular basis?

B767-400er, remember the AC767 Glider, or the L1011 glider or even the BA 747 Glider? The chances of total engine failure may be "unlikely" but it does happen.

Tom775725, ETOPS requirements do account for IFSD in all cases, it doesnt have to be in the ETOPS area. You also talk about the twin engine aircraft having to come down to 10,000 feet following an engine failure, actually it doesnt, this is only required for depressurization, the fuel requirements for ETOPS take this into account. However if you are flying a quad and suffer a depressurization, there is no preflight planning on the amount of fuel that you need. Therefore you could argue that the twin is safer than the quad!

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RE: Four-engine Jetliners

Sun Feb 11, 2001 9:00 pm

Hi Ambasaid,

Sorry 10,000 was a bad comment,
I thought that with 1 engine, for example, a 777 with one engine running at max continuous, usually will travel along at about 12,000' - certainly a 777 I was on that lost 1 engine about 1 1/2 hours from JFK, immeadiatly droped to 12,000 feet (as shown on the flight info thing...) Then cruised along at that altitude until decending into JFK.
Cheers for the info about ETOPS, does an engine failure during takeoff that leads to RTO count as an IFSD as it isn't really an IFSD?? My info came from a DC10 capt who I guess doesn't really have to worry about ETOPS much!!

RE: Four-engine Jetliners

Sun Feb 11, 2001 9:53 pm


A 777 on one GE90-90B engine is easily able to maintain over 20,000 feet depending on weight.

At least for us, an IFSD is anytime that the engine stops doing what it was designed to do. So an engine failure on takeoff is a IFSD, but low oil pressure forcing you to retard the throttles and land with the engine at idle power is not!
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RE: Four-engine Jetliners

Sun Feb 11, 2001 11:55 pm

I don;t think we anywhere near to seeing a double-decker plane with two engines.
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RE: Four-engine Jetliners

Mon Feb 12, 2001 1:40 am

When comparing the efficiency of the 777 versus the 747, I think the wing design is a much bigger factor than the engines.

Wing Design is the main factor in comparisons between the 747 and A340.

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