leelaw
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The Ongoing Two Engines Vs. Four Debate

Sat Feb 10, 2007 6:29 pm

From James Wallace's, the Seattle P-I's aerospace reporter, blog:

"Airbus A340 debate: two engines vs. four"

Quote:
Airbus continues to make the argument, in trying to find customers for its slow-selling, four-engine A340, that four-engine jets are safer than those with two engines when it comes to long-haul flights...

http://blog.seattlepi.nwsource.com/aerospace/archives/111378.asp

Wallace asks why Airbus continues to beat the drums on this old debate about two-engine safety? Is anyone still listening?

In this specific instance, perhaps Mr. Leahy believes there are some "fat-cat" buyers of large VIP-luxury aircraft with whom the tenor of the "four engines for long haul" argument still strongly resonates, i.e. they feel "safer" with four engines? Anyone who can afford to purchase a "private" A345 is probably more concerned about satisfying their own personal safety concerns than optimal operating economics. Is it "immoral" and/or "shortsighted" to appeal to such fears/concerns when marketing an aircraft? Interesting.
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TinkerBelle
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RE: The Ongoing Two Engines Vs. Four Debate

Sat Feb 10, 2007 7:04 pm

Kinda stupid that they're still talking about safety being better on a four-engined aircraft than a two. Way to go Leahy, continue stuffing your foot in your mouth. Sometimes I wonder how the hell this guy is such a darn good salesman with the kind of stuff that comes out of his mouth. Will be interesting to see him change his stance when trying to sell the A350.
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RE: The Ongoing Two Engines Vs. Four Debate

Sat Feb 10, 2007 7:16 pm

There was an interesting article in todays paper here about this. NZ is now pleased that its investment in 2 engine long haul aircraft (B777 and B787s) will pay off with Boeings ETOPS range. I feel safe flying in a twin engine as I do flying in a quad.

Of topic, but has anything else happened in relation to a post on here a while ago about VS looking at changing its 4 engine slogan?
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leelaw
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RE: The Ongoing Two Engines Vs. Four Debate

Sat Feb 10, 2007 7:21 pm

Quoting 777ER (Reply 2):
but has anything else happened in relation to a post on here a while ago about VS looking at changing its 4 engine slogan?

See: "Virgin Atlantic removes Airbus slogan"
http://blog.seattlepi.nwsource.com/aerospace/archives/110431.asp



See also: Virgin Atlantic Might Want To Rethink Its Slogan (by Leelaw Jan 10 2007 in Civil Aviation)

[Edited 2007-02-10 11:26:05]
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RE: The Ongoing Two Engines Vs. Four Debate

Sat Feb 10, 2007 7:25 pm

Quoting TinkerBelle (Reply 1):
Kinda stupid that they're still talking about safety being better on a four-engined aircraft than a two.

I don't see the word "safety" in either the Leahy statement:

"Already doing sterling service on the world's longest airline routes, the Airbus A340-500 has exactly what a VIP customer wants -- a very large and attractive cabin, four-engined freedom for routings over the remotest regions, and the range to fly nonstop to the world,'' Airbus Chief Operating Officer John Leahy said in a statement.

Or the other quoted part of the release:

"Widebody VIP aircraft offer customers both a larger cabin and more range, allowing larger groups to fly even further nonstop in greater comfort and style. And for customers that select a four-engined A340 or A380, there are added benefits. These include the ability to continue to their destination after an engine failure, better take-off performance in hot and high conditions, and the freedom to overfly remote areas free from extended range twin-engine operations (ETOPS) limitations."

I do see the reporter extrapolating, but I don't see how you can blame Mr. Leahy for that.

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philb
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RE: The Ongoing Two Engines Vs. Four Debate

Sat Feb 10, 2007 7:31 pm

TinkerBelle,

Have you thought about spending 180 minutes with 300 odd other people on a single engined aircraft with possibly just 1 diversion airport in range - and that being in Siberia or a Pacific island where there is a statistical chance that the runway could be blocked by another incident before you get there?

Twins have proved themselves to be far more reliable than most people thought they would be when ETOPS was launched but if you look at the routes on which the A350/B787 are likely to be used they are not the routes where 180 minutes is an absolute requirement to divert to any airport rather than the worst option. That is why they will be used on the Atlantic, Indian Ocean and over parts of Africa and Asia with multiple diversion points but not on the ultra long haul routes with few alternates.

Leahy is a good salesman because he sells great products on their merits.

Use your acumen as a Financial Analyst to analyse Leahy's statements rather than your anti Airbus prejudice and you would realise that in aviation multiple redundancy is a requirement in many instances, not a luxury.

On the basis of your argument no airliner would have more than the minimum systems required to make it fly - something the industry went away from for very good reasons over 70 years ago starting with the B247 and the DC3.
 
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RE: The Ongoing Two Engines Vs. Four Debate

Sat Feb 10, 2007 7:33 pm

Quoting Mariner (Reply 4):
"Already doing sterling service on the world's longest airline routes, the Airbus A340-500 has exactly what a VIP customer wants -- a very large and attractive cabin, four-engined freedom for routings over the remotest regions, and the range to fly nonstop to the world,

"And the extra bonus of paying for more fuel due to our awesome gas loving A340, what else could you want?"

Quoting Leelaw (Reply 3):

Thanks
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RE: The Ongoing Two Engines Vs. Four Debate

Sat Feb 10, 2007 7:33 pm

Quoting Mariner (Reply 4):
I do see the reporter extrapolating, but I don't see how you can blame Mr. Leahy for that.

Indeed, however, I think Mr. Wallace would argue that Mr. Leahy's statements are chock full of "code words/phrases" which raise the issue of safety.
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RE: The Ongoing Two Engines Vs. Four Debate

Sat Feb 10, 2007 7:35 pm

Quoting 777ER (Reply 6):
"And the extra bonus of paying for more fuel due to our awesome gas loving A340, what else could you want?"

I don't see where Mr. Leahy said that either, but clearly some customers are happy to do it.

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RichardPrice
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RE: The Ongoing Two Engines Vs. Four Debate

Sat Feb 10, 2007 7:38 pm

Quoting 777ER (Reply 6):
"And the extra bonus of paying for more fuel due to our awesome gas loving A340, what else could you want?"

"Or would you rather pay the extra money to gain and then maintain an ETOPS rating with a single aircraft?"

Remember that ETOPS is still required by many aviation authorities around the world for VIP aircraft, and ETOPS ratings are not automatic or easy to keep, especially for an ultra small fleet.

While ETOPS still rules, a four engined aircraft for this sort of VVIP usage certainly has more merit than a twin, it can be argued.

[Edited 2007-02-10 11:39:00]
 
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RE: The Ongoing Two Engines Vs. Four Debate

Sat Feb 10, 2007 7:42 pm

Quoting 777ER (Reply 6):
"And the extra bonus of paying for more fuel due to our awesome gas loving A340, what else could you want?"

I presume you are banning flights by all 747s in favour of 340s? It seems a logical extension of this thought.
 
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RE: The Ongoing Two Engines Vs. Four Debate

Sat Feb 10, 2007 7:46 pm

I think the never dying 2 vs 4 discussion is becoming more telling about the ones that continue to bring it up then about the issue itself.


1972, Airbus A300, the first big twin, pioneering long overwater flights.
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RE: The Ongoing Two Engines Vs. Four Debate

Sat Feb 10, 2007 7:50 pm

Quoting Leelaw (Reply 7):
I think Mr. Wallace would argue that Mr. Leahy's statements are chock full of "code words/phrases" which raise the issue of safety.

He can argue what he likes, but I don't know the code - whatever it is, if there is one - so I still fail to see why people dump on Mr. Leahy for what he didn't say.

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TinkerBelle
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RE: The Ongoing Two Engines Vs. Four Debate

Sat Feb 10, 2007 7:52 pm

Quoting Philb (Reply 5):
if you look at the routes on which the A350/B787 are likely to be used they are not the routes where 180 minutes is an absolute requirement to divert to any airport rather than the worst option.

I wouldn't be too sure about that and 'likely' is the key word here.

Quoting Philb (Reply 5):
Use your acumen as a Financial Analyst to analyze Leahy's statements rather than your anti Airbus prejudice

Anti Airbus prejudice??? That's a new title for me I guess but I'm not prejudiced towards airbus. Airbus offers a superb product and what I have against them is their choice officials because most of them utter things only to eat their words later, especially Leahy. You can read all my previous posts and nothing indicates I'm a prejudiced towards Airbus.

Quoting Mariner (Reply 4):
I don't see the word "safety" in either the Leahy statement:

You're right, he didn't but you know very well what he means.  wink 
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RE: The Ongoing Two Engines Vs. Four Debate

Sat Feb 10, 2007 7:55 pm

Quoting TinkerBelle (Reply 13):
You're right, he didn't but you know very well what he means.   

Sorry, I don't know "what he meant" - beyond what he said.

And what he said seems entirely reasonable to me.

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RE: The Ongoing Two Engines Vs. Four Debate

Sat Feb 10, 2007 8:23 pm

Hmmm, is Leahy now saying that his A-330 is less safe than the A-340?  praise   scratchchin 

Isn't the A-330 currently Airbus's best selling WB?  duck 
 
OldAeroGuy
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RE: The Ongoing Two Engines Vs. Four Debate

Sat Feb 10, 2007 8:44 pm

Quoting Philb (Reply 5):
but if you look at the routes on which the A350/B787 are likely to be used they are not the routes where 180 minutes is an absolute requirement to divert to any airport rather than the worst option. That is why they will be used on the Atlantic, Indian Ocean and over parts of Africa and Asia with multiple diversion points but not on the ultra long haul routes with few alternates.

What basis do you have for making this statement?

I think that you will see versions of the A350/777/787 used on all airline long range (over 4000 nm) including the ultra long hauls.
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RE: The Ongoing Two Engines Vs. Four Debate

Sat Feb 10, 2007 9:00 pm

The 146 was made famous for 4 smaller, very quiet, efficient engines. Uprate that concept to a larger long-haul aircraft. Any two engine design will always suffer for size ultimatly, not range, but size. I think there is still life in 4 engine designs yet. For a large long haul twin aircraft the engines have to be large, look at the GE90's. The equivalent 4 engine design need not be so large and there is the safety factor with two extra power plants.
 
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RE: The Ongoing Two Engines Vs. Four Debate

Sat Feb 10, 2007 9:10 pm

Quoting KC135TopBoom (Reply 15):
Hmmm, is Leahy now saying that his A-330 is less safe than the A-340?

No.
Pls highlight the word safety out of his quoted sentence.....

The feeling of safety is not something that you can rationalize with. (Thats why is a feeling and not a logical resumption) .
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RE: The Ongoing Two Engines Vs. Four Debate

Sat Feb 10, 2007 9:39 pm

Quoting 777ER (Reply 2):
There was an interesting article in todays paper here about this. NZ is now pleased that its investment in 2 engine long haul aircraft (B777 and B787s) will pay off with Boeings ETOPS range. I feel safe flying in a twin engine as I do flying in a quad.

With Air NZ in my view it was an issue of "affordable" safety, which is what ETOPS goes back to, an ETOPS twin is not safer than quad, its just been shown to be "statistically safe".

Statistics is based upon probabilities, the chance of a double engine failure on a twin can be as probable as winning the lotto, just about every week someone seems to win lotto.

I have not seen a single statement from anyone to say a 330/767/777 is safer than a 340, just the 340 provides a higher degree of safety which some people are happier with a "statistically safe" twin engine platform.

And for the rich, why not, if you can afford it, go for a trijet like a Falcon 900 or a quad like a Dc8, 707, 747, 340, 380, which is safer, not just "statistically safe".
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RE: The Ongoing Two Engines Vs. Four Debate

Sat Feb 10, 2007 10:24 pm

Quoting Zeke (Reply 19):
Statistics is based upon probabilities, the chance of a double engine failure on a twin can be as probable as winning the lotto, just about every week someone seems to win lotto.

The regulatory probability of a dual engine failure on an ETOPS twin for a diversion time of more than 180 min. is on the order of one such event in 10 billion flight hours (1 in 10,000,000,000).

http://dmses.dot.gov/docimages/p88/436040.pdf

Are the odds on your lotto that improbable? If so, the tickets sales required to have a winner must be very high.

[Edited 2007-02-10 14:28:21]
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RE: The Ongoing Two Engines Vs. Four Debate

Sat Feb 10, 2007 10:42 pm

Quoting Zeke (Reply 19):
I have not seen a single statement from anyone to say a 330/767/777 is safer than a 340, just the 340 provides a higher degree of safety which some people are happier with a "statistically safe" twin engine platform.

Those who claim a 4 engine jet is safer always base their argument on the long haul over water case. In which case there has never been a hull loss of an ETOPS twin.

On the other hand they ignore the enhanced takeoff performance of the ETOPs twin over a 4 engine jet, namely the ability to continue a takeoff and climb on only 50% of the installed thrust. In this case there have been a number of 4 engine jet hull loses with all aboard killed: namely EL AL at Amsterdam & E-3 birdstrike incident at Elmendorf and I'm sure there are others.

So I'll give you your statement: A ETOPS twin is safer than a 4 engine long haul jet
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RE: The Ongoing Two Engines Vs. Four Debate

Sat Feb 10, 2007 10:58 pm

Quoting ZANL188 (Reply 21):
ETOPS twin is safer than a 4 engine long haul jet

And I´m sure you will further explain this.

Why is a A330 safer then a A340?

I know a carrier maintaining their 4 engined aircraft to the same ETOPS standards as their 2 engined ones.. perhaps an interesting start for your justification (apart from the anecdotal, belly feeling one).
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RE: The Ongoing Two Engines Vs. Four Debate

Sat Feb 10, 2007 11:05 pm

Quoting OldAeroGuy (Reply 16):
What basis do you have for making this statement?

I think that you will see versions of the A350/777/787 used on all airline long range (over 4000 nm) including the ultra long hauls.

What basis do you have for your assertion?.

Look at the airlines which have ordered the two types so far. Look at the size of the various versions and the routes those airlines fly. Then go to http://gc.kls2.com/ and plot some of the ultra long haul routes tjhose airlines fly using the 120 and 180 minute rule delimiters on the page. (You don't have to rely on Great Circle calculations, you can plot dog legs/minimum time tracks using way points)

There are a some routes that can't be flown within the 180 minute rule. There are a great deal more that are outside the 120 minute rule and many between 120 and 180 minutes are sparse on choice of commercially acceptable diversion points which are a factor when allocating types to a route..
 
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RE: The Ongoing Two Engines Vs. Four Debate

Sat Feb 10, 2007 11:13 pm

Quoting ZANL188 (Reply 21):
So I'll give you your statement: A ETOPS twin is safer than a 4 engine long haul jet

Current fleet statistics indicate there is no significant safety difference between Twins and Quads for current generation aircraft.

http://www.boeing.com/news/techissues/pdf/statsum.pdf
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RE: The Ongoing Two Engines Vs. Four Debate

Sat Feb 10, 2007 11:18 pm

Quoting Keesje (Reply 22):
And I´m sure you will further explain this.

I'd be happy to. 4 engine jets are not required by regulation to survive a loss of 50% of installed engine thrust on takeoff & early climb, ETOPs twins are. As a result there has not been a hull loss of an ETOPs twin following loss of 50% of installed thrust on takeoff. There have been a number of 4 engine jet hull losses (with all aboard killed) in the same case.

On the other hand there has not been a ETOPs twin hull loss (let alone a fatality) following engine failure on a long haul over water flight.

Therefore when considering the entire flight envelope the ETOPS twin is arguably safer than a long haul 4 engine jet when considering loss of thrust/engine shutdown accidents.

Quoting ZANL188 (Reply 21):
Those who claim a 4 engine jet is safer always base their argument on the long haul over water case. In which case there has never been a hull loss of an ETOPS twin.

On the other hand they ignore the enhanced takeoff performance of the ETOPs twin over a 4 engine jet, namely the ability to continue a takeoff and climb on only 50% of the installed thrust. In this case there have been a number of 4 engine jet hull loses with all aboard killed: namely EL AL at Amsterdam & E-3 birdstrike incident at Elmendorf and I'm sure there are others.
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RE: The Ongoing Two Engines Vs. Four Debate

Sat Feb 10, 2007 11:24 pm

Quoting OldAeroGuy (Reply 24):
Current fleet statistics indicate there is no significant safety difference between Twins and Quads for current generation aircraft.

I'm sure your statistics are quite valid and I have no argument with them.

On the other hand you have offered no argument to counter the facts of the accident record where loss of 50% of installed thrust on takeoff is concerned.
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RE: The Ongoing Two Engines Vs. Four Debate

Sat Feb 10, 2007 11:25 pm

Let me just add to this colourful thread, that I would rather fly on a well-maintained twin, than a badly maintained quad.

The recent multiple engine change of an Asian carriers a/c in Germany (FRA?) recently due to poor maintenance (if any existed in the first place!) proves that today both Boeing & Airbus design & manufacture some amazing and extremely reliable aircraft - only for them to be run into the ground by shoddy maintenance by the airlines.

Give me a loved B767, B777, B747, or A330, A340 or A350/380 anytime - I don't care. Good pilots & good maintenance - that's what I care about!
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RichardPrice
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RE: The Ongoing Two Engines Vs. Four Debate

Sat Feb 10, 2007 11:31 pm

Quoting ZANL188 (Reply 25):

I'd be happy to. 4 engine jets are not required by regulation to survive a loss of 50% of installed engine thrust on takeoff & early climb, ETOPs twins are. As a result there has not been a hull loss of an ETOPs twin following loss of 50% of installed thrust on takeoff. There have been a number of 4 engine jet hull losses (with all aboard killed) in the same case.

Im pretty sure thats not just a requirement of ETOPs, its a requirement of opearting any twin, ETOPs or not.

The El Al crash was not the result of a simple engine failing, but one being lost off the wing entirely and one being pushed far out of aerodynamical normality, resulting in an airframe with drastically altered handling characteristics, not just a loss of thrust.
 
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RE: The Ongoing Two Engines Vs. Four Debate

Sat Feb 10, 2007 11:34 pm

Quoting Philb (Reply 23):
There are a some routes that can't be flown within the 180 minute rule.

First of all, the 180 min ETOPS limitation is a thing of the past. The whole world will be opening up to ETOPS beyond 180/207.

http://dmses.dot.gov/docimages/p88/436040.pdf

Secondly, I think you're judging the situation too soon. The advent of ultra long range Twins is too recent. As more of them become available, I think you'll see them supplanting the ultra long range Quads. As evidence, consider the 772LR has now sold more frames than the A345 (40 vs 32), despite the fact that the A345 has been on the market longer.
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RE: The Ongoing Two Engines Vs. Four Debate

Sat Feb 10, 2007 11:44 pm

Quoting OldAeroGuy (Reply 29):
First of all, the 180 min ETOPS limitation is a thing of the past. The whole world will be opening up to ETOPS beyond 180/207.

I will again reiterate the point I put forward earlier -

This thread is based on something Leahy said after the sale of a VVIP quad, and its also based on something people are inferring from that (ie quads are safer).

We are not talking about airline service restrictions here, we are talking about ultra small fleets of aircraft, which in most cases can not sustain an ETOPS rating certification because its too much money. ETOPS ratings are not free, and not handed out like candy.

In this case, its probably cheaper to go and buy a quad to begin with, eat the extra per mission fuel costs because theres lower maintenance costs involved. Theres no standard to have to maintain the aircraft at to fly those certain routes.

ETOPS operations over the past 25 years have proven twins to be as reliable when maintained to a certain standard (ie the ETOPS certification minimum standard), but is it cost and time effective to spend the money ETOPS rating your VVIP aircraft, of which you may only have one or two? From what Ive read, no, unless you can operate the VVIP aircraft as part of a national airline.
 
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RE: The Ongoing Two Engines Vs. Four Debate

Sat Feb 10, 2007 11:50 pm

Quoting RichardPrice (Reply 28):
The El Al crash was not the result of a simple engine failing, but one being lost off the wing entirely and one being pushed far out of aerodynamical normality, resulting in an airframe with drastically altered handling characteristics, not just a loss of thrust.

Irregardless of the aerodynamic condition of this aircraft, following the loss of thrust from two engines it would not have been able to climb away and was going to crash. The only question was where.
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philb
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RE: The Ongoing Two Engines Vs. Four Debate

Sun Feb 11, 2007 12:18 am

Quoting RichardPrice (Reply 30):
but is it cost and time effective to spend the money ETOPS rating your VVIP aircraft, of which you may only have one or two? From what Ive read, no, unless you can operate the VVIP aircraft as part of a national airline.

The point is equally valid for many airlines, more so once the 180/207 minute rule is replaced by what in effect will be a fly anywhere on a twin rule - but subject to far greater stringency in training, route planning, operational systems and on board equipment.

Of course the crunch will be when a long range twin from a high profile airline doesn't make an alternate where a tri jet or a quad certainly would have. The publicity will equate to "would you now buy a ticket to fly more than 3 hours on a single engined 300 seater?" Whilst this argument has been around for many years and, thankfully, hasn't become a reality, the statistical fact is that one day it will happen with consequences that cannot be foreseen.

Quoting ZANL188 (Reply 31):
Irregardless of the aerodynamic condition of this aircraft, following the loss of thrust from two engines it would not have been able to climb away and was going to crash. The only question was where.

That's very difficult to prove. Had the engine been torn off "clean" the aircraft should have been able to make a return to land. Had both engines been lost without the massive damage to the flying surfaces, according to Boeing, a 747 should be able to remain airborne and make a landing.

Quoting OldAeroGuy (Reply 29):
As evidence, consider the 772LR has now sold more frames than the A345 (40 vs 32), despite the fact that the A345 has been on the market longer.

Both aircraft are very specialist compared to the other models in the range and the discrepancy in the numbers sold is as much to do with fleet commonality as number of engines..
 
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RE: The Ongoing Two Engines Vs. Four Debate

Sun Feb 11, 2007 12:27 am

Another statistic to remember, is that when you have 4 engines, you are twice as likely to suffer an engine failure than a 2 engine aircraft is. In most cases, unless you are BA, this requires a diversion to the nearest suitable airfield. I don't have any stats on this, but I presume statistically anyway, a 4 engine plane is more likely to have to divert ... albeit an extremely small probability.


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RE: The Ongoing Two Engines Vs. Four Debate

Sun Feb 11, 2007 12:36 am

Quoting TinkerBelle (Reply 1):
Sometimes I wonder how the hell this guy is such a darn good salesman with the kind of stuff that comes out of his mouth. Will be interesting to see him change his stance when trying to sell the A350.

Becuse this is what salesmen do, they talk s**t. Say you are buying a used car, a late maodel of the previous generation model. Salesman will tell you haow reliable it is, how much the facelift have improved the car, blah, blah, blah. But then you change your mind, you might like a new model car, fresh from teh factory, to your prefrences. Then "Oh the new car is much improved, more equipment, better dynamics, mopre space, more refined" Makes the old one look like a heap of junk. Then if you say you are considering another type of car....."Oh thats not a good, its too common, equipment is not as good, they fall apart, etc" Doesnt matter if its true or not. Its all about the spin.

Quoting Philb (Reply 5):

Leahy is a good salesman because he sells great products on their merits.

Any one can sell a "good product on its merits". Good salesmen sell inferior products in large quantities. The fact that any 340's are currently being ordered is a testement to Leahy's sales abilities. Im not saying the 340 is bad, but its just not as good as the 777.

Quoting 777ER (Reply 6):
"And the extra bonus of paying for more fuel due to our awesome gas loving A340, what else could you want?"

Well to be fair, if you are in the position to buy a VIP A340 you wont much care about a small difference in fuel costs over a T7. Also you are much more likely to get yor 340 long before your 777. Also there would be psychological advantages to having 4 engines and such a long fuselage.

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RE: The Ongoing Two Engines Vs. Four Debate

Sun Feb 11, 2007 12:40 am

Philb my question to you then would be why are both OEM's making new generation twin engine a/c for long haul travel without a caveat that they not be used overwater? If it is a given that there will eventually be a crash of a twin because it did not have the capability of a 4 engine a/c one would think that those in management positions of the manufacturers and airlines would also know and see this inevitablity, hence they either not build or buy such products.
 
zanl188
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RE: The Ongoing Two Engines Vs. Four Debate

Sun Feb 11, 2007 12:47 am

Quoting Philb (Reply 32):
That's very difficult to prove. Had the engine been torn off "clean" the aircraft should have been able to make a return to land. Had both engines been lost without the massive damage to the flying surfaces, according to Boeing, a 747 should be able to remain airborne and make a landing.

Not hard to prove at all. Ask any four engine jet driver what he thinks of his chances of successfully recovering his aircraft after losing two engines on the same side, below 7000ft, and at MTOW.

Better yet ask an ETOPS twin driver what he thinks of his chances after losing all power on one wing (all else being the same).

There be your proof.

Where's PhilSquares when we need him  

[Edited 2007-02-10 16:49:12]
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zeke
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RE: The Ongoing Two Engines Vs. Four Debate

Sun Feb 11, 2007 12:52 am

Quoting OldAeroGuy (Reply 20):

Are the odds on your lotto that improbable? If so, the tickets sales required to have a winner must be very high.

Welcome to China.

Quoting ZANL188 (Reply 21):
On the other hand they ignore the enhanced takeoff performance of the ETOPs twin over a 4 engine jet, namely the ability to continue a takeoff and climb on only 50% of the installed thrust.

That is actually false, tri jets and quads have a higher/better certified takeoff gradient/performance than a twin. FYI a twin commercial airliner cannot commence a takeoff on 1 engine, it can only continue a takeoff once at sufficient speed. A tri jet or quad can commence a takeoff roll with one engine inoperative when on a maintenance ferry flight etc.

Quoting ZANL188 (Reply 25):
I'd be happy to. 4 engine jets are not required by regulation to survive a loss of 50% of installed engine thrust on takeoff & early climb, ETOPs twins are. As a result there has not been a hull loss of an ETOPs twin following loss of 50% of installed thrust on takeoff. There have been a number of 4 engine jet hull losses (with all aboard killed) in the same case.

ETOPS has nothing to do with takeoff performance (with the exception is looking at a departure alternate).

A loss of an engine on quad gives you better certified climb performance than a twin with no reduction to the systems, a loss of two engines on a quad gives you better climb performance than a twin with a double engine failure, with only mild system changes.

FYI a 340-600 can climb on 2 engines at MTOW, we can even maintain altitude with 3 engines out at a reduced weight. I have not see the 380 charts for that case, I would suggest it will also be able to do it as well.

Quoting ZANL188 (Reply 31):
Irregardless of the aerodynamic condition of this aircraft, following the loss of thrust from two engines it would not have been able to climb away and was going to crash. The only question was where.

FYI the El Al case you are talking about did not happen on takeoff, it happened at about 6000', it was not the loss of engine thrust, as far as I am aware both the engines that departed the aircraft were functioning at the time. They had the separation of two engines from the same wing due to a fault in the engine pylon. This was not the last time for that to happen to a 747.

The crash was not for a lack of thrust, it was for a lack of controllability, bit like the Lauda Air 767 crash.

Also trying to compare reliability based upon the number of engines alone it ridiculous, if I were to compare the 707 to 777, the 777 would be better, compare the 737-100 to A340, 340 would be better, if I were to look at a 737-100 to 707, I would still go 707.

As for your E3 case, no aircraft is certified for takeoff into a flock of birds, and a lot of military aircraft do not meet civil takeoff requirements due to all the extra bits they have hanging off them, and the practice of taking off at weights about what a civil version of the same aircraft would, and using "military thrust" settings. In the cold war, jets like the Vulcan and B52 would keep going even if they could not start an engine.

Flocks of birds have taken down single engine, twin engine, tri jets, and quads before, and will do so again in the future.

The technology available today is "statistically safe", the risk level in a modern quad is still less than modern twin. Quads still have more redundancy.

Quoting Bond007 (Reply 33):
In most cases, unless you are BA, this requires a diversion to the nearest suitable airfield.

Nope it never has, it depends on the situation, hence the reason why the FAA dropped its case.

Having more engines does not mean you have a higher chance of a failure, the probability of having a failure depends on the age and history of the engine, and any known problems with the design. Failures due to accessories and metallurgical failure can be predicted accurately, and increase with the cycles, and the stress of the cycles.
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philb
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RE: The Ongoing Two Engines Vs. Four Debate

Sun Feb 11, 2007 12:54 am

Quoting Par13del (Reply 35):
Philb my question to you then would be why are both OEM's making new generation twin engine a/c for long haul travel without a caveat that they not be used overwater? If it is a given that there will eventually be a crash of a twin because it did not have the capability of a 4 engine a/c one would think that those in management positions of the manufacturers and airlines would also know and see this inevitablity, hence they either not build or buy such products.

My question to you is why does anyone fly, or drive or ride in a car? It's inevitable that there will be fatal accidents, so why travel at all?
.
Life is a balance of risk against need and the achievable. There are plenty of overwater and over sparsely inhabited area routes well suited to twins. The problem comes when the manufacturers are pushed by the airlines to push the regulators to overstretch the envelope.

Quoting BrianDromey (Reply 34):
Becuse this is what salesmen do, they talk s**t.



Quoting BrianDromey (Reply 34):
Any one can sell a "good product on its merits". Good salesmen sell inferior products in large quantities

Coming from someone with your undoubted miniscule experience of sales, your comments are highly insulting. I've known many very honest and highly successful salesmen in many industries around the world in the 42 years since I started in business. I've also been a succesful salesman at one time myself.

I'm sure you'd be pleased to have someone state here that all students are idle loafers wasting their time for three or four years because they would rather produce a essays and attend the odd lecture whilst avoiding real work and real training.

Because I have had many years of dealing with real students as a parent, part time lecturer and employer I know the above to be as stupid and as false as your ridiculous assertion.
 
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zeke
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RE: The Ongoing Two Engines Vs. Four Debate

Sun Feb 11, 2007 12:57 am

Quoting ZANL188 (Reply 36):
Not hard to prove at all. Ask any four engine jet driver what he thinks of his chances of successfully recovering his aircraft after losing two engines on the same side, below 7000ft, and at MTOW.

Not a problem on a 340, loss of two engines at MTOW, I can maintain height at lighter weights with only one engine.

With a 330/340, at 7000' would be enough height to do a glide approach in either a 330 or 340 after takeoff with no engine operating.
We are addicted to our thoughts. We cannot change anything if we cannot change our thinking – Santosh Kalwar
 
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par13del
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RE: The Ongoing Two Engines Vs. Four Debate

Sun Feb 11, 2007 1:07 am

I agree with your reply Philib, I asked the question based on your premise that after the crash, people would not want to fly twin's overwater.

Since the vast majority - absolute numbers - of airlines are national or have heavy political involvement, I may quibble with the notion that the airlines are pushing the manufacturers to push the politicians, I would go with the idea that the airlines are pushing the manufacturers to provide the policitians with "papers" to justify the decisions that they want to make.
 
zanl188
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RE: The Ongoing Two Engines Vs. Four Debate

Sun Feb 11, 2007 1:11 am

Quoting Zeke (Reply 37):
That is actually false, tri jets and quads have a higher/better certified takeoff gradient/performance than a twin. FYI a twin commercial airliner cannot commence a takeoff on 1 engine, it can only continue a takeoff once at sufficient speed. A tri jet or quad can commence a takeoff roll with one engine inoperative when on a maintenance ferry flight etc.

If you will read carefully you'll note that I'm not counting the number of engines nor have I stated that a twin can start a takeoff on one engine.

What I am saying is that an ETOPS twin is certified to continue takeoff and climb after losing 50% of it's installed thrust. A four engine jet is not.

Quoting Zeke (Reply 37):
ETOPS has nothing to do with takeoff performance (with the exception is looking at a departure alternate).

I have made no claim that it does. Again read carefully.

Quoting Zeke (Reply 37):
The crash was not for a lack of thrust, it was for a lack of controllability

Are you saying that it would have been able to maintain altitude or climb after losing two engines on one side at low altitude with takeoff weight and fuel, and that said loss of all thrust on one side had no impact on controllability issues? Please think again....

Quoting Zeke (Reply 37):
As for your E3 case, no aircraft is certified for takeoff into a flock of birds, and a lot of military aircraft do not meet civil takeoff requirements due to all the extra bits they have hanging off them, and the practice of taking off at weights about what a civil version of the same aircraft would, and using "military thrust" settings.

I haven't claimed that any aircraft is certified to fly into a flock of birds, please quote me correctly. If being a military aircraft is issue , fine put a 707 in the same scenario. If a 707 loses all thrust (to birds) on one side at V1 it will not climb away. An ETOPs twin in the same situation will. It's all in how they are certified and designed.
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philb
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RE: The Ongoing Two Engines Vs. Four Debate

Sun Feb 11, 2007 1:15 am

Par13del,

How much people would be influenced by such an accident has been the topic of many aviation think tank discussions over many years.

As time has gone on and twins have proved their reliability the sting would seem to have been taken out of the debate but a major accident to a twin, which would have been avoided in a tri or quad, especially if it happened on an ETOPS sector beyond the current limits in the early days of operation, would cause a furore that wouldn't be restricted to aviation circles and those immediately involved.

I like the fine distinction you draw in your second para - very perceptive!
 
zanl188
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RE: The Ongoing Two Engines Vs. Four Debate

Sun Feb 11, 2007 1:22 am

Quoting Zeke (Reply 39):
Not a problem on a 340, loss of two engines at MTOW, I can maintain height at lighter weights with only one engine.

Huh? Which is it MTOW or a "lighter weight"? Your A340 is not certified nor designed to lose all engines on one wing at takeoff and survive.

Quoting Zeke (Reply 39):
With a 330/340, at 7000' would be enough height to do a glide approach in either a 330 or 340 after takeoff with no engine operating.

Good luck, since this a takeoff scenario we are discussing the runway you are trying to reach is behind you and getting further away as you attempt to react. You will lose significant altitude doing your 180 and trip back to the runway not to mention what you'll lose on approach.

Sorry, give me an ETOPs twin with a 50% loss of thrust in the same scenario any day! it's designed and certified to do this, your A340 is not.
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philb
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RE: The Ongoing Two Engines Vs. Four Debate

Sun Feb 11, 2007 1:24 am

Quoting ZANL188 (Reply 41):
Are you saying that it would have been able to maintain altitude or climb after losing two engines on one side at low altitude with takeoff weight and fuel, and that said loss of all thrust on one side had no impact on controllability issues? Please think again....

I don't think he's saying that at all. The controlability of the aircraft in that accident was compromised beyond retrievability due to major flying surfaces and systems being destroyed. Had the engine come off "clean", at that height with the thrust available and the proximity of the field, the accident would, in all probability, have been an incident, no more.

The AA DC10 accident at ORD in 1979 was a similar case. Had the engine not destroyed leading edge slats and taken out some hydraulics, it was proved on simulator by AA and MDD, that the aircraft could have been flown out and been able to dump fuel and return.

[Edited 2007-02-10 17:26:14]
 
zanl188
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RE: The Ongoing Two Engines Vs. Four Debate

Sun Feb 11, 2007 1:27 am

Quoting Philb (Reply 44):
Had the engine come off "clean", at that height with the thrust available and the proximity of the field, the accident would, in all probability, have been an incident, no more.

But it didn't come off clean. It took out the other engine. Once that happened the only thing in doubt was the location of the accident.
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RichardPrice
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RE: The Ongoing Two Engines Vs. Four Debate

Sun Feb 11, 2007 1:31 am

Quoting ZANL188 (Reply 41):

Are you saying that it would have been able to maintain altitude or climb after losing two engines on one side at low altitude with takeoff weight and fuel, and that said loss of all thrust on one side had no impact on controllability issues? Please think again....

A two engines out on the same wing situation produces a predictable controllability change, while the El Al crash also sustained wing and aerodynamic changes through the loss of those wings, not to mention the loss of weight from one wing.

One results in a trim situation for the pilot, the other results in an unknown and potentially drastrically changed performance envelope for the aircraft.

One is trainable for, the other is essentially left to prayer and skill of the pilot at the controls at the time.

Quoting ZANL188 (Reply 41):
What I am saying is that an ETOPS twin is certified to continue takeoff and climb after losing 50% of it's installed thrust. A four engine jet is not.

Thats a little disingenuous, since theres no certification at all of that type for the quad so its hardly an arguable point.

You would be better arguing actual capability than arguing whether or not a non existing certification has a particular performance point as a requirement.
 
philb
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RE: The Ongoing Two Engines Vs. Four Debate

Sun Feb 11, 2007 1:31 am

Quoting ZANL188 (Reply 45):
But it didn't come off clean. It took out the other engine. Once that happened the only thing in doubt was the location of the accident.

So, in your view, loss of two engines on one wing at low altitude means an inevitable crash?
 
zanl188
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RE: The Ongoing Two Engines Vs. Four Debate

Sun Feb 11, 2007 1:44 am

Quoting RichardPrice (Reply 46):
Thats a little disingenuous, since theres no certification at all of that type for the quad so its hardly an arguable point.

Sure it's an arguable point. The nature of the design and certification can certainly make one type of aircraft safer than another, it's done all the time. The fact is that an ETOPS twin is designed and certified to survive the loss of all thrust on one wing at takeoff and a 4 engine jet is not.

A byproduct of this fact is that an ETOPS twin has more thrust available (per lb of gross weight) for escape manuevers than an otherwise similiar 4 engine jet.

Quoting Philb (Reply 47):
So, in your view, loss of two engines on one wing at low altitude means an inevitable crash?

So, in my view, an ETOPs twin is designed and certified to lose all thrust on one wing at takeoff or initial climb and survive. A 4 engine jet is not.
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Dougloid
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RE: The Ongoing Two Engines Vs. Four Debate

Sun Feb 11, 2007 1:50 am

Quoting Keesje (Reply 11):
I think the never dying 2 vs 4 discussion is becoming more telling about the ones that continue to bring it up then about the issue itself.

Yes....let us put this to rest, starting with John Leahy.

His mouth is an ever flowing wellspring of discontent and disinformation.
If you believe in coincidence, you haven't looked close enough-Joe Leaphorn

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