Moderators: jsumali2, richierich, ua900, PanAm_DC10, hOMSaR

 
BoomBoom
Posts: 2459
Joined: Fri Nov 04, 2005 2:26 am

RE: The Ongoing Two Engines Vs. Four Debate

Sun Feb 11, 2007 2:06 am

Quoting BrianDromey (Reply 34):

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.

Unless you're a "limousine liberal", who cares more about being a good citizen of the planet, by not wasting fuel.
Our eyes are open, our eyes are open--wide, wide, wide...
 
bond007
Posts: 4428
Joined: Mon Mar 14, 2005 2:07 am

RE: The Ongoing Two Engines Vs. Four Debate

Sun Feb 11, 2007 2:18 am

Quoting Zeke (Reply 37):
Nope it never has, it depends on the situation, hence the reason why the FAA dropped its case.

Not sure what you mean by "nope, it never has". Sure a single engine failure on a 4-engine aircraft has meant a diversion or return - it happened only recently (I'll look up details if you'd like), and I'm sure on other occasions. As you say - it depends on the situation.

Quoting Zeke (Reply 37):
Having more engines does not mean you have a higher chance of a failure,

It sure does. Twice as many engines = double the chance of a single engine failing ... however small that might be.

Quoting Zeke (Reply 37):
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.

...this is true for an aircraft with any number of engines.

Quoting Zeke (Reply 37):
the probability of having a failure depends on the age and history of the engine, and any known problems with the design.

...and number of engines (if you mean any single engine failing).

Hey, I'm not advocating 2 is safer than 4 or vice versa, just that with 4 you ARE more likely to have a single engine fail. If flying with 3 engines has no consequences to the flight, then the point is moot - if flying with 3 engines means diversion or return - then this is more likely with a 4 engine aircraft.




Jimbo
I'd rather be on the ground wishing I was in the air, than in the air wishing I was on the ground!
 
sstsomeday
Posts: 821
Joined: Thu Oct 26, 2006 2:32 pm

RE: The Ongoing Two Engines Vs. Four Debate

Sun Feb 11, 2007 2:53 am

Quoting Leelaw (Thread starter):
Is it "immoral" and/or "shortsighted" to appeal to such fears/concerns when marketing an aircraft? Interesting.

It's my observation that business is completely ruthless in it's desire to compete and kill the competition, and marketing is not exempt from that strategy. Any large company will advertise, spin and promote with whatever they can get away with in order to make the sale and not get caught being dishonest, especially if the statistics can be interpreted differently as "a matter of opinion."

Quoting Leelaw (Thread starter):
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...

Whether they are doing this blatantly or subliminally, it is ironic and disingenuous - since they are developing the 350 and sell the 330 NOW.

Quoting Mariner (Reply 4):
four-engined freedom for routings over the remotest regions

My understanding is, since ETOPS has recently been expanded, that there is now virtually no remote terrain or water routes that the 777 may not navigate over in a straight line that the 340 can.

However, to play devils advocate, I have noticed a number of rather dramatic compressor failures reported in the news and being discussed in these threads of late. I'm beginning to wonder if the statistical improbability of a double engine failure on a twin is as remote as we think it is.

Are compressors on long range twins (and their engines in general) built or maintained to a higher standard in order to retain the ETOPS certification?
I come in peace
 
User avatar
NWAROOSTER
Posts: 1379
Joined: Mon Feb 14, 2005 2:29 pm

RE: The Ongoing Two Engines Vs. Four Debate

Sun Feb 11, 2007 2:59 am

Four engines with be always be safer than two. Engine technology has improved to the point that the reliability of aircraft engine are almost perfect. However, there are outside sources that can cause engine failure such as a bird strike on takeoff. A twin engine aircraft that looses an engine on takeoff, especially one that has 100,000 pound thrust engines, would have a major asymmetry problem at rotation and have very strong yaw shift in the direction of the of the side which lost power. The pilot would have to correct this with the ruder to avoid a catastrophic loss of control of the aircraft as there would be little, if any altitude to deal with as a safety factor.
Also, a twin engine aircraft that has an engine failure over the ARTIC, could have a problem maintaining all its systems in a very harsh environment with no place to land, if that became necessary.
They are just going to have to build more fuel efficient four engine aircraft to maintain there continuance in the future.
Procrastination Is The Theft Of Time.......
 
okie73
Posts: 357
Joined: Sat Mar 18, 2006 11:09 pm

RE: The Ongoing Two Engines Vs. Four Debate

Sun Feb 11, 2007 3:06 am

Quoting Nwarooster (Reply 53):
A twin engine aircraft that looses an engine on takeoff, especially one that has 100,000 pound thrust engines, would have a major asymmetry problem at rotation and have very strong yaw shift in the direction of the of the side which lost power. The pilot would have to correct this with the ruder to avoid a catastrophic loss of control of the aircraft

actually, the only aircraft certified to operate with an engine that size is the 777, which has automatic yaw compensation. In the event of an engine failure, rudder is put in automatically.
 
User avatar
mariner
Posts: 19473
Joined: Fri Nov 23, 2001 7:29 am

RE: The Ongoing Two Engines Vs. Four Debate

Sun Feb 11, 2007 3:15 am

Quoting SSTsomeday (Reply 52):
My understanding is, since ETOPS has recently been expanded, that there is now virtually no remote terrain or water routes that the 777 may not navigate over in a straight line that the 340 can.

I still don't see that negates a thing Mr. Leahy said:

"...a very large and attractive cabin, four-engined freedom for routings over the remotest regions, and the range to fly nonstop to the world,''"

What in that statement is untrue? The A340 has four engines and it can fly to the remotest regions of the world.

He doesn't say that a twin jet can't fly to the remotet regions of the world. That is an extrapolation - but it isn't what he said.

???

mariner
aeternum nauta
 
redflyer
Posts: 3905
Joined: Thu Feb 24, 2005 3:30 am

RE: The Ongoing Two Engines Vs. Four Debate

Sun Feb 11, 2007 4:07 am

Quoting Leelaw (Thread starter):
Is it "immoral" and/or "shortsighted" to appeal to such fears/concerns when marketing an aircraft?

I wouldn't call it immoral, but definitely shortsighted since the rest of their future product line-up will consist of twins only (not counting the WhaleJet, which will require quad status because currently its MTOW bars use of twin engines since max thrust on engines aren't high enough yet).

**********

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



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

Mariner, you're a writer so you should know better than most that conveying a message often times entails what you do NOT say as much as what you do say (this is especially true in sales). No one here is divining tea leaves regarding Leahy's comments. Airbus had a marketing campaign in AW&ST back in 2003 that clearly conveyed the "safer" 4-engine A340 (the illustration of an A340 flying over stormy and shark-infested waters). That, coupled with Airbus' previous "4 engines 4 long haul" campaign leaves no doubt that a cornerstone of Airbus' marketing for its A340 entails the purported safety of 4 engines. So now Leahy comes along and spouts off about the benefits of 4 engines and all but says the plane is safer. No "extrapolation" is necessary. If it barks like a dog and smells like a dog, well then...

**********

Quoting Mariner (Reply 4):
"These include the ability to continue to their destination after an engine failure",

Yes, Leahy was correct in saying that the A340 has the ability to continue to its destination after an engine failure. But then, so does a twin. As others have pointed out, all aircraft -- quad or twin -- should divert to the nearest airport when an engine fails. But that doesn't mean they can't make it to their destination.

**********

Quoting Mariner (Reply 12):
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.

Not sure anyone has "dumped" on Leahy, but the fact remains that he is the kingpin of Airbus' marketing machine. He, more than anyone, has to choose his words carefully and, in that regard, there is often times as much weight given to what he does not say as much as what he does say. I'm sure he, like anyone in marketing, is cognizant of that fact.
A government big enough to take away a constitutionally guaranteed right is a government big enough to take away any guaranteed right. A government big enough to give you everything you need is a government big enough to take away everything you have.
 
zanl188
Posts: 3816
Joined: Sat Oct 21, 2006 9:05 pm

RE: The Ongoing Two Engines Vs. Four Debate

Sun Feb 11, 2007 4:11 am

Quoting Nwarooster (Reply 53):
Four engines with be always be safer than two.

IMHO Unless aviation authorities change the way aircraft are designed and certified this will never be true. If things continue as they are 4 engine aircraft will always have poorer takeoff and initial climb characteristics as opposed to a comparable ETOPs twin. Although this does not make a 4 engine jet "unsafe" it does make it less safe than a comparable ETOPs twin.
Legal considerations provided by: Dewey, Cheatum, and Howe
 
jbernie
Posts: 206
Joined: Wed Jan 10, 2007 10:09 am

RE: The Ongoing Two Engines Vs. Four Debate

Sun Feb 11, 2007 4:38 am

I prefer flying with FIVE engines....

My dad flew on a QF 742 or 743 back in the early 90s I believe which had a 5th engine strapped to one of the wings some how to transport it back to Sydney.
 
User avatar
mariner
Posts: 19473
Joined: Fri Nov 23, 2001 7:29 am

RE: The Ongoing Two Engines Vs. Four Debate

Sun Feb 11, 2007 4:47 am

Quoting RedFlyer (Reply 56):
Mariner, you're a writer

And as a writer I have a profound respect for the use of language. Mr. Leahy clearly chose his words very carefully - to celebrate a good sale - but is being criticsed for what he may have said in the past.

It is the journalist who is playing games with English here.

mariner
aeternum nauta
 
User avatar
zeke
Posts: 15767
Joined: Thu Dec 14, 2006 1:42 pm

RE: The Ongoing Two Engines Vs. Four Debate

Sun Feb 11, 2007 5:00 am

Quoting ZANL188 (Reply 41):
I have made no claim that it does. Again read carefully.

Well with respect your posts show a total lack of knowledge. "ETOPs twin with a 50% loss" is nothing to do with ETOPS, takeoff performance is purely based on then number of engines in FAR 25, yet you mention it in just about every sentence you talk about ETOPS. Why ?

As a person who has actually flown the 744, and currently flies the 330 and 340, I find your ability to dismiss my comments so easily very frustrating. When I say I can do a glide approach from 7000', I know I can because I have done it in the sim. The 330/340 is a very slippy aircraft, I would do over 20-25 nm from 7000' with no engines on departure (even the best part of 30 depending on the speed at 7000').

When I say I can have two engines fail on takeoff with the 340, again I know I can do it as I have done it in the sim, I am sure Phil has done similar in the 744. Even at MTOW I have done this, again please open your mind a little to people with actual experience on the types being discussed.

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....

Are you familiar with the report, or are you quoting some ramblings someone else wrote ?

They lost almost instantaneously 15000-20000 lb (the two complete engines) of mass off one wing, they had a large almost instant change to the cg rearwards with that loss of mass of two engine on one wing, a rearwards CG is not what one wants when you need a lot of rudder. A JAL 747 which also lost the complete engine and mount off the wing at ANC returned back to land at ANC.

Quoting ZANL188 (Reply 41):
An ETOPs twin in the same situation will. It's all in how they are certified and designed.

Hmm, please go an check all the facts, a number of twins have suffered a hull loss after birds strikes on takeoff. I remember a number of 737s have, in particular a KLM 734 about 10 years ago. Indian Airlines also wrote off an A300, and I seem to recall a number of corporate jets. All of which are certified to the same FAR 25 requirements.

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.

You would be better arguing actual capability than arguing whether or not a non existing certification has a particular performance point as a requirement.

 checkmark   checkmark   checkmark   checkmark   checkmark 

Quoting ZANL188 (Reply 48):
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.

That again is false, one of the reason our airline does not operate twins to Europe at the moment. Quads are better for escape maneuvers, have better climb gradients than a twin one engine, and carry more redundant systems.

With the loss of an engine on a twin, think about what you have left, not only in terms of thrust, but systems as well. An engine failure on a quad leaves us without and degradation to the aircraft systems.

Quoting Bond007 (Reply 51):
Sure a single engine failure on a 4-engine aircraft has meant a diversion or return - it happened only recently (I'll look up details if you'd like), and I'm sure on other occasions.

Please do, the FAR 121.565 does allow continuation by trijet and quads, "(b) If not more than one engine of an airplane that has three or more engines fails or its rotation is stopped, the pilot in command may proceed to an airport that he selects if, after considering the following, he decides that proceeding to that airport is as safe as landing at the nearest suitable airport:

(1) The nature of the malfunction and the possible mechanical difficulties that may occur if flight is continued.

(2) The altitude, weight, and usable fuel at the time of engine stoppage.

(3) The weather conditions en route and at possible landing points.

(4) The air traffic congestion.

(5) The kind of terrain.

(6) His familiarity with the airport to be used. "

Some company spec ops over ride this FAR.

Quoting Bond007 (Reply 51):
It sure does. Twice as many engines = double the chance of a single engine failing ... however small that might be.

Not according to engine manufacturers, they think the chances are actually lower on a quad as they engines are put under less stress than a twin, and generally do longer sectors hence less cycles. FYI BA actually put their 767 engines when tired from the 767 onto the 744 as the 744 does not work them as hard.

Quoting Okie73 (Reply 54):
actually, the only aircraft certified to operate with an engine that size is the 777, which has automatic yaw compensation. In the event of an engine failure, rudder is put in automatically.

A320/330/340/380 have similar, they will not roll onto their backs with an engine failure with no pilot control input.
“Don't be a show-off. Never be too proud to turn back. There are old pilots and bold pilots, but no old, bold pilots.” E. Hamilton Lee, 1949
 
User avatar
Ncfc99
Posts: 786
Joined: Tue May 31, 2005 2:42 am

RE: The Ongoing Two Engines Vs. Four Debate

Sun Feb 11, 2007 5:31 am

I have question for ZANL188. If an ETOPS twin lost 50% of its thrust by having an engine fall off and damage the wing, thus changing the controlability of the aircraft and the aerodynamics etc, would it still be able to climb and maintain height, return or divert to land safely? I think you are trying to compare an aircraft with engines missing to an aircraft with a shut down engine. No aircraft is certified to have an engine fall off the wing.
By the way, I flew from MAN-BNE on twins with EK and was quite nervous doing so, even after reading about twins on A.net.
 
Adria
Posts: 781
Joined: Wed Aug 09, 2000 7:53 am

RE: The Ongoing Two Engines Vs. Four Debate

Sun Feb 11, 2007 5:46 am

Quoting TinkerBelle (Reply 1):
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.

Well Boeing also criticized Airbus's fly-by-wire system by saying our pilots can override the computer yet they cannot do that on the 773ER any more.....
 
bond007
Posts: 4428
Joined: Mon Mar 14, 2005 2:07 am

RE: The Ongoing Two Engines Vs. Four Debate

Sun Feb 11, 2007 5:58 am

Quoting Zeke (Reply 60):
Please do, the FAR 121.565 does allow continuation by trijet and quads, "(b) If not more than one engine of an airplane that has three or more engines fails or its rotation is stopped, the pilot in command may proceed to an airport that he selects if, after considering the following, he decides that proceeding to that airport is as safe as landing at the nearest suitable airport:

Please, I'm not arguing FARs or whether it's safe to go ahead with 3 out of 4 engines - only that there are numerous occasions when either SOPs or other reasons (as you described), dictated (or recommended!), that the aircraft return or land at the nearest airport practicable.

Quoting Zeke (Reply 60):
Not according to engine manufacturers, they think the chances are actually lower on a quad as they engines are put under less stress than a twin, and generally do longer sectors hence less cycles.

Well, I would need to research that further (and will  Wink). I understand the engines maybe (or will be) under less stress, but they would have to be more than twice as unlikely to fail on a quad vs a twin to make the probability of a SINGLE engine failure less on a quad.

Jimbo
I'd rather be on the ground wishing I was in the air, than in the air wishing I was on the ground!
 
User avatar
zeke
Posts: 15767
Joined: Thu Dec 14, 2006 1:42 pm

RE: The Ongoing Two Engines Vs. Four Debate

Sun Feb 11, 2007 5:58 am

Quoting RedFlyer (Reply 56):
As others have pointed out, all aircraft -- quad or twin -- should divert to the nearest airport when an engine fails. But that doesn't mean they can't make it to their destination.

That is false see my comments regarding FAR Sec. 121.565 above.

Quoting ZANL188 (Reply 57):
If things continue as they are 4 engine aircraft will always have poorer takeoff and initial climb characteristics as opposed to a comparable ETOPs twin. Although this does not make a 4 engine jet "unsafe" it does make it less safe than a comparable ETOPs twin.

This is false, you really need to have a look at FAR 25.100 series , a summary is below.






































Segment 2 engine aircraft 4 engine aircraft
1st Positive rate 0.5%
2nd 2.4% 3.0%
3rd - -
4th 1.2% 1.7%
Approch climb (SE) 2.1% 2.4%
Landing climb (All) 3.2% 3.2%


These are the gross gradients, it is the demonstrated ratio expressed as a percentage of [Change of Height] / [Horizontal Distance Travelled]. For Instance: A climb gradient of 3.0% means an increase in altitude of 3' for every 100' forward travel. Net Gradient is the demonstrated gross climb gradient reduced by the decrement required by regulation, factors for net are 0.8% for 2 engine and 1.0% for 4 engine a/c.

The Take-Off Path as per FAR 25.111 is the accelerate-go path to 35' plus the flight path climb profile on a takeoff with the most critical engine failure occurring at V1 speed. The path extends from the standing start to a point in the take-off where a height of 1,500' above the take-off surface is reached [jet airport traffic circuit altitude], or to where transition from take-off to enroute configuration is complete, whichever is higher. For performance specifications, the FAA divides the climb into only 4 segments for the certification process:

1st Segment - Starts at 35' height (reference zero) and ends when gear retraction is complete.

2nd Segment - Starts when gear retraction is completed and ends at height of not less than 400' above the take-off surface (most operations use 800' to 1500') with the remaining engines at take-off thrust, the flaps at the take-off setting and the airplane flown at V2

3rd Segment - Starts at not less than 400' height (most operations use 800' or 1500' however) generally level accelerating and continues until flaps are retracted at takeoff thrust.

4th Segment - Starts at end of flap retraction and continues until acceleration to V2+50 knots where the thrust is reduced before the 5/10 minute maximum time limit for takeoff thrust is reached then back to maximum continuous thrust, extends to a gross height of 1500' AFE (above field elevation) or more, at a constant speed of V2+50 knots, green dot on the airbus.
“Don't be a show-off. Never be too proud to turn back. There are old pilots and bold pilots, but no old, bold pilots.” E. Hamilton Lee, 1949
 
User avatar
zeke
Posts: 15767
Joined: Thu Dec 14, 2006 1:42 pm

RE: The Ongoing Two Engines Vs. Four Debate

Sun Feb 11, 2007 6:15 am

Quoting Bond007 (Reply 63):
Well, I would need to research that further (and will Wink). I understand the engines maybe (or will be) under less stress, but they would have to be more than twice as unlikely to fail on a quad vs a twin to make the probability of a SINGLE engine failure less on a quad.

The manufacturers of the newer engines (normally the FADEC ones) can look at the probability of an engine failure across all operators for the type, generally engine parameters and health monitoring goes back to the manufacturer these days ontop of local company trend monitoring. All of our aircraft have flight and engine data taken off every week with our QARs on a 3.5" optical disk. They have a database of all engines out in service and can compare from the health monitoring which engines have been working harder than others, and which are showing anomalies and should be replaced/inspected.

If all engines were at the same factory pin setting for thrust, same software level, same oil, same fuel, and did the same takeoff derate/reduced thrust and other operating procedures, same cycles from the same airport ambient conditions, same maintenance programs, away from sea air and sand, no ice, stones, birds, golf balls, FOD etc, then I would agree with you. However in practice these are all minor variables which can effect engine life and the probability of failure.
“Don't be a show-off. Never be too proud to turn back. There are old pilots and bold pilots, but no old, bold pilots.” E. Hamilton Lee, 1949
 
bond007
Posts: 4428
Joined: Mon Mar 14, 2005 2:07 am

RE: The Ongoing Two Engines Vs. Four Debate

Sun Feb 11, 2007 6:16 am

Just for the record, regardless of FARS and SOPs:

"the 777 air turnback and diversion rate is about half that of the A340. For the 12-month period, the 777 rate was 0.29 turnbacks and diversions per 1000 revenue departures, and the A340 was 0.68"

Data: Boeing reliability, maintainability and testability group; Airbus Quarterly Service Report.


As I expected.

Jimbo
I'd rather be on the ground wishing I was in the air, than in the air wishing I was on the ground!
 
RichardPrice
Posts: 4474
Joined: Sat Apr 23, 2005 5:12 am

RE: The Ongoing Two Engines Vs. Four Debate

Sun Feb 11, 2007 6:26 am

Quoting Bond007 (Reply 66):

Out of interest, whats the rates between the 777 and the A330? Or can you point me to where I can get this information myself?
 
bond007
Posts: 4428
Joined: Mon Mar 14, 2005 2:07 am

RE: The Ongoing Two Engines Vs. Four Debate

Sun Feb 11, 2007 6:29 am

Quoting RichardPrice (Reply 67):
Out of interest, whats the rates between the 777 and the A330? Or can you point me to where I can get this information myself?

I can't find it again myself now! I did a Google search, and admittedly I think it was a Boeing article, but presumably they weren't lying about the numbers! It didn't mention A330 since it was a Boeing twin vs Airbus quad discussion - same as here!

Jimbo
I'd rather be on the ground wishing I was in the air, than in the air wishing I was on the ground!
 
RichardPrice
Posts: 4474
Joined: Sat Apr 23, 2005 5:12 am

RE: The Ongoing Two Engines Vs. Four Debate

Sun Feb 11, 2007 6:34 am

Quoting Bond007 (Reply 68):

I can't find it again myself now! I did a Google search, and admittedly I think it was a Boeing article, but presumably they weren't lying about the numbers! It didn't mention A330 since it was a Boeing twin vs Airbus quad discussion - same as here!

It would be interesting to find those figures independantly, as we all know marketing personel can be 'creative' with statistics to prove anything they want (every company is guilty of this, so dont assume anything by this comment)  Smile

I shall take a hunt around tomorrow.
 
User avatar
zeke
Posts: 15767
Joined: Thu Dec 14, 2006 1:42 pm

RE: The Ongoing Two Engines Vs. Four Debate

Sun Feb 11, 2007 6:46 am

Quoting Bond007 (Reply 68):
I can't find it again myself now! I did a Google search, and admittedly I think it was a Boeing article, but presumably they weren't lying about the numbers! It didn't mention A330 since it was a Boeing twin vs Airbus quad discussion - same as here!

Found the following http://avitop.com/cs/forums/2025/ShowThread.aspx

"Boeing also stated that B777 has lower turnback and diversion rate, but the rate includes those without mechanical faults (90% of all turnbacks and diversions), like sudden medical emergencies. The non-mechanical diversion and turnback rate is proportional to trip length, and A340 has average trip length of 10 hours per flight compared to 3 hours for B777, so A340 has higher non-mechanical fault diversion and turnback rate.

But the mechanical turnback and diversion rate for A340 is just 1/3 that of B777, because of reason stated above."
“Don't be a show-off. Never be too proud to turn back. There are old pilots and bold pilots, but no old, bold pilots.” E. Hamilton Lee, 1949
 
User avatar
keesje
Posts: 14159
Joined: Thu Apr 12, 2001 2:08 am

RE: The Ongoing Two Engines Vs. Four Debate

Sun Feb 11, 2007 6:59 am

Quoting ZANL188 (Reply 41):
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 60):
he decides that proceeding to that airport is as safe as landing at the nearest suitable airport:

(1) The nature of the malfunction and the possible mechanical difficulties that may occur if flight is continued

Zeke, thnx for your profesional insights. As I recall the ElAl crew was not fully aware of the condition of the aircraft after 2 engines shut down. I think they did not know they lost 2 & knew about the flap damage when they tried to lower them, moments before the crash as evidenced by the Air Traffic Control tape transcript .. http://aviation-safety.net/investiga...ion/cvr/transcripts/atc_ly1862.php

They probably would have made different choices (high speed landing) if they had known.

(the CVR recording, WARNING: Disturbing ..http://home.wanadoo.nl/lars.dejonge/Bijlmerramp.mp3 )
"Never mistake motion for action." Ernest Hemingway
 
bond007
Posts: 4428
Joined: Mon Mar 14, 2005 2:07 am

RE: The Ongoing Two Engines Vs. Four Debate

Sun Feb 11, 2007 7:01 am

Quoting Zeke (Reply 71):
"Boeing also stated that B777 has lower turnback and diversion rate, but the rate includes those without mechanical faults (90% of all turnbacks and diversions), like sudden medical emergencies. The non-mechanical diversion and turnback rate is proportional to trip length, and A340 has average trip length of 10 hours per flight compared to 3 hours for B777, so A340 has higher non-mechanical fault diversion and turnback rate.

But the mechanical turnback and diversion rate for A340 is just 1/3 that of B777, because of reason stated above."

Well, highly dubious interpretation there, and both the linked documents no longer exist.
I cannot see that the average 777 trip length is 3 hours, but I'll stand corrected!

I'm also not sure where the math comes from that the rate is 1/3 that of the B777. If it's because the trip length is 3 times that of the B777 (questionable), then it's wrong - the rates were not the same to start with - the B777 rate was half that of the A340 -> which would make the A340 rate about 2/3 of the B777.

BUT .... I guess it's not worth arguing since we don't have the true data for mechanical turnbacks and diversions - the above interpretation is based on too many assumptions (90%, 3hours vs 10, non-mechanical proportional to trip length etc.)  Wink


BTW that wasn't the actual link I found ... but was referencing it I guess.

Jimbo
I'd rather be on the ground wishing I was in the air, than in the air wishing I was on the ground!
 
David L
Posts: 8551
Joined: Tue May 18, 1999 2:26 am

RE: The Ongoing Two Engines Vs. Four Debate

Sun Feb 11, 2007 7:53 am

Quoting Bond007 (Reply 33):
unless you are BA,

Or one of many other airlines.  Smile

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.

What are the odds of a quad losing thrust from both engines on the same wing during take-off compared to a twin losing thrust from one engine during take-off?

Zeke: Thanks for injecting some first-hand experience into the thread.  Smile
 
redflyer
Posts: 3905
Joined: Thu Feb 24, 2005 3:30 am

RE: The Ongoing Two Engines Vs. Four Debate

Sun Feb 11, 2007 8:11 am

Quoting Zeke (Reply 64):
Quoting RedFlyer (Reply 56):
As others have pointed out, all aircraft -- quad or twin -- should divert to the nearest airport when an engine fails. But that doesn't mean they can't make it to their destination.


That is false see my comments regarding FAR Sec. 121.565 above.

What is false about my comment? FAR 121.565 does not say the aircraft (quad or tri) can continue to its original destination. Unless I'm interpreting it wrong, it's not saying the pilot can continue to his original destination; only giving him the option to choose another suitable airport for landing, other than the nearest suitable airport...

FAR Sec. 121.565 (b): "...the pilot in command may proceed to an airport that he selects if, after considering the following, he decides that proceeding to that airport is as safe as landing at the nearest suitable airport:" (emphasis added)

**********

I suppose if the destination airport is close, but not as close as the nearest suitable airport, then he can continue to the destination airport if he considers all of the factors outlined in sub-paragraph (b) 1 through 6. And according to the FAR he'll have to explain why he did not set down at the nearest suitable airport and why the airport he did select to proceed to was as safe a course of action as landing at the nearest suitable airport he chose to bypass...

FAR Sec 121.565 (d): "If the pilot in command lands at an airport other than the nearest suitable airport, in point of time, he or she shall (upon completing the trip) send a written report, in duplicate, to his or her director of operations stating the reasons for determining that the selection of an airport, other than the nearest airport, was as safe a course of action as landing at the nearest suitable airport." (emphasis added)

I find it interesting that the section identifies the nearest airport "in point of time", not in distance.

**********
So, Zeke, your profile says you're an airline pilot. I presume (although I could be incorrect) that means you fly the big birds. Does your airline in fact encourage its pilots to press on when an engine is out on a quad or tri jet? You realize, of course, pressing on in light of any kind of major equipment failure is, in and of itself, a big risk. I would think it's an even bigger risk than flying intercontinental ocean distances on only 2 engines.

If I were on a plane -- quad or twin -- I would want the pilot to set down at the nearest suitable airport. I think the fact that twins are required to set down at the nearest suitable without allowing the pilot any discretion to decide otherwise probably is an added -- and better -- safety feature of a twin.

I have no issue that you think quads are safer than twins. But that is a dated argument; the manufacturers know it; the airlines know it; and the FARs will eventually reflect it.
A government big enough to take away a constitutionally guaranteed right is a government big enough to take away any guaranteed right. A government big enough to give you everything you need is a government big enough to take away everything you have.
 
bond007
Posts: 4428
Joined: Mon Mar 14, 2005 2:07 am

RE: The Ongoing Two Engines Vs. Four Debate

Sun Feb 11, 2007 8:22 am

Quoting Bond007 (Reply 72):
I cannot see that the average 777 trip length is 3 hours, but I'll stand corrected!



Quoting Bond007 (Reply 72):
If it's because the trip length is 3 times that of the B777 (questionable)

Well, I happen to have data for 5,300 B777 flights departing/arriving the USA (including domestic flights), and the average planned flight length is around 7 1/2 hours. Of course this may not be true across the world, but I cannot see it being 3 hours.

So, if the A340 average flight time is 10 hours, and the average B777 time is around 7.5 hours - there are more mechanical diversions for A340s (since the rate is double for A340s).

I'm not sure why this isn't logical - if you agree there is more chance of a single engine failure (and some don't I know), and that some (or most) of those result in a turnback or diversion -> then it makes sense.

Jimbo
I'd rather be on the ground wishing I was in the air, than in the air wishing I was on the ground!
 
adizzy
Posts: 140
Joined: Tue Jan 16, 2007 12:27 am

RE: The Ongoing Two Engines Vs. Four Debate

Sun Feb 11, 2007 8:45 am

I beg to ask the question:

Why not three engines. Avaiation has become boring becuase all airplanes look so alike these days. We used to atleast have some variation, but no it either has two engines or four engines! I was to see a new version of the 3 engined work horse back!
 
philb
Posts: 2645
Joined: Mon May 24, 1999 5:53 am

RE: The Ongoing Two Engines Vs. Four Debate

Sun Feb 11, 2007 9:11 am

There are a number of problems with three engines, not the least of which are those regarding the position and weight at the rear end of the aircraft.

Modern fans are BIG, even compared to the MD-11 set up. Hanging the engine half way up the tail needs heavy structures to support the engine. Placing it a la the L1011 involves ducting air through an S bend and leads to problems of airflow which grow with engine size.

The balance of the whole airframe has to be worked differently to aircraft with symetrical engines and what was relatively easy to overcome, even up to the days of the MD-11 design, gets much more difficult with today's large fan engines.

Then there is the problem of maintenance. An engine mounted up the tail is more time consuming to deal with on normal turnaround. Doing in situ maintenance or changing it is time consuming and far more expensive than for an underwing engine. The same goes for one buried in the rear fuselage.

All of that goes for conventional fuselage aircraft and current needs and trends - it may be different when the first blended wing airliner is designed for production.
 
ebj1248650
Posts: 1517
Joined: Mon Jun 06, 2005 6:17 am

RE: The Ongoing Two Engines Vs. Four Debate

Sun Feb 11, 2007 9:54 am

Quoting Philb (Reply 23):
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..

It sounds like the thing that makes the 4 engine airliner most practical is the fact that on the very long distance routes (some of them at least) there are few alternate landing sites that are within 120-180 minutes of the time an engine shuts down or is shut down. That being the case, the four engine airplane is a must. However, it follows that if ETOPS times for twin engine airliners are expanded; i.e. 240 minutes or something even greater, the twin works well on all routes. Will we see this. Remains to be seen. But a lot of technology leaps can take place in a relatively short time, so don't count a new ETOPS standard out too quickly.
Dare to dream; dream big!
 
User avatar
flylku
Posts: 597
Joined: Sat Apr 08, 2006 10:44 pm

RE: The Ongoing Two Engines Vs. Four Debate

Sun Feb 11, 2007 9:56 am

Prediction: In a decade, except for the A380, Airbus will have an all twin product line.
...are we there yet?
 
User avatar
zeke
Posts: 15767
Joined: Thu Dec 14, 2006 1:42 pm

RE: The Ongoing Two Engines Vs. Four Debate

Sun Feb 11, 2007 10:42 am

Quoting RedFlyer (Reply 74):
What is false about my comment?

Nearest suitable is only for twins, but that still does mean the closest airport by time or distance, if say with a twin I had an engine failure and needed to divert, and the nearest by time and distance is an airport we are unfamiliar with, has no precision approach, and has not been assessed by the company (I see that as a number of red flag threats), when say 30 min away further we had a company destination, I would be inclined to go for the company destination which is familiar, would have been assessed by the company, has all the rescue and fire toys, and company support.

Quoting RedFlyer (Reply 74):
Unless I'm interpreting it wrong, it's not saying the pilot can continue to his original destination;

Yes you are interpreting it incorrectly, another suitable airport includes the original destination, or point of departure, or the filed alternate, or any other airport the pilot decides is best.

Quoting RedFlyer (Reply 74):
Does your airline in fact encourage its pilots to press on when an engine is out on a quad or tri jet? You realize, of course, pressing on in light of any kind of major equipment failure is, in and of itself, a big risk.

Firstly the airline requires us to think, we are not robots, we can assess the situation, lots of time is available to make a decision. The FMC automatically updates its predictions on either 4, 3 or 2 engines. We have a SAT phone to talk to ops, we will tell them what our options are, and they will tell us their preference, we make the final decision in the cockpit. We can even print out a 3 or 2 engine flight plan out on that is sent from the company via ACARS if required.

We loose zero, zip, no degradation in systems or capability with an engine failure on a quad, all systems are working normally. Depending on my weight I can still maintain my cruise altitude with one engine out.

This is still common practice with many operators, an overweight landing in any aircraft is not something one should need to do unless absolute necessary.

Quoting RedFlyer (Reply 74):
If I were on a plane -- quad or twin -- I would want the pilot to set down at the nearest suitable airport. I think the fact that twins are required to set down at the nearest suitable without allowing the pilot any discretion to decide otherwise probably is an added -- and better -- safety feature of a twin.

Hmm, you are a rare breed, you should have a good look at the airports and normal weather conditions in the north pacific, or across the poles. I address the suitability based on the nature of the situation, I will not divert to some airport in the north pacific with a 60 kt crosswind icy runway and no ILS with an engine that has just stalled, when I could comfortably turn around head for Japan, or continue onto Vancouver, Toronto, or even New York. For an engine fire, I would go to the closest piece of runway I could find, it depends on the situation, thats my job, I get paid to make that sort of decision at the time when all the information is available.

Quoting Bond007 (Reply 75):
I'm not sure why this isn't logical - if you agree there is more chance of a single engine failure (and some don't I know), and that some (or most) of those result in a turnback or diversion -> then it makes sense.

The most common reasons for us to have diversions is medical or weather. If I am departing on a 18 hr trip and have a medical situation arise I will most probably turn back as the flight time is pushing limits for an enroute diversion. We have had very few diversions due to engine failures, all I can say is our internal statistics are not like the ones you mentioned.

The Boeing source I suspect is correct, but only if one knows the full context of the data. If the Boeing data does include non-technical diversions, the comparison is useless. I personally have only had one technical diversion or turn back on an Airbus, and that was on the 320, never had one on a 330 or 340 in a couple thousand sectors.

P.S. CO is the only airline in the states that has usage stats like you claim to have, AA etc average fewer hours per day than CO do on their 777s.
“Don't be a show-off. Never be too proud to turn back. There are old pilots and bold pilots, but no old, bold pilots.” E. Hamilton Lee, 1949
 
GlobalVillage
Posts: 25
Joined: Mon Oct 30, 2006 5:36 pm

RE: The Ongoing Two Engines Vs. Four Debate

Sun Feb 11, 2007 10:46 am

Quoting Zeke (Reply 19):
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".

You have to also remember that a quad is "statistically" more likely to have one or more engines fail. Plus, it's most likely that a quad will divert anyway.
 
bond007
Posts: 4428
Joined: Mon Mar 14, 2005 2:07 am

RE: The Ongoing Two Engines Vs. Four Debate

Sun Feb 11, 2007 10:54 am

Quoting Zeke (Reply 80):
The most common reasons for us to have diversions is medical or weather. If I am departing on a 18 hr trip and have a medical situation arise I will most probably turn back as the flight time is pushing limits for an enroute diversion. We have had very few diversions due to engine failures, all I can say is our internal statistics are not like the ones you mentioned.

I'm not disagreeing (and how could I) - yes, 90% of diversions are non-mechanical. I was purely being anal and saying that statistically anyway, the figures point towards more potential diversions with quad vs twin - albiet extremely small probabilites, as you confirm from real-world experiences.

Quoting Zeke (Reply 80):
P.S. CO is the only airline in the states that has usage stats like you claim to have, AA etc average fewer hours per day than CO do on their 777s.

My stats aren't usage per se - just average hours per flight. 3 hours seemed extremely small for an average B777 flight, and it appeared incorrect. Yes, the figures maybe skewed by COs 777 flights EWR to VHHH or wherever, but that's what averages are all about and why we have them right  Wink


Jimbo
I'd rather be on the ground wishing I was in the air, than in the air wishing I was on the ground!
 
User avatar
zeke
Posts: 15767
Joined: Thu Dec 14, 2006 1:42 pm

RE: The Ongoing Two Engines Vs. Four Debate

Sun Feb 11, 2007 11:00 am

Quoting GlobalVillage (Reply 81):
You have to also remember that a quad is "statistically" more likely to have one or more engines fail. Plus, it's most likely that a quad will divert anyway.

Have look at reply 65 for my reasons why i think that is wrong.

QF for example kept on going to SYD last year in a 747, and turned back to SYD just recently in a 747. But I seem to recall more failures and diversions with the 737 and 767 at QF, think you will find the QF 744 fleet would have fewer technical diversions than the twin engine fleet.
“Don't be a show-off. Never be too proud to turn back. There are old pilots and bold pilots, but no old, bold pilots.” E. Hamilton Lee, 1949
 
David L
Posts: 8551
Joined: Tue May 18, 1999 2:26 am

RE: The Ongoing Two Engines Vs. Four Debate

Sun Feb 11, 2007 11:17 am

Quoting RedFlyer (Reply 74):
Does your airline in fact encourage its pilots to press on when an engine is out on a quad or tri jet? You realize, of course, pressing on in light of any kind of major equipment failure is, in and of itself, a big risk. I would think it's an even bigger risk than flying intercontinental ocean distances on only 2 engines.

In case Zeke and others don't want to go through the whole thing yet again, you might want to take a look at these discussions with input from several quad pilots (including Zeke, of course):
BA 744 Flies LAX-MAN With 3 Engines...WITH Pax! (by Pacific Feb 25 2005 in Civil Aviation) RE: FAA Drops Its 3 Engine 744 Case Against BA (by David L Sep 26 2006 in Civil Aviation) RE: BA Pilot Flies Despite Fire On 747 (by David L Sep 26 2006 in Civil Aviation)
(there was no fire!)

Quoting RedFlyer (Reply 74):
I think the fact that twins are required to set down at the nearest suitable without allowing the pilot any discretion to decide otherwise probably is an added -- and better -- safety feature of a twin.

I suspect that might have more to do with a twin only having one remaining engine after a single engine failure, don't you?
 
777ER
Head Moderator
Posts: 10132
Joined: Fri Dec 19, 2003 5:04 pm

RE: The Ongoing Two Engines Vs. Four Debate

Sun Feb 11, 2007 11:24 am

Quoting Mariner (Reply 8):
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.

I know he didnt say it

Quoting Baroque (Reply 10):
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.

B747s are more kinder towards fuel then the A340s
Head Forum Moderator
[email protected]
Flown: 1900D,S340,Q300,AT72-5/6,DC3,CR2/7,E145,E70/75/90,A319/20/21,A332/3,A359,A380,F100,B717,B733/4/8/9,B742/4,B752/3,B763,B772/3, B789
With: NZ,SJ,QF,JQ,EK,VA,AA,UA,DL,FL,AC,FJ,SQ,TG,PR
 
redflyer
Posts: 3905
Joined: Thu Feb 24, 2005 3:30 am

RE: The Ongoing Two Engines Vs. Four Debate

Sun Feb 11, 2007 12:46 pm

Quoting Zeke (Reply 80):
but that still does mean the closest airport by time or distance

You better go back and read your own FAR 121.565, which you are relying on for your argument. It's very specific: "in point of time". No mention is made of distance.

Quoting Zeke (Reply 80):
Yes you are interpreting it incorrectly, another suitable airport includes the original destination, or point of departure, or the filed alternate, or any other airport the pilot decides is best.

Yes, I know very well another "suitable airport" may include the original destination or point of departure (I said so in my reply #74). However, the pilot does not have total discretion. The FAR is very specific in stating that the chosen airport, if it's different than the nearest suitable airport, must be "as safe a course of action" as the nearest suitable airport.

Quoting Zeke (Reply 80):
We loose zero, zip, no degradation in systems or capability

Well, there you are in fact wrong because while you may not incur degradation in systems, you will assuredly lose degradation in capability with an engine out.

[Edited 2007-02-11 04:47:03]
A government big enough to take away a constitutionally guaranteed right is a government big enough to take away any guaranteed right. A government big enough to give you everything you need is a government big enough to take away everything you have.
 
JAAlbert
Posts: 1980
Joined: Tue Jan 31, 2006 12:43 pm

RE: The Ongoing Two Engines Vs. Four Debate

Sun Feb 11, 2007 1:47 pm

Quoting Jasond (Reply 17):
and there is the safety factor with two extra power plants.

I think this is the point -- research shows that planes with two extra power plants aren't any safer. The 4 engine safety argument is based on fallacy. The passenger may feel reassured with a couple of extra engines hanging off the wings, but in reality he/she is not.
 
redflyer
Posts: 3905
Joined: Thu Feb 24, 2005 3:30 am

RE: The Ongoing Two Engines Vs. Four Debate

Sun Feb 11, 2007 2:26 pm

Quoting David L (Reply 84):
In case Zeke and others don't want to go through the whole thing yet again, you might want to take a look at these discussions with input from several quad pilots (including Zeke, of course):

BA 744 Flies LAX-MAN With 3 Engines...WITH Pax! (by Pacific Feb 25 2005 in Civil Aviation)
RE: FAA Drops Its 3 Engine 744 Case Against BA (by David L Sep 26 2006 in Civil Aviation)
RE: BA Pilot Flies Despite Fire On 747

Sorry to burst your bubble, but that was ONE incident. Care to reference any others? And the fact that the FAA dropped the matter does not mean they condoned the decision to continue the flight. This was as much a political matter as it was a safety of flight issue. In passing judgment on the BA flight the FAA would have been delving into matters reserved for the CAA.

But, hey, if you want to think that was a sound judgment by BA to continue that flight then by all means, have it your way.

Quoting David L (Reply 84):
I suspect that might have more to do with a twin only having one remaining engine after a single engine failure, don't you?

Well, DUH! Of course it has to do with a twin having only one remaining engine! But when the regs are clear and they very specifically do not allow a pilot to make any other decision other than to fly to the nearest suitable airport, how often do you think that a divert by a twin (with one engine operating) will encounter further problems enroute to the nearest suitable airport?

On the other hand, if a pilot has discretion to choose an airport further away than the nearest suitable airport, don't you think there is a slightly increased chance (however small it may be) that further problems will be encountered en route to that airport? And don't forget: the human is most often times the weakest link in a chain of events.

That is why I said that the fact a twin MUST divert to the nearest suitable airport will in fact make it safer than a quad that is allowed to continue, based on human judgment, to another, farther away, suitable airport.
A government big enough to take away a constitutionally guaranteed right is a government big enough to take away any guaranteed right. A government big enough to give you everything you need is a government big enough to take away everything you have.
 
jasond
Posts: 648
Joined: Fri Jul 10, 2009 5:23 am

RE: The Ongoing Two Engines Vs. Four Debate

Sun Feb 11, 2007 2:44 pm

Quoting JAAlbert (Reply 87):
I think this is the point -- research shows that planes with two extra power plants aren't any safer. The 4 engine safety argument is based on fallacy. The passenger may feel reassured with a couple of extra engines hanging off the wings, but in reality he/she is not.

Well maybe I should have qualified that with 'perceived' safety factor. For what it's worth I have always felt 'safer' on 4's rather than 2's, personal opinion only.
 
OldAeroGuy
Posts: 3928
Joined: Sun Dec 05, 2004 6:50 am

RE: The Ongoing Two Engines Vs. Four Debate

Sun Feb 11, 2007 4:02 pm

Quoting ZANL188 (Reply 26):
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.

Quoting anecdotal events to prove one design is more safe than another is a fundamentally bad practice. The overall accident statistics don't back up your assertion that Twins are fundamentally safer than Quads. See my further comments below on takeoff probabilities.

Quoting Zeke (Reply 37):
Welcome to China.

Do you expect me to believe that all 1.3 billion people in China buy an average of 7 to 8 lotto tickets each week? That's what it would take to have 1 in 10 billion odds in a lotto game with a winner every week. Please substantiate these odds and winning rate or admit it's incorrect. You should quote a realistic example if you're going to make a similarity argument to ETOPS operational requirements.

If you're talking about overall risk levels, Twin and Quad regulatory requirements for systems other than engines say a catastrophic event can occur once every 1,000,000,000 flight hours. While individual designs may differ, the regulatory system requirements for a "safe" airplane (FAR 25.1309) are the same for Twins, Tris, and Quads.

Quoting Zeke (Reply 37):
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.

Not necessarily true except in the propulsion arena. As an example, the A340, A330 and the 777 all have three hydraulic systems. Loss of all fluid from all three systems would constitute a catastrophic event for all of these airplanes. If you don't have hydraulics, you can't move the flight control surfaces and that will make it a bad day.

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.

This is really a poor argument. The probability for an engine failure during takeoff is on the order of 1 in 100,000 or more takeoffs. The probability of two engines failing during takeoff on either a Twin or a Quad is on the order of 1 in 10,000,000,000 takeoffs. There is no need to certify an airplane to an event of this low probability.

Quoting Zeke (Reply 64):
This is false, you really need to have a look at FAR 25.100 series , a summary is below.

The table you provided is for one engine inoperative. To achieve these levels, Twins operate at higher T/W's than Quads for all engine operation. This does give the Twin an advantage in countering adverse events (like windshear) that occur during takeoff. Since engine failures during takeoff occur about once in every 100,000 or more takeoffs, day-by-day operations do favor the Twin when it comes to having greater performance capability during all engine operation.
Airplane design is easy, the difficulty is getting them to fly - Barnes Wallis
 
User avatar
kc135topboom
Posts: 11205
Joined: Sun Jan 30, 2005 2:26 am

RE: The Ongoing Two Engines Vs. Four Debate

Sun Feb 11, 2007 4:17 pm

Quoting ZANL188 (Reply 25):
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.

There was one that came close. IIRC, it was an A-330 that ran out of fuel and glided into the Azores a few years ago.
 
User avatar
NWAROOSTER
Posts: 1379
Joined: Mon Feb 14, 2005 2:29 pm

RE: The Ongoing Two Engines Vs. Four Debate

Sun Feb 11, 2007 4:32 pm

The British Airways 747 that lost an engine on takeoff from LAX was supposed to fly to LHR. The pilot, with British Airways approval, decided to continue the fight to LHR. This was a dumb mistake as the aircraft had to divert to MAN in England as it was running low on Fuel. Four engine aircraft maybe safer to operate, but they do have twice the change of an engine failure, just due to the fact they have two EXTRA engines This gives the pilot to prudently pick an airport to land at short of his original destination. It does NOT give him the right to continue the flight, to its original destination, when it is thousands of miles away.
Safety always comes FIRST.
Procrastination Is The Theft Of Time.......
 
OldAeroGuy
Posts: 3928
Joined: Sun Dec 05, 2004 6:50 am

RE: The Ongoing Two Engines Vs. Four Debate

Sun Feb 11, 2007 4:49 pm

Quoting Philb (Reply 5):
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.



Quoting OldAeroGuy (Reply 29):
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.



Quoting Philb (Reply 32):
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..

The largest customer for the 772LR is Emirates with 10. Prior to that order, they were flying 10 A345's. If commonality was a primary factor and Twins are not suitable for ultralong haul routes as you assert, why didn't Emirates re-order A345's?
Airplane design is easy, the difficulty is getting them to fly - Barnes Wallis
 
philb
Posts: 2645
Joined: Mon May 24, 1999 5:53 am

RE: The Ongoing Two Engines Vs. Four Debate

Sun Feb 11, 2007 7:28 pm

Emirates, as you are well aware, splits its fleet between Boeing and Airbus. As it happens, if you look at Emirates routes, only Dubai-JFK comes under the 180 minute rule, and then only at certain times of the year when it tracks over the Arctic rather than across the standard Atlantic tracks as at present..

Quoting OldAeroGuy (Reply 93):
and Twins are not suitable for ultralong haul routes as you assert,

I didn't make that assertion. There are many ultra long haul routes well within the 180 minute rule LHR-SYD, LHR-LAX, LHR-JNB for instance.

Where the suitability of twins comes into play is on routes where there are large segments with 120 plus minutes to one or few suitable airports
 
User avatar
zeke
Posts: 15767
Joined: Thu Dec 14, 2006 1:42 pm

RE: The Ongoing Two Engines Vs. Four Debate

Sun Feb 11, 2007 8:08 pm

Quoting OldAeroGuy (Reply 90):
Do you expect me to believe that all 1.3 billion people in China buy an average of 7 to 8 lotto tickets each week? That's what it would take to have 1 in 10 billion odds in a lotto game with a winner every week.

from http://en.safetourchina.com/English/news_detail.asp?id=3168

"China s lottery sales in 2006 increased 10.54 billion yuan from the previous year to a record high of 81.93 billion yuan (US$105.4 billion), said the Chinese Ministry of Finance on Thursday.", each ticket is less than US$0.25.

"Excluding the eight days around the Spring Festival when lottery sales were suspended, every day about 229 million yuan (US$29.5 million) of lottery tickets were sold in China in 2006."

As for finding a link with the actual odds, I cannot read Chinese, so I unable to help you, however I did see on wiki

"Lottery: The odds of winning the Grand Prize (matching all 6 numbers) in the US Powerball Multistate Lottery, with a single ticket, under the rules as of 2006, are 146,107,962 to 1 against, for a probability of 7�---10-9.
Lottery: The odds of winning the Jackpot (matching the 6 main numbers) in the UK National Lottery, with a single ticket, under the rules as of 2003, are 13,983,816 to 1 against, for a probability of 7�---10-8."

From your link I found "For type design approval up to and including 180 minutes: An IFSD rate of 0.02 or less per 1,000 world-fleet engine-hours", I did not find the stats you mentioned above.

Quoting OldAeroGuy (Reply 90):
If you don't have hydraulics, you can't move the flight control surfaces and that will make it a bad day.

345/346 has electric backup on the THS, 380 has further electric backup to include roll and pitch control.

Quoting OldAeroGuy (Reply 90):
This does give the Twin an advantage in countering adverse events (like windshear) that occur during takeoff.

I would disagree, our 340s and 747s have a lot more inertia, the lighter the aircraft the greater the effect of windshear. Large ships handle heavy seas better than smaller boats, regardless of the T/W ratio.

Quoting OldAeroGuy (Reply 93):
The largest customer for the 772LR is Emirates with 10. Prior to that order, they were flying 10 A345's. If commonality was a primary factor and Twins are not suitable for ultralong haul routes as you assert, why didn't Emirates re-order A345's?

Was that not AC ? and have they not recently converted 3 more 772LRs to 773ERs ?

Of all the 772LRs that are in service, how many are actually doing ULH, how does that compare to the 345 ?

Are people buying the 772LR because the 772ER is basically unavailable or has little resale value ?
“Don't be a show-off. Never be too proud to turn back. There are old pilots and bold pilots, but no old, bold pilots.” E. Hamilton Lee, 1949
 
David L
Posts: 8551
Joined: Tue May 18, 1999 2:26 am

RE: The Ongoing Two Engines Vs. Four Debate

Sun Feb 11, 2007 8:15 pm

Quoting RedFlyer (Reply 88):
Sorry to burst your bubble, but that was ONE incident. Care to reference any others?

I suggested reading the threads, not just the thread titles. Read the comments from pilots from other airlines who actually fly quads.

Quoting Nwarooster (Reply 92):
This was a dumb mistake as the aircraft had to divert to MAN in England as it was running low on Fuel.

1. They did not divert to MAN because they had an engine out, they diverted because they thought they had less fuel available to them than they had - read the linked threads.
2. What difference does it make whether they diverted to MAN or any of the US and Canadian alternates on the way, plus KEF, SNN, DUB, PIK, GLA, etc? The point is that they were always within range of an alternate even if another engine had failed. Check the linked threads.
 
intermodal64
Posts: 83
Joined: Mon May 29, 2006 10:53 pm

RE: The Ongoing Two Engines Vs. Four Debate

Mon Feb 12, 2007 1:25 am

If we assume for the moment that the difference in safety between 2 and 4 engines is insignificant, when does it make economic sense to operate 4 vs 2? Related to this, why does the A-340 seem to have a reputation as an expensive fuel guzzler while the 747 is recognized as an efficient aircraft? (I'm not picking on the A-340. I actually prefer it as a passenger -- no logical reason I can put my finger on.)
 
bond007
Posts: 4428
Joined: Mon Mar 14, 2005 2:07 am

RE: The Ongoing Two Engines Vs. Four Debate

Mon Feb 12, 2007 1:32 am

Quoting David L (Reply 96):
They did not divert to MAN because they had an engine out, they diverted because they thought they had less fuel available to them than they had - read the linked threads.

So they would have landed at MAN even they didn't have an engine out then??

...and yes, I checked the linked threads.


Jimbo
I'd rather be on the ground wishing I was in the air, than in the air wishing I was on the ground!
 
redflyer
Posts: 3905
Joined: Thu Feb 24, 2005 3:30 am

RE: The Ongoing Two Engines Vs. Four Debate

Mon Feb 12, 2007 1:45 am

Quoting David L (Reply 96):
I suggested reading the threads, not just the thread titles. Read the comments from pilots from other airlines who actually fly quads.

Sorry, I've got better things to do than to read 350+ posts (in addition to user profiles) and try to figure out the few that supposedly buttress your point of view regarding quads and the fact that the BA flight was conducting in as safe a manner as any other normal flight. If you want to point to any specific ones and reference them here, then by all means do so. But you can probably save your time because for every one you point to me I could probably find 2 from actual airline pilots I know (as well as from professional journals) -- and not just wannabe pilots on A.Net -- that will tell you BA was wrong and the flight put the aircraft and its passengers at unnecessary risk.

Somehow you've interpreted the FAA's decision to not pursue the matter under FAR 121.565 as condoning the conduct of the flight by the crew and BA. That was not the case. If you read up on the history of the matter the FAA dropped it for political reasons because it did not want to lock horns with the CAA. In short, it was a political decision that in no way reflected nor addressed the safety of the flight or the conduct of the crew in continuing the flight.
A government big enough to take away a constitutionally guaranteed right is a government big enough to take away any guaranteed right. A government big enough to give you everything you need is a government big enough to take away everything you have.

Popular Searches On Airliners.net

Top Photos of Last:   24 Hours  •  48 Hours  •  7 Days  •  30 Days  •  180 Days  •  365 Days  •  All Time

Military Aircraft Every type from fighters to helicopters from air forces around the globe

Classic Airliners Props and jets from the good old days

Flight Decks Views from inside the cockpit

Aircraft Cabins Passenger cabin shots showing seat arrangements as well as cargo aircraft interior

Cargo Aircraft Pictures of great freighter aircraft

Government Aircraft Aircraft flying government officials

Helicopters Our large helicopter section. Both military and civil versions

Blimps / Airships Everything from the Goodyear blimp to the Zeppelin

Night Photos Beautiful shots taken while the sun is below the horizon

Accidents Accident, incident and crash related photos

Air to Air Photos taken by airborne photographers of airborne aircraft

Special Paint Schemes Aircraft painted in beautiful and original liveries

Airport Overviews Airport overviews from the air or ground

Tails and Winglets Tail and Winglet closeups with beautiful airline logos