Go Back  PPRuNe Forums > PPRuNe Worldwide > The Pacific: General Aviation & Questions
Reload this Page >

Statistically, when will a large twin engine jet end up in the drink?

The Pacific: General Aviation & Questions The place for students, instructors and charter guys in Oz, NZ and the rest of Oceania.

Statistically, when will a large twin engine jet end up in the drink?

Reply

Old 2nd Jan 2019, 09:55
  #21 (permalink)  
 
Join Date: Feb 2008
Location: DORSET
Age: 61
Posts: 231
Not just engine failure/loss of power (including loss of both engines - think Air Transat A330 fuel leak) plus cargo hold fires (SAA 747 Mauritius)
We have also has seen a couple of complete electrical failures on big ETOPS twins (Just last month a LATAM 777-300 on its way to LHR)

ETOPS has been around for 30 years now with the first UK ops with Monarch London to Orlando with the 757-200 via Bangor -
Nowadays the vast majority of long haul over water operations are using large twin engined aircraft with a fair number still using older jets like the 767-300 757-200 and first generation 777 and A330's on such missions - aircraft and engines with high time cycles.
AND brand new twin jets with new advanced engine technology which has already shown some weaknesses in service due to manufacturing and or design defects (RR 787 and LEAP etc)

One has to wonder that statistically an 'event' is more likely to occur (V.V say 10-15 years ago) as twin jet usage increases, time, age and possibly unproven in-service life go on.
rog747 is offline  
Reply With Quote
Old 2nd Jan 2019, 11:27
  #22 (permalink)  
 
Join Date: Apr 1998
Location: Mesopotamos
Posts: 1,132
I've often wondered why something as horrendously expensive as an F-35 only has one engine?
The answer is that there has been a small revolution in the manufacturing industry using CAD/CAM software at a new level. More complexity and more failsafe can now be built into the inherent designs with less hands-on human involvement in the manufacturing process. The end result being you get what you designed for quicker, cheaper and to spec.

But in my opinion we are still not quite there yet with human oversight still creeping into the designs in ways never considered e.g impurity levels in base materials, running a crucial oil pipe through the hot section of a turbine, software flaws, etc, etc.

Add to this equation that engine thrust levels have been increasing rapidly creating much less need for more engines under the wings to achieve a similar performance. This means bigger aircraft like the A380 can now be built out of all that extra power, but is it any safer? 747s have fallen out of the sky and often it was not because of the added safety of having 4 engines. Then their was that early model A340 which had these 4 wimpy engines and seemed to require all of the runway to leap into the air.

2 engines are good and 4 engines are better, and as long as we don't kid ourselves about an aircraft's abilities during degraded performance the 2 engine variety should continue to serve us well into the future as they get even more powerful. By then we will be arguing about having only one engine which is already a contentious issue in helicopter land.
cattletruck is offline  
Reply With Quote
Old 2nd Jan 2019, 15:56
  #23 (permalink)  
 
Join Date: Nov 2015
Location: Farnham, Surrey
Posts: 1,111
A rational line or reasoning might run something like this:

1. Is double-engine-failure the only "single" event that would inherently bring down an aeroplane when over the ocean? If no then:

2. Is the probability of a double engine failure higher than the probability of those other events? If no then:

3. Why are you fixated with engine failure when you're prepared to accept a similar probability of crashing or ditching in the ocean as a result of more probable events?

It is my understanding that the whole ETOPS thing came about because it dawned on people that they were demanding higher reliability from the engines than they were from other items which were just as critical to continued flight, and that's just not a rational thing to do. So instead of saying "Thou shalt have at least four engines*" they said "Thou shalt have a probability of failures (engine or anythingh else) sufficient to prevent continued flight of less than x".

PDR

* What's so magical about the number 4? WHy isn't it 5, 6, 7, 10, 20, 100 or WHY? That's what demonstrates the whole concept of dictating a number of engines rather than a system reliability performance is just irrational
PDR1 is offline  
Reply With Quote
Old 2nd Jan 2019, 16:12
  #24 (permalink)  

Avoid imitations
 
Join Date: Nov 2000
Location: Wandering the FIR and cyberspace often at highly unsociable times
Posts: 11,847
Originally Posted by Tankengine View Post
The most likely cause of both engines failing at the same time is fuel contamination, which would also affect a four engine aircraft.
Just like doing a mag plug change on all engines at the same time and not completing the second part of the job.....
ShyTorque is online now  
Reply With Quote
Old 2nd Jan 2019, 18:04
  #25 (permalink)  
 
Join Date: Nov 2005
Location: London
Posts: 512
Dick Smith

For those that say the twin engine operations are just as safe, why do the ICAO regulations still require four engine operations for flights from say, Australia to South America. Surely if the twin was just as safe, it would be approved.
ICAO do not require 4 engines on any route. The state decides and if the twin can be shown to be "just as safe" it is EDTO certified and is "approved". Hence twin jets do operate direct between Oz and South America.

With more and more EDTO throughout the world (literally millions of hours), statistically someone must have worked out when one of these aircraft is going to end up in the drink. That is, originally there is a single engine failure, and before it can get to the alternate and land , the other engine fails. I have recently been told that statistically we are over that time and the safety experts are wondering when such a disaster will happen.
And you were told that this event is more likely to occur during ETOPS whilst 1 to 3 hours from a runway than it is on the entirety of the rest of the world's twins operating non-ETOPS?
oggers is online now  
Reply With Quote
Old 2nd Jan 2019, 18:17
  #26 (permalink)  
swh

Eidolon
 
Join Date: May 2001
Location: Some hole
Posts: 1,890
Originally Posted by Dick Smith View Post

For those that say the twin engine operations are just as safe, why do the ICAO regulations still require four engine operations for flights from say, Australia to South America. Surely if the twin was just as safe, it would be approved.

.
ICAO have standards and recommend practices which are implemented by individual states.

Not aware of any restrictions on a twin operating over the South Pole other than having to remain within the approved engine out diversion time. At the moment even with a 5.5 hour (330 minute) diversion time (around 2300 nm) there is still a big gap between Australia and the South Pole.

A PER-EZE flight could not be planned via the great circle route as there is a gap between Hobart and Ushuaia even with a 330 minute diversion time where MEL-EZE could.

Quads follow ETOPS beyond 180 minutes.
swh is offline  
Reply With Quote
Old 2nd Jan 2019, 19:37
  #27 (permalink)  
 
Join Date: Jul 2013
Location: Everett, WA
Age: 63
Posts: 1,915
Originally Posted by PDR1 View Post
A rational line or reasoning might run something like this:

1. Is double-engine-failure the only "single" event that would inherently bring down an aeroplane when over the ocean? If no then:

2. Is the probability of a double engine failure higher than the probability of those other events? If no then:

3. Why are you fixated with engine failure when you're prepared to accept a similar probability of crashing or ditching in the ocean as a result of more probable events?
Exactly - there are many reasons why aircraft crash, the engines are just one. And adding engines doesn't necessarily even make the propulsion contribution to safety better. It's historically been very, very rare that an aircraft crashes due to a 'simple' engine failure (and when it's happened it was not due to the engine failure as such but inappropriate crew action - such as shutting down the wrong engine). However, what historically hasn't been so rare are crashes due to catastrophic engine failures - e.g. uncontained failures or fires (Sioux City DC-10, and the Qantas A380 near miss being two examples). Increasing the number of engines increases the likelyhood of a catastrophic engine failure. If you run the statistics, having more than two engines does not improve the risk numbers for an engine caused accident.

Originally Posted by PDR1 View Post
A rational line or reasoning might run something like this:
It is my understanding that the whole ETOPS thing came about because it dawned on people that they were demanding higher reliability from the engines than they were from other items which were just as critical to continued flight, and that's just not a rational thing to do. So instead of saying "Thou shalt have at least four engines*" they said "Thou shalt have a probability of failures (engine or anythingh else) sufficient to prevent continued flight of less than x".

PDR

* What's so magical about the number 4? WHy isn't it 5, 6, 7, 10, 20, 100 or WHY? That's what demonstrates the whole concept of dictating a number of engines rather than a system reliability performance is just irrational
Yep
tdracer is offline  
Reply With Quote
Old 2nd Jan 2019, 20:44
  #28 (permalink)  
 
Join Date: Dec 2001
Location: YMML
Posts: 2,419
Interesting thought. However, the design parameter of engine size and number is dependent on available technology. Imagine if, back in the early sixties, an engine of Trent size was available instead of an RB211 size....what would a 747 have looked like with that type of power availability. Same size on two engines or supersized on four. Surely, the design parameter of excess power equals performance is more important than how far you can stay in the air on one. The job is to get the weight to the design cruise level economically. After that, the envelope gets looked at on how far can you fly on whats left at lower altitude on higher specific fuel flows...isnt that what ETOPS was all about...not running out of fuel rather than the stats of a catastrophic failure?

If the stats become king then...as witnessed by the Hudson River event...you would not launch because it CAN happen!

Obviously above my pay grade but isnt that the gist of ETOPS?
OZBUSDRIVER is offline  
Reply With Quote
Old 2nd Jan 2019, 20:47
  #29 (permalink)  
 
Join Date: Aug 2008
Location: Auckland
Posts: 95
You assume the independency of the events, which is not true in general - you need to factor in the dependency through fuel problems.


The engine can either work (P=6/7) or fail (P=1/7).
Let's look at the probability of the independent events.
1.P(W1,W2)=P(W1)*P(W2)=6/7*6/7=36/49
2.P(W1,F2)=P(W1)*P(F2)=6/7*1/7=6/49
3.P(F1,W2)=P(F1)*P(W2)=1/7*6/7=6/49
4.P(F1,F2)=P(F1)*P(F2)=1/7*1/7=1/49
sgenie is offline  
Reply With Quote
Old 2nd Jan 2019, 21:19
  #30 (permalink)  
 
Join Date: Jul 2007
Location: Australia
Age: 68
Posts: 211
Dick. You are pushing a barrow. Leave ETOPS (however we name it) to professionals. There has never been a better researched and analysed piece of aviation than ETOPS except . CASA didn't start it. Australia's rules are little different than anyone elses. Industry professionals live the well-understood "chronic unease" wondering what single point of failure problem might have been thus far un-noticed. Could even be two pilots getting their (contaminated) coffee from the same coffee stall before departure and both becoming disabled at the same time. Why not carry a third pilot just in case? If dual un-related engine failures (and then consequences thereof) were the only problem left to solve we would all be smiling. Dual but related engine failures can happen on any flight.

You know as well as anyone that "Safety" has never been the same as "Assurance" or "Guarantee". How about you read Annex 6 and Annex 19 and get back to your readership? You might notice these points:
  • Controlled risk and controlled error is acceptable in an inherently safe system.
  • Safety is a systems property, it can only be determined for the whole system under consideration.
  • Safety constraints need to be enforced at all system levels. SMS provides the framework for this to happen in a systematic way.
Exclaiming surprise that you alone have found something that no-one else has and that therefore CASA is at fault and the Act must be changed might make you feel good but does nothing for the real world.
Captain Sherm is offline  
Reply With Quote
Old 2nd Jan 2019, 21:29
  #31 (permalink)  
 
Join Date: Dec 2014
Location: Nz
Posts: 173
What about the dependency through mechanical damage ( engine bits severing fuel lines, fly by wire cables etc)?
73qanda is online now  
Reply With Quote
Old 2nd Jan 2019, 22:33
  #32 (permalink)  
 
Join Date: Dec 2010
Location: Goolwa
Age: 54
Posts: 105
I think the point of the original post is to build a logical argument along the lines of;

The Act states that safety is the primary concern.
CASA therefore creates and enforces regulation without consideration of economical factors.
Thus the regulations concerning GA, CSF, SIDS etc. do not take into account economic factors.
BUT
CASA allows ETOPS
Statistically four engines are better than two
CASA has allowed regulations that take into account economic viability FOR AIRLINES
This is against the ACT
SO
Either change the Act to reflect that economic factors should be considered when making and enforcing regulation for ALL LEVELS OF AVIATION.
OR
Stop lying about "Safety comes first".
Dexta is offline  
Reply With Quote
Old 2nd Jan 2019, 22:49
  #33 (permalink)  
 
Join Date: Apr 2002
Location: Australia
Posts: 257
Perhaps it just comes down to "affordable safety".
Kelly Slater is offline  
Reply With Quote
Old 2nd Jan 2019, 22:53
  #34 (permalink)  
 
Join Date: Jul 2013
Location: Everett, WA
Age: 63
Posts: 1,915
Originally Posted by Dexta View Post
Statistically four engines are better than two
FALSE!
Statistically ETOPS twins are at least as safe as quads. If you want to argue otherwise you'd better show up with some data.
And before you bring up the A320 that landed in the Hudson, quads have crashed after a birdstrike on takeoff...
tdracer is offline  
Reply With Quote
Old 3rd Jan 2019, 01:57
  #35 (permalink)  
Thread Starter
 
Join Date: May 2002
Location: Australia
Posts: 4,067
Dexta and Kelly ,Exactly what I am getting at!
Dick Smith is offline  
Reply With Quote
Old 3rd Jan 2019, 02:17
  #36 (permalink)  
 
Join Date: Apr 2013
Location: down under
Posts: 274
Originally Posted by Lead Balloon View Post
1976? I suspect there have been some technical advances since then.
in the 737??
cooperplace is offline  
Reply With Quote
Old 3rd Jan 2019, 02:47
  #37 (permalink)  
 
Join Date: Oct 2012
Location: Adelaide
Posts: 506
Dick, while I can sort of see what angle you are going for the reality is that you are pushing shit up hill with a stick.

The reactionary world in which we currently live - where someone does something dumb and kills or injures themselves immediately results in legislation (or at very least pollies on the idiot box calling for legislation) means that your chances of getting some sense in terms of a safety vs cost argument are slim to none.

We as a community kill more people through medical errors than we do through aviation accidents yet we focus on absolute safety in aviation because it plays well to the uninformed. The medical community is very good at couching failures as unintended negative outcomes and people accept that because each human's physiology is different and people understand that sometimes people just die. Crash an aeroplane and it is almost immediately pilot error as the default position until proven otherwise (note the various "experts" commenting (with no solid information other than their "experience") on recent accidents - yes I am looking at you BB)

What i am trying to say, however poorly, is that aviation is an extraordinary activity that has been made ordinary because we apply rigid processes and training to the practice of aviation. Because it is so "everyday" people become blasť about it and are surprised when something goes pear shaped - when in reality the fact is they shouldn't be - driving a couple of hundred tonnes of metal with thousands of moving parts at breakneck speed in a hostile environment whilst carrying a shitload of explosive fuel is, in my opinion, extraordinary, and amazingly safe despite all the things that could possibly go wrong.

If the medical profession had the safety record that aviation does then there would be a lot more people alive world-wide.

But what do we really expect in a community that obsesses with cars driving 1km/h over an arbitrary speed limit and then telling the drivers that they are reckless and irresponsible - and by doing so take the focus away from the big picture which is driving safely within the conditions and making them divert their attention to the speedo at the expense of situational awareness.

Last edited by Snakecharma; 3rd Jan 2019 at 06:34.
Snakecharma is offline  
Reply With Quote
Old 3rd Jan 2019, 03:37
  #38 (permalink)  
 
Join Date: Jul 2013
Location: Everett, WA
Age: 63
Posts: 1,915
Originally Posted by Dick Smith View Post
Dexta and Kelly ,Exactly what I am getting at!
Dick, exactly what I'm getting at. You claim an ETOPS twin is less safe than a quad, but provide zero data or evidence other than your gut feeling. Aviation safety is all about statistics.
Unless you can provide data to back up your claim, it's just another internet claim - which are a dime a billion.
tdracer is offline  
Reply With Quote
Old 3rd Jan 2019, 05:59
  #39 (permalink)  
 
Join Date: Nov 2001
Location: Australia/India
Posts: 2,491
Aviation safety is all about statistics.
So true. And so untrue.

The “statistics” show that pilots with CVD are able to pass licence, rating and recurrent checks to the same standard as pilots without CVD. Yet...

The “statistics” show that piston engine manufacturers’ TBOs are ar*e plucks, and that changing a well-run and well-running piston engine at TBO is merely buying risk. Yet...

Aviation safety is mostly about manipulating or ignoring statistics in favour of intuition or the promotion of well-entrenched special interests.
Lead Balloon is offline  
Reply With Quote
Old 3rd Jan 2019, 06:08
  #40 (permalink)  
Thread Starter
 
Join Date: May 2002
Location: Australia
Posts: 4,067
TDracer. I have not made any claim based on gut feeling.

I take advice from experts. And I use commonsense to decide which advice is correct when there are differences.

I can can see why you post anonymously!
Dick Smith is offline  
Reply With Quote

Thread Tools
Search this Thread

Contact Us Archive Advertising Cookie Policy Privacy Statement Terms of Service