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

[Dick Smith]

Earlier last year I started a controversial thread in relation to ETOPS. In one of the posts I quoted a professional pilot:

“The engines are very reliable these days, so the chance of even one of them to stop functioning is low.

Four engined airplanes are more expensive to maintain and even to buy than twin engine airplanes. This is not what airlines want, they want an airplane that is very economical and reliable because it is a business and business is always about making profits.”
This seemed a reasonable explanation to me and it shows clearly in this case CASA did not consider safety as the most important consideration, but airline profitability and more people being able to participate in the safest form of transport.

However I have a question to ask. 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.

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.

I wait for some to go berserk and start abusing me again as they did on the last thread. However, don’t shoot the messenger. I am bringing this forward particularly because CASA has refused to “Stop the lie and change the Act” to the words agreed to by the Shadow Minister, Anthony Albanese.

If I were a professional at CASA, I would want to be able to tell the truth rather than live a lie. I would imagine presumably these people have to go home and night and tell their children to be honest, but during the day they have to speak in a completely different way and follow the dishonest ‘groupthink’.

Then again, another section of the Canberra bureaucracy has told Canberrans that their electricity will be 100% from renewables from 2020. I suppose Canberra is the home of dishonesty. What a pity, it is so unnecessary.

[Ascend Charlie]

Perhaps because, after the first engine shutdown, the distance to a safe alternate across the far south Pacific is too long, increasing the chance that the second engine would go on leave?

[Veruka Salt]

Dick,
Engine reliability is only part of the risk analysis. Cargo fire suppression, amongst other things, plays a part.
FYI the 4-eng aircraft in our company are required to comply with ETOPs rules beyond 180 mins flight time from an adequate airfield.
It's not the prospects of a long flight with an engine shutdown that spooks me; more the uncontained cargo fire.
VS.

[On eyre]

I am with you Dick - as the Pantene hair shampoo advert said in the 90’s “ It won’t happen overnight but it will happen” - will be interesting to see how the first airline to be unfortunate enough to suffer this fate handles the whole thing.

[machtuk]

Dick,
Engine reliability is only part of the risk analysis. Cargo fire suppression, amongst other things, plays a part.
FYI the 4-eng aircraft in our company are required to comply with ETOPs rules beyond 180 mins flight time from an adequate airfield.
It's not the prospects of a long flight with an engine shutdown that spooks me; more the uncontained cargo fire.
VS.

Whilst that is of some concern (cargo fire) I wonder how many uncontained cargo fires there have been compared to engine failures if we are going to look at what the risks are for EDOPS? Safety comes at a cost, Airlines look at cost first then safety despite all the hype!

[Who stole my meds]

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.

LATAM fly a 787-9 between Auckland and Santiago and Air New Zealand fly Auckland to Buenos Aires......just saying

[Veruka Salt]

Mach,
Clearly cargo fires occur less frequently than engine failures. However, I would argue the odds of survival are much less. Therefore, in the risk = severity x frequency equation, engine failures are the overiding risk consideration. But I'll take an engine failure any day over cargo fire!
Cheers.

[Squawk7700]

How much, if any, extra power is applied to the working engine in an engine failure scenario to maintain flight to the nearest suitable landing location?

[Lead Balloon]

Perhaps because, after the first engine shutdown, the distance to a safe alternate across the far south Pacific is too long, increasing the chance that the second engine would go on leave?Interesting theory.

How does the good engine 'know' the failed engine has failed?

[A37575]

How much, if any, extra power is applied to the working engine in an engine failure scenario to maintain flight to the nearest suitable landing location?


Can't find it now but I recall from 1976 reading in a a 737 Boeing letter to operators that it is worth considering leaving the live engine at cruise power (rather than advancing to MCT) if drift down terrain clearance is not a factor.
I took the Boeing advice after having to shut down an engine at 33,000 due loss of engine oil contents half way between Nauru and Fiji and drifted down at cruise thrust for next 1.5 hours. Psychologically it felt much more comfortable not touching the live engine than advancing to MCT when there was no need to performance-wise.

[Lead Balloon]

1976? I suspect there have been some technical advances since then.

[Veruka Salt]

Can't find it now but I recall from 1976 reading in a a 737 Boeing letter to operators that it is worth considering leaving the live engine at cruise power (rather than advancing to MCT) if drift down terrain clearance is not a factor.

How much, if any, extra power is applied to the working engine in an engine failure scenario to maintain flight to the nearest suitable landing location?

We select MCT initially to initiate a driftdown (company policy), but then have the choice of other strategies following due consideration if terrain isn't a factor . That (obviously) could be all the way back to idle for diversion to a nearby field. As an aside, drift down ceiling for the A330 is approx FL200 at MTOW, and around FL260 at typical landing weights, so any scenario not requiring flight at those levels (due terrain, lengthy diversion etc) would use less than MCT.

[Squawk7700]

Interesting theory.

How does the good engine 'know' the failed engine has failed?

Because it’s being flogged and pushing along a bloody big aircraft on its own! Isn’t that to an extent, what happened to Wyalla?

[Tankengine]

The most likely cause of both engines failing at the same time is fuel contamination, which would also affect a four engine aircraft.

[umop apisdn]

Isn't the statistical probability of the second engine failing completely independently of the first the same as having a double engine failure in a quad? Surely that would have trouble maintaining altitude as well?

[Lead Balloon]

Because it’s being flogged and pushing along a bloody big aircraft on its own! Isn’t that to an extent, what happened to Wyalla?
No, it's not being flogged. And I'm not sure how defective crankshafts and bad mixture management in a piston engine translates to a jet engine.

But apart from that, I get your point.

[Global Aviator]

https://en.m.wikipedia.org/wiki/List_of_airline_flights_that_required_gliding

[AerocatS2A]

I have recently been told that statistically we are over that time and the safety experts are wondering when such a disaster will happen.

Statistics don’t work that way. An unlikely event doesn’t become “due” just because it hasn’t happened for ages. The chances of two engines failing now are just as unlikely as they were several years ago.

[Mr Approach]

I worked this out on the back of a beer coaster........
Assume that airplane engines operate independently of each other and that at least half of the engines on a plane must operate for the plane to continue flying.
A particular airplane engine fails with a probability of 1/7. which is safer, an airplane with 2 of these engines or a airplane with 4 of these engines

Consider the possible scenarios for the engines with a two engine plane.
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
Disaster for a two engine plane is when both engines fail (1/2 or 1 engine would be OK).
That is case 4 and the probability is 1/49.
..
It works the same for a four engine plane but more outcomes (16 instead of 4).
The probabilities are the same : W(6/7), F(1/7), the denominator now is 7*7*7*7=2401.
..
1.W1*W2*W3*W4=6*6*6*6=1296/2401
2.W1*W2*W3*F4=6*6*6*1=216/2401
3.W1*W2*F3*W4=6*6*1*6=216/2401
4.W1*W2*F3*F4=6*6*1*1=36/2401
5.W1*F2*W3*W4=6*1*6*6=216/2401
6.W1*F2*W3*F4=6*1*6*1=36/2401
7.W1*F2*F3*W4=6*1*1*6=36/2401
8.W1*F2*F3*F4=6*1*1*1=6/2401
9.F1*W2*W3*W4=1*6*6*6=216/2401
10.F1*W2*W3*F4=1*6*6*1=36/2401
11.F1*W2*F3*W4=1*6*1*6=36/2401
12.F1*W2*F3*F4=1*6*1*1=6/2401
13.F1*F2*W3*W4=1*1*6*6=36/2401
14.F1*F2*W3*F4=1*1*6*1=6/2401
15.F1*F2*F3*W4=1*1*1*6=6/2401
16.F1*F2*F3*F4=1*1*1*1=1/2401
.
Disaster for a 4 engine plane is when 3 or more engines fail (2 engines failing is OK).
Look for those cases (3 F or more), they are 8,12,14,15,16.
Their probabilities add,
P(3 or more engines failing)=P(8)+P(12)+P(14)+P(15)+P(16)
P(3 or more)=(6+6+6+6+1)/2401=25/2401
.
For the two engine plane, P(disaster)=1/49=0.0204
For the four engine plane, P(disaster)=25/2401=0.0104
.
Therefore the four engine plane would be a safer bet but we all know that don't we?
By the way the calculation is even better if the plane has six, eight or ten engines...that is where a cost/benefit calculation is then made,
When does the cost of the airfare outweigh the risk that the passengers are willing to take to get to where they are going?

[Dick Smith]

Aerocat. I am shocked. Are you telling me CASA has put lower cost and higher participation levels in front of improving safety?

Of course they do! That is to the powerful! Wouldn’t you then think they would tell the truth about this?

More importantly most passengers have never been informed of the lower level of safety.

[rog747]

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.

[cattletruck]

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.

[PDR1]

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

[ShyTorque]

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.....

[oggers]

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?

[swh]

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.

[tdracer]

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.

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

[OZBUSDRIVER]

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?

[sgenie]

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

[Captain Sherm]

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.

[73qanda]

What about the dependency through mechanical damage ( engine bits severing fuel lines, fly by wire cables etc)?

[Dexta]

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".

[Kelly Slater]

Perhaps it just comes down to "affordable safety".

[tdracer]

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...

[Dick Smith]

Dexta and Kelly ,Exactly what I am getting at!

[cooperplace]

1976? I suspect there have been some technical advances since then.

in the 737??

[Snakecharma]

Dick, while I can sort of see what angle you are going for the reality is that you are pushing **** 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 blasé 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 ****load 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.

[tdracer]

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.

[Lead Balloon]

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.

[Dick Smith]

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!

[Bull at a Gate]

Dick, can you post a link to the expert reports you refer to? Until then, you are wasting my time.

You blindly assert that 4 engines are better than 2, without taking into account the fact that the more engines you have, the greater the likelihood of an uncontained engine failure, with the consequent risk of catastrophic damage to the controllability of the aircraft.

Maybe you are right and maybe you are wrong, but let’s have some evidence please!

[Dick Smith]

I make no such blind claim.
Look at the heading to this thread.

Why not answer the reasonable question?

[LeadSled]

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,
That is Dick's whole point ---- CASA are very selective in their interpretation of S.9A of the Act.
When it suits them, CASA's interpretation of S.9A is that something called "safety" is THE ONLY CONSIDERATION.
This is the untruth that is peddled to the public, as most of us know, the reality is very different.
Otherwise, how can you have, say, an MEL, shouldn't everything be 100% serviceable?? Full stop!! For "safety".
Tootle pip!!

[Ex FSO GRIFFO]

Imagine...….(An 'oldie', but.....)

The 'early' days of 4 engine aircraft across the Atlantic, on a RPT basis, passenger gets an invite to flight deck, (like they used to then...), and after talking to pilot for a short time, asks....
"Capt., what do you think would the minimum number of engines for a risk free 'comfortable' flight across this vast ocean?"
Capt thinks for a while, then responds, "When the FO says to me, 'Capt, we have a problem - Number 16 is losing oil pressure...'
And I reply, "Oh!.. Which side..??"

As told to me troooly…….
Cheers

[Bull at a Gate]

Oh dear Dick,

Of course you are claiming that 4 are safer than 2. Go back and read your original post.

And the question you pose in the title of this thread demonstrates a misunderstanding of statistics.

If all you can do is make provocative statements without even trying to back them up with evidence then what is the point of even trying to engage in a discussion with you?

[LeadSled]

Oh dear Dick,

Of course you are claiming that 4 are safer than 2. Go back and read your original post.

And the question you pose in the title of this thread demonstrates a misunderstanding of statistics.

If all you can do is make provocative statements without even trying to back them up with evidence then what is the point of even trying to engage in a discussion with you?

Bull,
Go back and re-read ##42 and ##43, you are missing Dick's whole point.
Tootle pip!!

[tdracer]

Bull,
Go back and re-read ##42 and ##43, you are missing Dick's whole point.
Tootle pip!!

No, you're missing the point. Dick is implying that, by allowing twin engine ETOPS, they are making air travel less safe. The statistical data simply doesn't back that up.
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!

I see, you can't back up your posts with data, so you resort to insults. Nice....
If you'd bothered to talk to actual certification experts, you'd know that 'safe' is clearly defined in the certification regulations - in short is says if the probability of a catastrophic outcome is less than one in a billion flight hours (i.e. 10-9/hr), it's safe. ETOPS regulations are based on that requirement. Every critical system on the aircraft is certified based on that one in a billion requirement.
Any aviation expert worth their salt would know that. Somehow your experts don't. I guess that's why your experts are anonymous.
You repeatedly imply that ETOPS is somehow less safe, but never actually say it in so many words, then proclaim "I have not made any claim" . You clearly have an agenda - you're not fooling anyone.
You could just as well start a thread that asks 'when will a quad end up in the drink?'. It's clearly an unanswerable rhetorical question. Funny thing about random events, no one seems to know when they will happen.
BTW, as far as my handle and posting anonymously, anyone who really cared could figure out who I am in about five minutes - people who know me immediately recognize it as my nickname. Heck it's on my license plate.

[AerocatS2A]

I make no such blind claim.
Look at the heading to this thread.

Why not answer the reasonable question?
The question is meaningless. Statistical mathematics can’t answer “when?” It can only give probabilities and the probabilities don’t change based on whether something has or hasn’t occurred. The chance of a coin toss coming up heads is 50%, however if you happen to toss 100 tails in a row your chances of the next toss being heads is still 50%. It hasn’t become “due”, there is no “time when heads is going to appear”. Likewise there is no time when “a twin is going to end up in the drink?”

Stop being emotive, provocative, etc. Talk plainly, state what you mean, don’t ask meaningless questions. Debate with integrity. Once you start doing that, a lot more people will give you the time of day here. And for gods sake let go of this fixation you have with anonymity on this website. Some of us like to have some sort of privacy and it has absolutely nothing to do with the value of our opinions.

[Squawk7700]

The smarter part of my brain suggests that regardless of probabilities, each event is mutually exclusive and two failures could absolutely occur on the one flight and that could be just after takeoff, over water or anywhere for that matter.

If you had told me that five 0’s were going to come up one night at Crown Casino on Roulette, I’d never have believed you, but it did happen.

I feel as though the Swiss cheese effect is more likely to cause the twin failure (at different times on the one flight), rather than 2 x compressor blade / actual physical engine failures for example.

[Captain Sherm]

Yep, actual experts please Dick. And that doesn't mean you or GT or BB or other usual suspects.

[Squawk7700]

BTW, as far as my handle and posting anonymously, anyone who really cared could figure out who I am in about five minutes - people who know me immediately recognize it as my nickname. Heck it's on my license plate.

We all know who and what you are... a showboat, who likes the sound of his own engine (or motor as you put it) !

You’re quoting some very small probability figures, but do they include engine shrowds and that type of thing blowing off and damaging the engine causing shutdowns, or by failure, do you mean actual internal turbine failure for example, and does engine failure include hoses blowing off necessitating manual shutdown by the pilots?




Since I retired about 18 months ago, I've been looking to 'reward myself' and buy some sort of 'super car'. As may be guessed from my handle, I'm a big car guy, and I'm especially into the engines - partly an outgrowth of my 40 years as a propulsion engineer at Boeing. Previous examples of my interest in unusual automotive engines have included the original Buick Grand Nation 3.8 liter turbo, four different RX-7 rotaries, and my current 2 liter, 240 HP/8,900 rpm Honda S2000 (some of the racing engines I drove were similarly exotic - including one that I routinely revved to 16k - it sounded wonderful https://www.pprune.org/images/smilies/evil.gif).
Starting shortly before I retired, I lusted for a Ford GT350 Shelby Mustang and it's 5.2 liter, 526 hp, 8k, flat plane 'Voodoo' naturally aspirated V8. Unfortunately I wasn't the only one, and new GT350 Mustangs were selling for ~$15k over the ~$60 list price - something I was unwilling to pay. Then, about six months ago, while getting my Ford van serviced, I walked into the Ford showroom and discovered they had two GT350 Mustangs in-stock, and were only asking for MSRP. WhooHooo! I took one for a test drive - the motor was as fantastic as I expected and it sounded glorious - but the wife objected. She didn't want me to get rid of the S2000 (she really likes that it's a convertible) - and I couldn't justify having both the Shelby Mustang and the S2000. https://www.pprune.org/images/smilies/censored.gif
So, I'd been looking at various other 'super cars' - Austin Martin, Acura NSX, McLaren, etc., but to get into something I really wanted the price kept escalating yet it would still only be like my S2000 - a nice weather car that I'd be able to drive maybe 4 months per year.
Then BMW introduced a new M5. My current daily driver is a 2007 BMW 328xi (AWD) - I love it, and the AWD means I can drive it year round regardless of the weather, the only real down side is it's on the small side for long road trips (the wife doesn't exactly travel light, and we often take our two dogs along). The new M5 is AWD, significantly more room than my 328, very good handling and a twin turbo V8 producing 600 hp and sub 3 second zero to 60 gives it legitimate 'super car' creds, and if I buy an extra set of wheels fitted with proper snow tires it's a legitimate all weather, daily driver car. I've already arranged to sell the 328xi to an in-law, I keep the S2000 so my wife is happy, and I can give that snooty Tesla 'ludicrous mode' driver a scare https://www.pprune.org/images/smilies/thumbs.gifMy biggest complaint is the motor sound is muted by the turbo (yea, I'm seriously into that sound aspect)
The only problem is it'll be ~six months before my M5 arrives...

[Bull at a Gate]

Here is a genuine question: in the last 10 years how many twin engine aircraft have crashed in circumstances where they would not have crashed had they had 4 engines? I can think of a couple of examples involving shutting down the wrong engine but Dick’s beef seems to be more related to mechanical unreliability. So, how many in that category?​​​​

[PDR1]

We all know who and what you are... a showboat, who likes the sound of his own engine (or motor as you put it) !


Don't know who he is, but I am an aeronautical engineer (Chartered Engineer) who has (at various times) focused on both airworthiness certification and supportability engineering - a field that includes reliability and maintainability engineering (as it happens I have a masters degree in supportability engineering). I have been involved in the process of certifying aeroplanes many times, including undertaking the fault-tree anaylsis that determines the probability of single and multiple events leading to undesirable end-effects like death, serious injury and significant damage (this is a large chunk of the statistical process people have mentioned above). Each case is different, but these days it is a very common finding that (once you strip out the common-mode causes like fuel feed failure/leaks/contamination, maintenance-induced failures etc) the probability of a double-engine failure is much, MUCH lower than the probability of other events which would bring down a particular aeroplane. This is because modern engines have become so reliable and because they are much better instrumented with prognostic health monitoring systems so that a potyential failure is mitigated before it causes a disaster. And yes, I have seen cases where adding additional engines INCREASES the probability of aircraft loss due to risks like engine fractricide and uncontained fire/burst etc.

As a result in most cases it is simply more rational to spend effort/money on eliminating failure causes that are more probable than it is burdening aircraft with physical and financial features relating to much less likely events.

Sorry to contradict you on this Dick, because it's something you clearly have strong and passionate views on. But I am labouring under the distinct disadvantage of actually knowing what I'm talking about.

PDR

[George Glass]

PDR1, With all due respect, you dont understand. You are dealing with the tin-foil hat brigade. Your professional qualifications are merely the source of suspicion and contempt. Much more comforting for the lumpen internet dross to be reassured that their grievances are real and evidence to the contrary is proof of a conspiracy.

[LeadSled]

No, you're missing the point. Dick is implying that, by allowing twin engine ETOPS, they are making air travel less safe. The statistical data simply doesn't back that up.
.

tdracer,
You should re-read Dick's very first post, that started this thread.
And I have no idea who you are.
Tootle pip!!
PS: I do know something about the subject, having been closely involved in the introductions of EROPS in Australia --- including much discussion on the statistical issues, and the reasons for the engineering mods. that made an ordinary B767 an ER. And the problems we experienced.

[cattletruck]

Don't know who he is

All I know is he worked at Boeing, designed or fitting engines to their contraptions, and is now earning a well deserved retirement. His posts are often well informed and full of technical engineering porn.

The leading edge in manufacturing (and often it's the aviation industry) are constantly breaking new barriers, which includes operating huge CNC milling machines, 3D printing, growing structures in crystallite form, new composite materials, bonding techniques, computer assisted modelling... the list goes on - it's now a young man's game (under expert guidance of course).

[B772]

In the late 1980's I attended a Boeing conference where a briefing on the planned B777 was given. At the time I was not too concerned about the A310 and the A300 as they were regarded as regional operation aircraft. (The early Emirates services to MEL were operated by the A310 to/from SIN) Likewise the B757 and B767 whilst longer range were not capable of trans pacific operations (The B767-200ER was capable).

During the B777 presentation it was obvious Boeing were proceeding at break neck speed to introduce the go anywhere B777. Most pilots at the presentation where aghast at the prospect of a B777 being approved for say LAX-AKL and LAX-SYD. I was concerned about the prospect of up to 200 minutes nail biting on a single engine and the resultant engine bearing damage. (When a heavy twin suffers a shutdown both engines are usually replaced)

I suggested the B777 could have a CFM56 engine in the tail and be regarded as a tri-jet. The CFM56 would be used for take-off and shutdown at the top of climb. The engine could be shuttered for aerodynamic purposes when not required. In the event of a shutdown or worse the CFM would be fired up and provide centre line thrust and possibly electrical power and pressurisation. My suggestion was shot down by the Boeing attendees as being too expensive and adding weight to the aircraft.

[Australopithecus]

In the late 1980's...

...I was concerned about the prospect of up to 200 minutes nail biting on a single engine and the resultant engine bearing damage. (When a heavy twin suffers a shutdown both engines are usually replaced)

I suggested the B777 could have a CFM56 engine in the tail and be regarded as a tri-jet.... My suggestion was shot down by the Boeing attendees as being too expensive and adding weight to the aircraft.

What is this bearing damage of which you speak? In a turbojet engine? Its called Maximum Continuous Thrust for a reason, and the rotating elements of the bearing are subjected to slightly higher velocities but still within their design envelope.

Regarding your aux engine idea: I have heard at the bar: “The only reason I prefer four engines is that there are no five-engined planes” . I guess time has shown that our earlier luddite outrage was misplaced.

Thinking back to the original loooong range aircraft, they went from ten engines (B-36) to eight (B-52). All of that was dictated by take-off performance. Their mission hasn’t changed, yet the new bombers are twins.

Engines share more than just fuel. They share air, containing freezing precip, ice crystals, hail, ash, birds, non-TCAS traffic. They also share oil and maintenance. They share manufacturer, including flaws, bad metallurgy, bad design. They also share a common parts stream which may be open to counterfeits. They also share operators, including people who forget anti-icing, screw up the fuel scheduling, etc. All of the foregoing is true regardless of the number of powerplants.

Oh yeah....engines also share the duties of carrying around people with evil intent, pallets of lithium batteries and flights planned through war zones. The entire enterprise is based on odds which I reckon are about 9 to 5 against.

[PDR1]

Of course the B777 has now been in service for 24 years, with most of that time having a large number of aircraft flying at very high utilisation rates, racking up the flying hours. In that time I count 3 ground fires due to engine failures, one ground fire on refuelling, 2 major electrical faults (one on the ground, 1 in the air), one crash due to iced fuel filters, one lost to a missile, one in-flight crew death and two lost due to crew actions (if you include MH370, which I tend to). There isn't a single one of these where adding a third (let alone a fourth) engine would have changed the outcome, but if the weight/cost/effort were deemed necessary sacrifices there could have been significant benefit from more extensive fire detection/surpression capabilities. There might also be tangible benefit in beefing up the zonal inspections to spot electrical chafing. But on the reliability performance from its first quarter-century there would be more justification in adding a third (or fourth) pilot than extra engines, so those who shot you down were almost certainly justified in doing so.

But you are also talking about stanby redundancy rather than active redundancy - this is a whole different skillet of sardines. A 3/4 engined aeroplane has "active" redundancy in that all the engines are rrunning but the system can still perform if one or more stop. But "standby" redundancy involves carrying a spare engine that would only be foired up in an emergency, which means you have toi consider the probability that this engine will work WHEN YOU NEED IT, rather than whether a working engine will fail shortly after a fraternal failure. The probability sums here are very different. If you do the maths you usually find that a standby system has to be at least eight times more reliable than the active system to provide any significant reduction in hazard rate. This becomes even more extreme with complex heat machines like gas turbines because they characteristically tend to fail the most on start-up (probability of failure of a gas turbine on start up is five times greater than probability of failure during periods of cruise power). So you were probably shot down because the engineers present could show that your proposition made overall reliability worse rather than better, even if just due to the increased parts count.

PDR

[Dick Smith]

It’s clear that the prime reason for the move from 4 engined to two engined is not to improve safety but to improve participation levels and airline profits- and it has clearly worked.

Thanks for all the written evidence I require to show that.

CASA is clearly not complying with “the lie” in the act!

One day the act act will be changed to reflect the truth.

[Check_Thrust]

I'm sorry Dick, where in the replies that you have received does it clearly state that? What is the written evidence?

I understand your end game reference the Act but I don't really see evidence in this thread that supports your position.

[Jetstream67]

Like so many safety issues we will only really know the statistical answer looking back.

The move to twin engines was paralleled by increased reliability of engines and redundancy of systems and more obsessive maintenance processes and the flight crews desire to arrive safely too on failure of engine #1. The sum of those factors is still being calculated

The Customer is a realist: They like cheap flights and if the chances of making it to a safe landing are increasing vs last time they don't care much about the reliability of the most reliable parts . . most are more scared of a nut-case fellow passenger

[tdracer]

It’s clear that the prime reason for the move from 4 engined to two engined is not to improve safety but to improve participation levels and airline profits- and it has clearly worked.

Thanks for all the written evidence I require to show that.

CASA is clearly not complying with “the lie” in the act!

One day the act act will be changed to reflect the truth.

And the agenda is revealed :ugh:
Would you mind sharing some of the "written evidence" supporting your position that quads are more safe than twins? I haven't seen any - on this thread or anywhere else.
On the other hand, there is a whole bunch of data that says twins are safer than quads. For example (numbers as of 2016):
The most common quad in service over the last 30 years is the 747-400 - fatal hull loss rate 0.49 (the older -1/2/300 model 747s are quite a bit worse at 1.46)
By comparison, the aircraft that have largely replaced the 747 on the long over water routes are the 767, 777, and A330. Their fatal hull loss rates:
767 - 0.10
777 - 0.20
A330 - 0.21
All substantially better than 747-400. As are the hull lost rates for the 737NG, 757, and A320 series.
Granted, the A380 rate is currently zero - no fatal hull loss events -but it's a statistically small fleet, however the statistically larger 787 fleet is also at zero (as is the A350).
So I ask again, please share your data that proves twins are less safe? Or will you simply keep repeating your assertion and hope that if you repeat it enough times people will assume it's true?

Oh Squawk - you might want to know that resorting to personal insults is generally considered evidence you're loosing the debate.

[LeadSled]

Like so many safety issues we will only really know the statistical answer looking back.

The move to twin engines was paralleled by increased reliability of engines and redundancy of systems and more obsessive maintenance processes and the flight crews desire to arrive safely too on failure of engine #1. The sum of those factors is still being calculated

The Customer is a realist: They like cheap flights and if the chances of making it to a safe landing are increasing vs last time they don't care much about the reliability of the most reliable parts . . most are more scared of a nut-case fellow passenger

Folks,
One thing I can say without doubt, because I was in the middle of it --- when EROPS (ETOPS/EDTO) was first established in Australia and NZ (and bear in mind no European nation allowed it for years after --- long range twins were "not safe") perhaps the statistics were not as sophisticated as now (after all, there was no huge body of statistics for big twins) but one thing is for certain!!

No supporters of the changes proposed, and those involved in the regulatory approvals (FAA, whatever CASA was then -CAA?, Boeing, P&W and GE, AIPA, QF etc.) considered big twins "safer" or "as safe" as a B747, but the risk of a multiple engine failure was ALARP- As Low As Reasonably Practicable, and that assessed residual risk was seen as acceptable.

Don't forget --- quite properly, in my opinion, many engine failures were excluded from the calculations --- fundamentally any engine failure not in the EROPS phase of the flight. Failures on takeoff, bird-strikes etc did not count.

Increased concern about hold fires and Class D compartments falling out of favour was years down the track, as were lithium batteries, and, if I recall correctly, the very first edition of AS/NZ 4360, Risk Management

Other system redundancies were carefully considered (the B767 has better electrical redundancy than the B747) --- but the "biggie" was engine failure) and aircraft modified compared to a non-ER B767, and it was all about the B757/767, because Airbus didn't want to know, because JAA/UK CAA etc., and all the European pilot unions said NO!!. ITS NOT SAFE!! I don't remember the exact timescale, but the A310, the first Airbus so certified was quite a few years after Boeing.

So Dick's basic proposition is correct, in the genesis of EROPS/ETOPS/EDTO, all accepted (whether it was right or wrong) that long range twins were not "as safe" as a three or four engine aircraft, but they were "safe enough" (my words)--- and "absolute safety", "safety is our first priority" and the present CASA selectively preferred interpretation of S.9A of the Act did not get a look-in.

And Dick's proposition that the Act should be amended, as agreed by Barnaby and Albo, as Minister and Shadow Minister, remains a necessary change, has been a necessary change since 1998, 20 years --- without which we will not see proper application of risk management principles across the board in aviation in Australia --- it will be confined to those with the commercial power.

Tootle pip!!

[tdracer]

So Dick's basic proposition is correct, in the genesis of EROPS/ETOPS/EDTO, all accepted (whether it was right or wrong) that long range twins were not "as safe" as a three or four engine aircraft, but they were "safe enough" --- and "absolute safety", "safety is our first priority" and the present CASA selectively preferred interpretation of S.9A of the Act did not get a look-in.
Perhaps that was true 30 years ago in Australia, I'm not in a position to know. But I was involved in the development of EROPS/ETOPS rules with the FAA in that same time frame. No such provision was made about 'safe enough' - either it's safe (per the one in a billion requirement I posted earlier) - or it's not safe - in which case it's not certifiable. That some groups objected is immaterial - that's an emotional response, not a technical response (not unlike the two crew/three crew flight deck debate)
EROPS/ETOPS rules were developed using technical statistical methods - the same statistical methods used for showing every other critical system on the aircraft is safe. It's also used for an "Equivalent Level of Safety" (ELOS) - when a new design doesn't meet the letter of the regulation but meets the intent of the regulation the regulators can grant an ELOS finding (ELOS was heavily used when EICAS was incorporated to replace all those flight deck lights and dials - and was needed when Boeing incorporated the thrust reverser 3rd lock after Lauda - 25.939 says a deployment in flight must be controllable but with big fan engines that's no longer practical, so Boeing was able to obtain an ELOS by showing the 3rd lock was effective in making sure an in-flight deployment wouldn't happen).
Further, IIRC, while Qantas was an early adopter of EROPS (for flying over the Australian outback), Australia's initial EROPS rules were based on the already existing FAA EROPS rules - rules that had already shown to be just as safe as a quad.
Besides, this whole crusade overlooks a very basic fact. As per my earlier post, current ETOPS twins are statically meaningfully safer than the quads and tri-jets they replaced. By that metric, allowing ETOPS has actually made flying safer and hence saved lives.

[Dick Smith]

That “ one in a billion” requirement sounds to me that the standard does not call for absolute safety.

It looks as as if there are compromises made for affordability reasons.

That is in in some cases CASA and regulators throughout the world put the ultimate cost of safety improvements as the most important consideration.

Just a fact of of life that is admitted in other countries and reflected in legislation.

But not in Canberra. They have “ safety” as the most important consideration- more important in all cases than cost.

Why they live this lie is behind me.

In in the meantime with the “one in a billion” parameter when is it likely that a twin will end up in the ocean?

[Dick Smith]

I note this paragraph from the article “Engine-failure 777 busts ETOPS limit (https://www.flightglobal.com/news/articles/engine-failure-777-busts-etops-limit-163284/)”

“The FAA at present is working in co-operation with US industry body the Aviation Rulemaking Advisory Committee to draw up a new set of standards for long-range aircraft regardless of the number of engines they have, possibly taking modern twins into the 240min ETOPS range and beyond.”

It looks as if since then the rules are simply re-written to allow twin engine aircraft to be used on routes where it is obvious that a four engine aircraft of a similar production date and safety features would be safer.

[Snakecharma]

Dick, the 180 minutes in the article you quote is a planning issue only - planned at up to 180 mins from an appropriate diversion field BUT the pilot in command does not need to fly at the speeds which are used to calculate that 180 minute distance.

So conceivably any number of aircraft schlepping across the Pacific today could quite easily take longer than their diversion time (be it 60, 120, 180, 240, 330, 370 minutes)

I note the A350 has been certified for ETOPS 370 - 6hrs and 10 minutes - but these distances are necessarily derived using a specific speed schedule against the necessary time, so there is no obligation on the crew to fly the speeds used to calculate the ETOPS range rings

[tdracer]

That “ one in a billion” requirement sounds to me that the standard does not call for absolute safety.



No, it is an acknowledgement that - in the real world - "absolute safety" is a myth. Absolute safety simply doesn't exist - particularly in a complex system such as a commercial jetliner.

In in the meantime with the “one in a billion” parameter when is it likely that a twin will end up in the ocean?
Well, at least one 777 has in fact ended up in the ocean - MH370. Of course, based on what's currently known about MH370 the number of engines was immaterial.
As for the rest of your question, all it demonstrates is your lack of understanding of statistics.
BTW, still waiting for you to provide data to back up your claim that quads are safer than twins on long over water routes.

[LeadSled]

Further, IIRC, while Qantas was an early adopter of EROPS (for flying over the Australian outback), Australia's initial EROPS rules were based on the already existing FAA EROPS rules - rules that had already shown to be just as safe as a quad.
.
tdracer,
As you admitted, you were not involved in the development of the Australian (and NZ) rules, and it shows.

EROPS in Australia had nothing to do with the "outback', there was no shortage of places you could put a B767. ( or an early B737, A300 or.DC-9 --- none ever ER)

And everything to do with a network around the western Pacific and SE Asia.

AND, if you had any knowledge of those original AU rules (versus the FAA's, which were developed in an atmosphere of universal pilot union opposition, and resultant political lobbying, and luke warm, at best, FAA support) they were substantially different to the FAA original rules, that were "intended" to make trans-Atlantic EROPS operations as close to impossible as possible. And, if my memory serves me correctly, AU in operation before the US rules. Certainly, Qantas and Air New Zealand conducted something like 80% of EROPS operations in the first three or so years of the "new rules". --- refer the Boeing library.

And a roaring operational and commercial success it was!! Nice to be leader, and not followers, just occasionally. The only case similar I can thing of was FANS-1..

Just one example, AU v. FAA, that I remember --- at no stage did we have to plan for engine out depressurized 10,000 ft diversion in icing conditions. Our rules were really quite practical and common sense --- and said practical common sense had as much influence on the final rules as statistical justification.

And another example, the Captain in the AU rules ( unusual for Australia) had much greater freedom of action, once airborne, than under original FAA rules.

As a final comment, once you get to such low rates of adverse occurrences as the airlines now achieve, ALL occurrences are individual, one interpretation, valid in theory, is that there are not enough occurrences to draw statistically valid conclusions about failure patterns in (now) EDTO --- hence being able to certify a new type "out of the box". With most ICAO states close to the ICAO SARPS, the aircraft performance has developed to the degree that the now more restrictive (compared to AU original) rules have a very limited operational/commercial impact.

Tootle pip!!

PS: Are you aware that there are a number of risk levels used across the board in aviation regulation (except, generally speaking, in Australia) , not one single one to define "safe/unsafe", as you suggest?

[tdracer]

PS: Are you aware that there are a number of risk levels used across the board in aviation regulation (except, generally speaking, in Australia) , not one single one to define "safe", as you suggest?
I presume you're referring to Minor, Major, Hazardous, and Catastrophic - with associated allowable probabilities of 10-3, 10-5, 10-7, and 10-9/hr, respectively. You are correct that 'safe' is not referred to in so many words, however it's commonly stated that if a system can meet the 10-9/requirement, then it's considered safe and you don't even need to address if the failure is Hazardous or Catastrophic.
The original FAA EROPS requirements were finalized in 1985 - and were soon used across the north Atlantic (granted, it's possible to fly across the north Atlantic using a 60 minute diversion using less than optimal routing - some operators chose to remain with 60 minutes or a strange pre-EROPS 90 minute 'exception' rather than jump through the hoops for full EROPS). I certainly don't remember the early rules as making " trans-Atlantic EROPS operations as close to impossible as possible" - although they were rather restrictive.

[tdracer]

What do they call those operations since they are not ETOPS?

Extended Diversion Time Operations - EDTO. EDTO applies to all passenger aircraft - including quads and tri-jets - starting roughly five years ago (cargo quads and tri-jets are exempted from EDTO, cargo twins do need to meet it).

[puff]

As mentioned by tdracer, since 2015 in our area of the world at least, ETOPS basically doesn't exist, and is now EDTO. The CASA CAAP about it all is listed below.

EDTO - Civil Aviation Safety Authority (https://www.casa.gov.au/file/105056/download?token=iwdq6K97)