ANZ gets approved for 330 minute ETOPS
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It started with an assertion that if you have 4 engines, an engine failure is twice as likely as with 2-engines; and so on. Amusing up to a point, but rubbish.
This seemed to give great comfort to the person sitting next to me, a nervous flyer, and I didn't have the heart to tell him that chances of the plane crashing was exactly the same, whether this woman was on board or not!
"Well it's easy to show mathematically that the probability of at least one engine failing is greater when you have 4-engines vs. 2-engines. But it's not double."
But there is, mathematically at least, a significantly lower probability of a return with only a single engine operating with a 4-engine jet.
But there is, mathematically at least, a significantly lower probability of a return with only a single engine operating with a 4-engine jet.
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[Just concerned and a bit more knowledgeable than average SLF here, long time passionate reader, few posts as my profile says, sorry to intrude, kindly bear with me]
The subject of the probability of a second engine failure has been touched at the beginning of this thread, but not discussed much later.
I have a question here: of course the maths say that it's exactly as probable as the first failure, but what do the engineers say? There must be some extra stress put on the remaining engine even if the flight level is decreased, isn't it?
I'd assume that the remaining engine must be running at a higher thrust than usual for up to 5 hours and a half, isn't this changing the odds a little bit? Pushing things even further: what about prolonged asymmetrical thrust? isn't this possibly altering the airflow to the engine and causing some different forces to apply? (if not to the engine, to the pylon?)
Side note: I suffer from mild fear of flying (hence PPrune as my therapy
), and I usually feel a lot safer aboard a quad. The posts above really are food for thought!
The subject of the probability of a second engine failure has been touched at the beginning of this thread, but not discussed much later.
I have a question here: of course the maths say that it's exactly as probable as the first failure, but what do the engineers say? There must be some extra stress put on the remaining engine even if the flight level is decreased, isn't it?
I'd assume that the remaining engine must be running at a higher thrust than usual for up to 5 hours and a half, isn't this changing the odds a little bit? Pushing things even further: what about prolonged asymmetrical thrust? isn't this possibly altering the airflow to the engine and causing some different forces to apply? (if not to the engine, to the pylon?)
Side note: I suffer from mild fear of flying (hence PPrune as my therapy
), and I usually feel a lot safer aboard a quad. The posts above really are food for thought!
Alain, Try not to confuse a piston engine at MCT with a turbine at MCT.
Running a turbine at MCT does not decrease reliability or increase the likely hood of an engine failure. It just increases the cost of overhaul and reduces the time on wing due usually due to reduced EGT margin caused by the higher temp and RPM.
Generally for a given engine, more thrust = reduced life = more cost which is why operators try to keep thrust use to as low as possible.
Engines such as the CF6 (LM2500 for example) run for hundreds of thousands of hours at maximum power in electrical power generations.
Running a turbine at MCT does not decrease reliability or increase the likely hood of an engine failure. It just increases the cost of overhaul and reduces the time on wing due usually due to reduced EGT margin caused by the higher temp and RPM.
Generally for a given engine, more thrust = reduced life = more cost which is why operators try to keep thrust use to as low as possible.
Engines such as the CF6 (LM2500 for example) run for hundreds of thousands of hours at maximum power in electrical power generations.
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"Well it's easy to show mathematically that the probability of at least one engine failing is greater when you have 4-engines vs. 2-engines. But it's not double."
But there is, mathematically at least, a significantly lower probability of a return with only a single engine operating with a 4-engine jet.
But there is, mathematically at least, a significantly lower probability of a return with only a single engine operating with a 4-engine jet.
Also, external forces of course means more than one engine might fail. Such as ash or birds or (multiple) missiles.
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Alain, If you're nervous about flying and you think more engines is safer then DON'T read this:
https://en.wikipedia.org/wiki/Eastern_Air_Lines_Flight_855
..where all three engines failed because of a "common mode" problem, namely a maintenance engineer's mistake.
But the silly thing is most of us drive to and from the airport, and you're MUCH more likely to get killed in a car accident. (Some friends with young children, when traveling without them, used to catch the same taxi to the airport then get on separate flights until they realised how pointless that was.)
https://en.wikipedia.org/wiki/Eastern_Air_Lines_Flight_855
..where all three engines failed because of a "common mode" problem, namely a maintenance engineer's mistake.
But the silly thing is most of us drive to and from the airport, and you're MUCH more likely to get killed in a car accident. (Some friends with young children, when traveling without them, used to catch the same taxi to the airport then get on separate flights until they realised how pointless that was.)
rob-ginger said
Not necessarily. It depends whether you measure risk per kilometer, per hour or per journey.
The reason Air Travel is generally seen as much safer is that most statistics quote deaths per passenger kilometer, which is favourable to large vehicles travelling long distances. Even the space shuttle doesn't do bad on that measure despite two fatal accidents in only a few dozen flights.
...but if you have an average car journey to the airport, followed by an average flight - the riskiest part is the flight.
But the silly thing is most of us drive to and from the airport, and you're MUCH more likely to get killed in a car accident.
The reason Air Travel is generally seen as much safer is that most statistics quote deaths per passenger kilometer, which is favourable to large vehicles travelling long distances. Even the space shuttle doesn't do bad on that measure despite two fatal accidents in only a few dozen flights.
...but if you have an average car journey to the airport, followed by an average flight - the riskiest part is the flight.
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..but if you have an average car journey to the airport, followed by an average flight - the riskiest part is the flight.
E.g., there's been no passenger fatalities due to a US airline accident since Feb, 2009. That's 6+ years of zero fatal accidents.
For comparison, in the same time period about 250,000 (!) people died in US car crashes, an average of 37,000 deaths per year. No matter how you slice it (per trip, per travelled mile, per hour, etc.), the fatal accident rate for cars is going to be > 0.
Statitical analyses
For a bit more background on early ETOPs discussions see the latter part of post #26 in Tech Log (http://www.pprune.org/9180842-post26.html) in the thread on "savings from fewer engines".
I won't repeat it all here but in the 1982 ICAO ETOPS study group, the statistical data put forward by "the industry" (Boeing/Airbus/IATA) was very flaky. They did not want many issues that result in engines and systems not delivering their full performance to be counted. They were strongly opposed by IFALPA and others, which led to their opening position being rejected and the much more detailed rules that today allow very long range diversions.
I won't repeat it all here but in the 1982 ICAO ETOPS study group, the statistical data put forward by "the industry" (Boeing/Airbus/IATA) was very flaky. They did not want many issues that result in engines and systems not delivering their full performance to be counted. They were strongly opposed by IFALPA and others, which led to their opening position being rejected and the much more detailed rules that today allow very long range diversions.
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Yes, well, if we are going to be silly ; Boeing were asked why they opted for four, rather than , say, three or even two engines for the 747 design. They replied ; "We couldn't find anywhere to place the fifth !! !
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Engine No. 2 1/2
In the seventies, the airline I worked for managed to occasionally install a 5th engine on 747s. OK, it seemed to use a fair bit of cargo-straps round the fan blades but - there it was - 'number 2 and a half'
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Stretched Too Far?
IMNHO, 330/5.5 hour ETOPS is stretching the otherwise excellent idea a bit too far. Since virtually all ETOPS qualified airplanes and flight plans include a very long over-water segment, with few or no options, I have to believe that a few carriers are pushing the limits a bit too far. Perhaps the principal fault is limited to one engine. perhaps there is collateral damage that the crew does not know about or that in time may affect the other, Only Remaining engine. Some details they know and some they cannot know.
Are the long haul carriers so hungry for cash that they will risk 350 - 600 souls simply to keep the cash flowing. (In a few cases, the weight of the printed currency, alone, carried as 'freight' can impact the airplane's range. A few carry A LOT!!)
In addition, only a fool plays the statistical games; just because that 1:1 Million event has occurred, does NOT mean that another one, similar or different, cannot occur and even on the same flight. In fact, after one even has happened, the odds of a second one actually increase. Reasonable ETOPS times are a good thing, but they have become excessive. Let's curb those profits a bit and focus on safety. Every flight on every route.
Are the long haul carriers so hungry for cash that they will risk 350 - 600 souls simply to keep the cash flowing. (In a few cases, the weight of the printed currency, alone, carried as 'freight' can impact the airplane's range. A few carry A LOT!!)
In addition, only a fool plays the statistical games; just because that 1:1 Million event has occurred, does NOT mean that another one, similar or different, cannot occur and even on the same flight. In fact, after one even has happened, the odds of a second one actually increase. Reasonable ETOPS times are a good thing, but they have become excessive. Let's curb those profits a bit and focus on safety. Every flight on every route.
Paxing All Over The World
No Fly Zone
Yes.
Corporates will always risk their long term reputation for short term gain. Mainly because, when the risk finally bites - the men who thought it up are retired and on the golf course. They can then blame the next generation for having messed up their brilliant work.
This book is often recommended in these forums and it is very good:
The Tombstone Imperative: The Truth about Air Safety
Book by Andrew Weir
For me (paxing for 50 years now) 330 is too long. I agree that the journey to the airport is hazadous but I will not boost their bonus in this way. I am well aware that the 777 has paved the way but (as given by others) it is the unknown, the unexpected that trips you up. It is the increasing complexity of systems and human's understanding and interaction with them. Four donkeys did not help AF 447.
You pays your money and you takes your choice.
Are the long haul carriers so hungry for cash that they will risk 350 - 600 souls simply to keep the cash flowing.
Corporates will always risk their long term reputation for short term gain. Mainly because, when the risk finally bites - the men who thought it up are retired and on the golf course. They can then blame the next generation for having messed up their brilliant work.
This book is often recommended in these forums and it is very good:
The Tombstone Imperative: The Truth about Air Safety
Book by Andrew Weir
For me (paxing for 50 years now) 330 is too long. I agree that the journey to the airport is hazadous but I will not boost their bonus in this way. I am well aware that the 777 has paved the way but (as given by others) it is the unknown, the unexpected that trips you up. It is the increasing complexity of systems and human's understanding and interaction with them. Four donkeys did not help AF 447.
You pays your money and you takes your choice.
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Four donkeys did not help AF 447.
Other than that, I'm with you on that one. 330 is a tad too long for my taste, even more so given the route they intend to use this on.