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ANZ gets approved for 330 minute ETOPS

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ANZ gets approved for 330 minute ETOPS

Old 8th Dec 2015, 09:45
  #41 (permalink)  
 
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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.
I was boarding a flight from Sydney to Los Angeles a few years ago, when a fellow traveller stowing her overhead luggage, announced to all around that she had once survived a fatal plane crash therefore we were all safe a statistically, it was virtually impossible that she would be involved in another one!

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!
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Old 8th Dec 2015, 15:51
  #42 (permalink)  
 
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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.
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Old 8th Dec 2015, 17:40
  #43 (permalink)  
 
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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.
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Old 8th Dec 2015, 19:02
  #44 (permalink)  
 
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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!
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Old 8th Dec 2015, 19:03
  #45 (permalink)  
 
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Do Lloyd's of London consider ETOPS a higher risk than 3 or 4-engine trans-oceanic ops? If so, by how much?
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Old 8th Dec 2015, 20:01
  #46 (permalink)  
 
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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.
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Old 8th Dec 2015, 20:18
  #47 (permalink)  
 
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Originally Posted by philbky
wanabee777, but it didn't make LHR, it had to divert to MAN
Well...

You gotta give 'em an "A" for effort.
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Old 8th Dec 2015, 21:19
  #48 (permalink)  
 
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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.
Yes, it is, even if one assumes engine failures are "coupled" it probably means that all will fail instead of 3. Either engines never fail together, meaning likely 1 will fail. Or they do fail together meaning 4 will fail. That 2 or 3 would fail seems highly unlikely. Especially 3? 2 is possible if, say, some part that serves one side of the airplane breaks.

Also, external forces of course means more than one engine might fail. Such as ash or birds or (multiple) missiles.
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Old 9th Dec 2015, 08:41
  #49 (permalink)  
 
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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.)
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Old 9th Dec 2015, 09:50
  #50 (permalink)  
 
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rob-ginger said
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.
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.
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Old 9th Dec 2015, 14:54
  #51 (permalink)  
 
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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.
For General Aviation maybe, but not for commercial airline flights, not by a long shot.

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.
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Old 9th Dec 2015, 15:38
  #52 (permalink)  
 
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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.
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Old 11th Dec 2015, 07:30
  #53 (permalink)  
 
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Originally Posted by peekay4 View Post
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.
Indeed - all else being equal (which it never is) if you increase the number of engines you increase the probability of experiencing an engine failure. With a sufficiently large number of engines - the probability of at least one engine failing approaches gets close to 100%. The only way to reduce the probability of an engine failure to zero is to not have any engines
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Old 11th Dec 2015, 13:04
  #54 (permalink)  
 
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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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Old 11th Dec 2015, 18:56
  #55 (permalink)  
 
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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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Old 13th Dec 2015, 16:56
  #56 (permalink)  
 
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Philbky

The BA 747 diverted to Man due fuel system mismanagement by crew.
Plenty of fuel left for LHR.
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Old 14th Dec 2015, 03:42
  #57 (permalink)  
 
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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.
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Old 15th Dec 2015, 16:23
  #58 (permalink)  
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No Fly Zone
Are the long haul carriers so hungry for cash that they will risk 350 - 600 souls simply to keep the cash flowing.
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.
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Old 15th Dec 2015, 16:33
  #59 (permalink)  
 
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Four donkeys did not help AF 447.
It only had two (AB 330).

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.
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Old 15th Dec 2015, 17:03
  #60 (permalink)  
 
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"IMNHO, 330/5.5 hour ETOPS is stretching the otherwise excellent idea a bit too far. "

Well, why is 330 minutes too far? Why was 300 minutes not too far? 180?

What would make it too far is neglecting to fully account for the failure modes and probabilities, mitigations, redundancies and so forth. If anything, the manufacturers and regulating authorities now have more certification experience and service history to go on than ever. With a properly computed aircraft performance, fuel load, plus the means to provide adequate electrical power for the required amount of time the airplane should be capable of reaching the planned diversion runway. The availability of the diversion runway, weather conditions and so forth are certainly challenges and the dispatcher must keep a wary and vigilant eye on them.
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