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A 787 that is out one engine will put extra load on the remaining engine, if that one has gone through a similar life as the one that just dropped bits all over

A 787 that is out one engine will put extra load on the remaining engine, if that one has gone through a similar life as the one that just dropped bits all over the place I'd not wager on the remaining one being as safe as when it was last inspected. That's a lot of eggs in one basket. That's why there are restrictions on which RR engines can be put in a 787 as well as a reduction in the ETOPS certification. There've been a few revisions to the Trent, and putting two of the more "unfixed" ones on one airframe is verboten.

hammock 7y ago
That's a nice solution now that we know the engines need fixing. What about when they were first released? Are planes required to have one old-reliable engine?
- kijin 7y ago
  That's what testing is for, although I'm not sure how much I'd like to trust Boeing and FAA with testing these days.
- inferiorhuman 7y ago
  What about when they were first released? If memory serves Rolls placed the blame on the initial problems with the Trent 1000 on air quality in SE Asia (high sulfur content specifically). Which is to say, I don't get the impression that certification was done sloppily. Are planes required to have one old-reliable engine? Reliability is (theoretically) improved. From following threads on a.net and pprune it seems like Norwegian actually demanded new engines instead of repaired older ones. Personally, I'm of the mindset that engines are fantastically safe these days. Piston engines were notoriously unreliable, and even older jet engines were deemed unreliable enough to require more than two for oversea crossings. Look back to when the L-1011 was introduced. It was late due to problems with the Rolls Royce RB-211 (predecessor to the Trent family). Even after the L-1011 began service in-flight shutdowns were pretty common. What we're seeing with the 787 is seemingly less frequent and has provoked a stronger reaction. Of course GE (CFM) isn't immune to problems either and if you look back over their history they've had a few nasty problems including that fairly recent Southwest flight with a passenger fatality.
  - wahern 7y ago
    They are much more reliable, but also much more costly to build and maintain. There was an argument that the A380 wasn't less fuel efficient simply because it had four engines. When you only have two engines they need to be much more reliable, have much higher peak output, and the costs of maintenance are greater. Whereas when you have four engines each engine is cheaper to build, can have more efficient power profiles, and are generally cheaper to maintain. All-in-all it's mostly a wash in terms of cost efficiency. The argument goes that what killed the A380 wasn't having 4 engines, but having 4 old engines. All the newer planes have engines at least 1 if not 2 generations newer. Notably, the A380 wasn't cancelled until it became crystal clear that engine manufacturers weren't going to invest in redesigned engines. That's when the Emirates order fell through. While their year long dance with Airbus over pricing is what got the most press, it was the backroom negotiations with Rolls Royce that controlled whether the A380 remained cost effective.
    - salawat 7y ago
      I thought A380 was doomed because of lack of configurability for a freight option, and the fact that some narrow bodies were starting to eat it's lunch as direct flights started to become more common instead of hub and spoke. What you've posted though seems way more plausible though I've gotta admit.
      - wahern 7y ago
        There are many reasons why the A380 didn't have a large market, which would indirectly contribute to its cost effectiveness. But there's a dominant, ELI5 narrative that says that the A380 was intrinsically uncompetitive because 4 engined planes couldn't be as fuel efficient as 2 engined planes. Maybe that's true, but I found the counter argument interesting and persuasive. I think this is the article I originally read, https://leehamnews.com/2018/12/13/has-the-a380-worse-economics-than-the-777-9-or-a350-1000/#comments https://leehamnews.com/2018/12/13/has-the-a380-worse-economi... but it's paywalled. Here's an older article with similar points, https://leehamnews.com/2015/12/11/bjorns-corner-twins-or-quads/ https://leehamnews.com/2015/12/11/bjorns-corner-twins-or-qua...
thelittleone 7y ago
Wow is this really how the industry views it? The notion of having one "less fixed" engine on a twin engine commercial jet aircraft is ok, so long as the other engine is the more fixed version? Sounds incredibly risky. For such a critical component, I figured they would adopt the military position: "2 is one... one is none".
- deleted 7y ago
  [deleted]
- t0mas88 7y ago
  Not as crazy as you think. We train every 6 months for all types of engine failures. And the plane is required to be able to sustain an engine failure at any point of the flight and still make it safely to an airport with quite a bit of margin, otherwise the flight wouldn't go. So having one "less safe" engine still means everything is much much safer than the drive to the airport.
  - jacquesm 7y ago
    > So having one "less safe" engine still means everything is much much safer than the drive to the airport. That's a statement that I'd be happy to see the numerical support for. To hold the number of fatalities of people driving to the airport in total needs to exceed the number of fatalities as a result of airplanes crashing after one engine already failed on a relative scale, related to the number of people on board those aircraft that had one engine fail. Keep in mind that the chances for messing stuff up increase once one engine is out simply because all your eggs are in a single basket. https://www.theguardian.com/world/2015/jul/02/transasia-crash-pilot-pulled-wrong-throttle-shut-down-sole-engine https://www.theguardian.com/world/2015/jul/02/transasia-cras... This puts the counter at 43 against. I'm sure that we can dig up other examples. I think one engine out is a sufficient change of the underlying stats that the per-passenger mile quote might no longer be valid. Of course the other input required is how many planes have single engine failures.

hammock 7y ago

That's a nice solution now that we know the engines need fixing. What about when they were first released? Are planes required to have one old-reliable engine?

kijin 7y ago
That's what testing is for, although I'm not sure how much I'd like to trust Boeing and FAA with testing these days.
inferiorhuman 7y ago
What about when they were first released? If memory serves Rolls placed the blame on the initial problems with the Trent 1000 on air quality in SE Asia (high sulfur content specifically). Which is to say, I don't get the impression that certification was done sloppily. Are planes required to have one old-reliable engine? Reliability is (theoretically) improved. From following threads on a.net and pprune it seems like Norwegian actually demanded new engines instead of repaired older ones. Personally, I'm of the mindset that engines are fantastically safe these days. Piston engines were notoriously unreliable, and even older jet engines were deemed unreliable enough to require more than two for oversea crossings. Look back to when the L-1011 was introduced. It was late due to problems with the Rolls Royce RB-211 (predecessor to the Trent family). Even after the L-1011 began service in-flight shutdowns were pretty common. What we're seeing with the 787 is seemingly less frequent and has provoked a stronger reaction. Of course GE (CFM) isn't immune to problems either and if you look back over their history they've had a few nasty problems including that fairly recent Southwest flight with a passenger fatality.
- wahern 7y ago
  They are much more reliable, but also much more costly to build and maintain. There was an argument that the A380 wasn't less fuel efficient simply because it had four engines. When you only have two engines they need to be much more reliable, have much higher peak output, and the costs of maintenance are greater. Whereas when you have four engines each engine is cheaper to build, can have more efficient power profiles, and are generally cheaper to maintain. All-in-all it's mostly a wash in terms of cost efficiency. The argument goes that what killed the A380 wasn't having 4 engines, but having 4 old engines. All the newer planes have engines at least 1 if not 2 generations newer. Notably, the A380 wasn't cancelled until it became crystal clear that engine manufacturers weren't going to invest in redesigned engines. That's when the Emirates order fell through. While their year long dance with Airbus over pricing is what got the most press, it was the backroom negotiations with Rolls Royce that controlled whether the A380 remained cost effective.
  - salawat 7y ago
    I thought A380 was doomed because of lack of configurability for a freight option, and the fact that some narrow bodies were starting to eat it's lunch as direct flights started to become more common instead of hub and spoke. What you've posted though seems way more plausible though I've gotta admit.
    - wahern 7y ago
      There are many reasons why the A380 didn't have a large market, which would indirectly contribute to its cost effectiveness. But there's a dominant, ELI5 narrative that says that the A380 was intrinsically uncompetitive because 4 engined planes couldn't be as fuel efficient as 2 engined planes. Maybe that's true, but I found the counter argument interesting and persuasive. I think this is the article I originally read, https://leehamnews.com/2018/12/13/has-the-a380-worse-economics-than-the-777-9-or-a350-1000/#comments https://leehamnews.com/2018/12/13/has-the-a380-worse-economi... but it's paywalled. Here's an older article with similar points, https://leehamnews.com/2015/12/11/bjorns-corner-twins-or-quads/ https://leehamnews.com/2015/12/11/bjorns-corner-twins-or-qua...

thelittleone 7y ago

Wow is this really how the industry views it? The notion of having one "less fixed" engine on a twin engine commercial jet aircraft is ok, so long as the other engine is the more fixed version? Sounds incredibly risky. For such a critical component, I figured they would adopt the military position: "2 is one... one is none".

deleted 7y ago
[deleted]
t0mas88 7y ago
Not as crazy as you think. We train every 6 months for all types of engine failures. And the plane is required to be able to sustain an engine failure at any point of the flight and still make it safely to an airport with quite a bit of margin, otherwise the flight wouldn't go. So having one "less safe" engine still means everything is much much safer than the drive to the airport.
- jacquesm 7y ago
  > So having one "less safe" engine still means everything is much much safer than the drive to the airport. That's a statement that I'd be happy to see the numerical support for. To hold the number of fatalities of people driving to the airport in total needs to exceed the number of fatalities as a result of airplanes crashing after one engine already failed on a relative scale, related to the number of people on board those aircraft that had one engine fail. Keep in mind that the chances for messing stuff up increase once one engine is out simply because all your eggs are in a single basket. https://www.theguardian.com/world/2015/jul/02/transasia-crash-pilot-pulled-wrong-throttle-shut-down-sole-engine https://www.theguardian.com/world/2015/jul/02/transasia-cras... This puts the counter at 43 against. I'm sure that we can dig up other examples. I think one engine out is a sufficient change of the underlying stats that the per-passenger mile quote might no longer be valid. Of course the other input required is how many planes have single engine failures.