Dreamliner in emergency landing at Dublin Airport
Where it is difficult to fully test a piece of software tends to be in exploring the full state map of a system. This results in many possibilities for very, very subtle errors.
The current state of the piece of software in an engine control will depend on all that has happened to that engine in all preceding flights. Even for two identical engines bolted to the same aircraft at the same time they will both experience slightly different operating conditions throughout their service life. This may, though it is not guaranteed, result in a bug occurring in one engine but not another. Operating an aircraft with two engines of significantly different service times is a way of improving this chance (though of course there is still no guarantee).
Anyway, aren't we wildly speculating here? Just because someone has said that a software update might be one of the changes made does not mean that it was the software that went wrong. It is more likely that a software change is needed as a result of a change in the mechanical design of the engine.
Anyway, aren't we wildly speculating here? Just because someone has said that a software update might be one of the changes made does not mean that it was the software that went wrong. It is more likely that a software change is needed as a result of a change in the mechanical design of the engine.
I know more than I can probably repeat. But we have a pretty good idea what's causing the rollbacks (all recoverable, BTW), and it's not software as such (although the fix will likely include a s/w change).
I've come to the conclusion that reading comprehension is not a forte of some of the posters on this forum
Notwithstanding td’s input, it’s still not clear what actual problem was.
If it was a straightforward mechanical failure then the probability of a dual event is very remote like that of an improbable software malfunction – i.e. a failure rate as assumed for ETOPS.
However, if as intimated the engine experienced a ‘recoverable ice crystal encounter’ (ICE) then the subsequent shutdown could indicate damage greater than that assumed in the safety case for operations near such conditions.
Although the risk of a dual shutdown due to ICE damage has been accepted, this incident could question that judgement due to the apparent ineffectiveness of flight restrictions and by the extent, or crew's perception of whatever damage occurred, i.e a shutdown occurred when not expected, and the cause could have affected both engines simultaneously!
Some operators relate ICE with the tropics and have planned their operations to avoid these routes, but ICE is associated with large storms in a tropical air mass. Did this event, albeit in the N Atlantic, involve a tropical air mass, perhaps the remnants of a hurricane?
If it was a straightforward mechanical failure then the probability of a dual event is very remote like that of an improbable software malfunction – i.e. a failure rate as assumed for ETOPS.
However, if as intimated the engine experienced a ‘recoverable ice crystal encounter’ (ICE) then the subsequent shutdown could indicate damage greater than that assumed in the safety case for operations near such conditions.
Although the risk of a dual shutdown due to ICE damage has been accepted, this incident could question that judgement due to the apparent ineffectiveness of flight restrictions and by the extent, or crew's perception of whatever damage occurred, i.e a shutdown occurred when not expected, and the cause could have affected both engines simultaneously!
Some operators relate ICE with the tropics and have planned their operations to avoid these routes, but ICE is associated with large storms in a tropical air mass. Did this event, albeit in the N Atlantic, involve a tropical air mass, perhaps the remnants of a hurricane?
safetypee, it's not ice crystal icing (no meaningful ICI events with the latest altitude restrictions and software). The rollbacks are related to a sensor, but I'd rather not elaborate at this time. When GE sees fit to share what's know with the operators, then I'll be willing to elaborate.
Lomapaseo, in defense of safetypee, there are really two discussions going on that have become intertwined. The first, which was the original subject of this thread, was a shutdown and air turnback. GE has reported to the operators that it was due to a cracked AGB. Not good, but the GEnx-1B shutdown rate remains impressively good (especially given it's a brand new engine) - much better than that required for 180 minute (or even 330 minute) ETOPS.
The second discussion was another poster pointed out that there were also three uncommanded rollbacks during the preceding week or so that someone speculated was due to a software error (which it most definitely was not).
One of the rollbacks was initially reported as suspected Ice Crystal Icing, however that was later determined to be incorrect.
Now back to your regularly scheduled debates
The second discussion was another poster pointed out that there were also three uncommanded rollbacks during the preceding week or so that someone speculated was due to a software error (which it most definitely was not).
One of the rollbacks was initially reported as suspected Ice Crystal Icing, however that was later determined to be incorrect.
Now back to your regularly scheduled debates
td, thank you very much for the clarification.
You imply that a cracked AGB is ‘not good’ on a new engine, but is this ‘not good’ of any greater significance than any component failure on an ETOPS engine?
Is AGB – Auxiliary Gear Box as in Air France Industries KLM Engineering & Maintenance - GE90 On-Wing AGB Replacement ?
If the other rollbacks, unrelated to this thread (and to any software error) did not involve ICI, but possibly a sensor, then perhaps the concerns about the potential simultaneous reduction of power are valid and relevant in all flight conditions, not just ETOPS.
I’m not ‘fishing’ here, thus a philosophical closure to this aspect might be sufficient. However, I suspect that many operators would be uneasy with the recent occurrences of apparently related rollbacks, in a highly reliable engine, without explanation.
You imply that a cracked AGB is ‘not good’ on a new engine, but is this ‘not good’ of any greater significance than any component failure on an ETOPS engine?
Is AGB – Auxiliary Gear Box as in Air France Industries KLM Engineering & Maintenance - GE90 On-Wing AGB Replacement ?
If the other rollbacks, unrelated to this thread (and to any software error) did not involve ICI, but possibly a sensor, then perhaps the concerns about the potential simultaneous reduction of power are valid and relevant in all flight conditions, not just ETOPS.
I’m not ‘fishing’ here, thus a philosophical closure to this aspect might be sufficient. However, I suspect that many operators would be uneasy with the recent occurrences of apparently related rollbacks, in a highly reliable engine, without explanation.
Surely you have realised by now in this industry the more abbreviations you know by heart, the smarter you are? Especially the ones with 2 meanings....
OAT: Operational air Traffic
OAT: Outside air temperature
OAT: Operational air Traffic
OAT: Outside air temperature
Last edited by Una Due Tfc; 1st Nov 2015 at 10:42.
Here's me thinking AGB was Accessory Gear Box. 
