I have contacted Fleet Development since last time we discussed this, based on mutt's valued input. Neither I ever wanted to suggest that it was inaccurate, opposite is true in fact. And need to apologize that my previous post was not phrased properly.
They confirmed that 40% flex is available from AB for A320 and CFM and was on table during the definition process.
Allegedly Iberia has them.
As far as I understand the rating we opted for is 27k A320 and 23 for 319. Tmax flex is ISA+53, and ISA +60. All are noted as 25 % max reduction by FCOM.
From what I've learned I conclude that thrust provided by 23k rated unit at ISA+60 is the same as 27k at ISA+60 as it is beyond the flat rating for both versions and the engine is in fact the same. However, if I wanted to operate 27k installation at this setting for take-off, it is impossible because 25% rule is not observed. On the other hand, for 23k unit same thrust matches the book because at ISA +60 it provides 75% of its rated thrust.
So my
assumptions are:
That 40% reduction is introduced for the stronger version, so that operator may use it down to setting that is available and certified on lower rated versions of the engine.
It is irrelevant as far engine savings go whether you use 27 at 60% or 23 at 75% because it is still ISA+60 thrust.
Operator with 27 k and 25% max does not benefit from the potential life savings - but may never be light enough to use it.
Operator with 27 k and 40% has the widest power range available, and I do not think it is for free, both cost and maintenance.
Operator with 23 k and 25% runs the coolest hot section and on top benefits from better contaminated performace compared to 27@40 (Vmcg); but the potential of the engine stops at the low mark.
What do you think? The quote from my FCOM is actually a 23k JetA1 heatpipe and is correct, although misleading during the discussion.
Horses for courses, obviously selecting the optimal combination for individual fleet/field of ops must be a hedache.
FD (the un-real)