Originally Posted by
Sidestick_n_Rudder
Hope it makes sense…
Unfortunately it does not. What sounds like agreeable common sense happens to be a lack of depth (no judging). Worthy of a different thread, apologies, and to my belief is squarely due to the fact that pilot performance training morphed from actual Aircraft Performance to demonstration of Calculation Software Features and EFB reset procedures. Which is needed on the line but somehow the performance is not trained or reviewed anymore. I don't disagree with JT about the topic content, I disagreed about what the topic was - not best seated now to introduce a new one, genuinely sorry (check the TAS effect on FLEX calculations...)
Re: Old Smokey - I have no knowledge neither ever had a personal connection. Used my word to describe lifting off from the forum but fearing to ask the reasons. My last bit of info was probably J.T. making a similar comment to the above. Lord's blessings, either way.
Alex: Thank you kindly, I lean to think the same but came here to see if perhaps there's a small rock with a creepy technical / perfo reason hiding beneath.
The same engine used to be differently rated e.g. 18.5 / 22 / 23.5 and some on the thread here indeed had flown -400 with both 22k and 23.k, or from the other shore the -214 on 27k or 23.5k. Which is bolting a different engine to the same hull, as repeatedly pointed out above. It may be only wizardry and designation and very little or no even mechanical difference at all - clear on that perfectly.
The AST is a method of operational thrust reduction for which some arbitrary constraints are set up (not pushing all the luck at once), guess constraining the reduction to no greater than 25% has not been mentioned upthread.
And then, sometime later, darn smart folk and salespeople come up with a clever if not a weasly idea: Operational de-rate. Do the hard work and publish an AFM supplement, speculate on the paper the aeroplane does have the smaller rated engine bolted on and obtain
- lower declared control speeds
- lower noise footprint
- relief from the conservative measures fenced around the AST method.
while at the start, middle and by the end of the day it is yet still just a way not to use the full-installed thrust and the engine is bolted on the same.
G.rivett: The landscape we are seeing now, to explain the bewilderment,
- flex allowed down to 40% i.s.o. 25%
- DRT becomes a pilot-selectable option during cockpit setup, even offering multiple choice of down-ratings
- DRT + AST at the same time is permitted
- some of the installations cannot be firewalled beyond the operational DRT setting (major good)
Hence the twist discussed: If the engine target is 86% N1 reduced operationally from the full e.g. 98%, what's the reason behind the RoE being so different?
Lower Vmcg/a does not explain it, because the DRT operates inside its limit and so does the AST.