Originally Posted by
Uplinker
Airbus do not recommend changing the CI tactically during different phases of flight to save fuel.
They only suggest changing the CI:
[/I]
I suspect that any perceived savings made in one phase of flight by modifying the CI are probably lost overall?
A better way to save fuel might be to input winds above and below the planned cruise level, to enable a more accurate forecast of advantageous step climbs - something I have seen very few pilots do.
thanks Uplinker. some very valid points and food for thought. Like you, I have tried using winds and have found that using: 1 level below, actual level, and then the remainder of available FMC wind calc levels above works quite nicely.
Neither Airbus nor Boeing recommend this practice of changing CI during operation, but neither is it expressly forbidden. The manufacturers have learned a lot from operators' experience in using their aircraft.
naturally, a saving of fuel in one part of the mission will cost time in another part of the mission.
as such, the value and importance of time becomes the governing criterion if "saving fuel and spending time"; as in the case with with expediting climb at Vy and losing 1-2 minutes on a sector of 1-2 hours or 15-16 hours, for that matter.
would it be safe to assume that if running ahead of schedule, as function of a day that went your way, or seasonal wind and/or optimal routing, that then it makes sense to employ a "fuel saving time spending" strategy as mentioned?
the fight mechanics are a bit above my head as to why this strategy saves fuel on a light twin (A320) or heavy twin (eg B777), but actually burns more fuel on a 3 or 4 engined beast.
I do not work in the office. been there done that. It is not so much about cost saving or even the environment (though I do care a great deal), as we have earlier made mention, it is nearly impossible to get it right 100% of the time due to other external restrictive bottlenecks (and shortcomings) in our collective operations (arriving at stand and nobody is home). seen this movie before?
I enjoy pushing myself on fuel economy and thrust idle descents without spoiler or thrust until stabilisation criteria so require, because it is a personal challenge that keeps me on the ball and I find it enjoyable to do things well, or, try to do so anyway.
hauling it around with handfuls of thrust, level at low altitude, uncomfortably nose high, and after the use of speedbrake because FMGC said so, is very unsatisfying and unpleasant to watch.