Take the time to read all 4 pages of this thread and one might be forgiven for thinking that today's flight crews don't have a clue about things that they're supposed to be knowledgeable about.
And childishly keep bickering among themselves about it, too.
I won't comment on remarks with respect to each others perceived airmanship (apparently in short supply), let alone common employee decency (get paid- do the job as requested and to the best ability).
Do, however, feel free to continue to amuse the rest of us.
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Max Endurance equals Min Fuel Burn.
An aircraft will be able to stay aloft the longest at Min Drag Speed, not Best L/D.
Best L/D will get you the most bang for your fuel bucks in terms of range, not endurance. Two different things entirely.
Holding should be flown at Min Drag speed (clean wing!) for the specific conditions.
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It is said that MRC equals CI=0. This is not true, and a case of apples & pears.
ECON speeds derived from programming CI values into the FMS/FMC result from taking into consideration the impact of winds and temperatures on specific range, resulting in optimized, minimum COST speeds for the given and expected circumstances compared to the more coarse (corrected) fixed Mach flying.
LRC burns 1% more than MRC, but is similarly less efficient compared to flying at CI-managed ECON speeds, again, because of the actual atmosphere versus still air conditions.
Provided that CI values are correctly derived & set, cruising a fixed Mach regime will always COST more than CI-managed cruise. I've seen up to 15% more Specific Range efficiency at low levels and high headwinds.
CI-managed cruise makes you fly faster in a headwind, and fly slower with a tailwind. For those of you with gliding experience- sounds familiar?
Question is- who pays for that increased cost when ignorance decides that he or she knows better (often), or that the boffins don't have a clue (equally often), or simply shows a case of GetHomeItis (as stated in this thread)?
On the other hand, determining CI values is an art.
The simple version of CI calculation is focused on the cost of flying an additional minute; what Variable Time Cost do I incur compared to what increased Fuel Cost.
This is a coarse approximation, but since most airlines don't have a clue about
Variable versus
Fixed Costs of Time, or even how to accurately determine these costs, this becomes the preferred method, sometimes even using benchmark numbers found elsewhere in a (cost-wise) different operation.
(Variable) Cost of Time doesn't change often (contract negotiations, change of MRO), however, Cost of Fuel does.. on a weekly basis, even per city pair.
Compared to 12 months ago the average fuel price is 30% higher and so, consequently, your CI values should be about 30% lower than last year. Are they?
The more complex method takes into consideration the overall organic network effect of slowing down or speeding up the fleet (As CI values approach the lower 10s, schedules get stretched upwards to accommodate the slower flying, subsequently requiring additional flight crews to fill those higher block times, in turn creating additional network cost). City-pair specific fuel price deltas (sector-specific CI values) and additionally, specific aircraft operating limitations by only allowing a certain band of ECON speeds for climb, cruise and descent (we want to avoid having aircraft ECONning at such low speeds and high alphas that a stall comes close), and of course tail-specific performance degradation factors.
Lastly, ATC still doesn't get it after all these years, even though most everybody is cruising sloooooooowly nowadays.
Off-optimum levels, lousy vectoring, pushing speeds, bad sequencing, no clue about individual aircraft performance, all that jazz.
So What Is Wisdom?
Me thinks that the one who has the correct answer can sell a very nice tool.
Now, continue ze bickering, I find it amusing
Max
