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+--- Thread: "Optimum" flight levels? (/showthread.php?tid=836)
"Optimum" flight levels? - vic365 - 08-13-2008
A question regarding flight levels, especially on long flights. As I burn off fuel (in the LevelD 767 in this case), the FMC slowly raises the "Optimum Flight Level". My question...how much should I "chase" this? Obviously I need to wait for a 2,000 ft. increase so that I stay within the correct FL for my direction of flight but...is it worth stepping up 2,000 ft. when 2/3 of flight is done? My current flight (AAL039, 767-300, KSFO-PHNL) started at FL340 and I expect the "Optimum" to move to FL360 about 2/3 of the flight. Should I bother with a FL increase to FL360, at this point?
Thanks for any guidance.
Vic
- AS275 - 08-16-2008
All depends on winds and directions. If you can get into a jetstream in the right direcvtion it can knock time off. Conversely going against slows you down but that would all depend on whether FS weather programs mimic the jetstream. Jim Skorna is the one to answer that.
Read http://en.wikipedia.org/wiki/Jet_stream for further info.
- JSkorna - 08-16-2008
Hi,
Active Sky mimics the jet stream!
- Guest - 08-26-2008
JSkorna Wrote:Hi,I agree. If you get one payware program that is the program to get.
Active Sky mimics the jet stream!
- vic365 - 08-26-2008
AS275 Wrote:All depends on winds and directions. If you can get into a jetstream in the right direcvtion it can knock time off. Conversely going against slows you down but that would all depend on whether FS weather programs mimic the jetstream. Jim Skorna is the one to answer that.
AFAICT FS9 weather will mimic the jetstream if "Download Winds Aloft" is selected in the weather settings (when using RealWorld Weather). I doubt, however, if any program, FS9 or other addon weather, will actually update the upper winds every 15 minutes because that info is not updated in the real world that often, as far as I know. One of the reasons that NAT tracks are set every 24 hours...the jet stream won't change all that much in the 12 hours allotted for Eastbound or Westbound tracks. An addon program may have the advantage of telling you what the winds are above and below you, however. FS9 will not. I usually check the winds aloft charts, at various websites, before a high altitude jet flight. The Jet Stream is pretty reliable in direction (West to East in the northern hemisphere) although it has "humps" and "troughs". More important would be it's speed at different altitudes... is it helping/hurting more or less at a different FL.
I was more interested in a hypothetical situation with regard to fuel efficiency. When an FMC says "Optimum" flight level, is it only referring to the most fuel efficient altitude to fly for a given gross weight (wind not factoring into IT'S calculation)? None of my FMC's have any idea what winds are above or below my selected cruise FL so I can't see wind figuring in to the FMC's calculation.
My real question is, discounting any winds, should I pay any attention to this FMC FL number during flight or should I only worry about the original "Optimum" it calculated on the ground? If it is something I should consider (changing flight level up), as I burn off fuel weight, I imagine I would have to calculate the "payback"...extra fuel used to climb 2,000 ft. versus the savings in fuel burn, over time, at the new altitude.
In the RW, what do "most" FMC's use to come up with this "Optimum" level?
Phew! Long-winded and I'm sorry :roll:
Thanks for any info.
Vic
- sonjamichelle - 08-26-2008
Adam Swartz Wrote:JSkorna Wrote:Hi,I agree. If you get one payware program that is the program to get.
Active Sky mimics the jet stream!
I concur whole heartedly!!!
I've been using ActiveSky since it was called wrex 1.9 (or something to that effect.) ;-)
- JSkorna - 08-27-2008
That is a long time!!