When the FMC displays what is my "optimum altitude" before I takeoff in the 757 or 777, am I supposed to try to make this my target altitude? Two problems with this - sometimes the listed "optimum altitude" is not practical - i.e. - flying Long Island to Boston - trying to get to FL370 in that short time is near impossible. Also, how can I tell beforehand what will be my opt alt w/o going into fly2 first & setting up "fake" estimated fuel numbers , & then checking the FMC to see what it reccomends as OPT Alt based on these fake numbers? - you see, according to the manual, I need to FIRST know how much fuel I will be carrying, because this will generate a certain weight for the a/c, & in turn, that weight will go into computing the opt alt. It creates a logic error - I FIRST need the fuel weight to get the opt alt, but I can't CALCULATE the fuel I will need until I know what altitude I will be flying (can't use the tables in the manual until I know the altitude I will be flying)! Which comes first - the chicken or the egg?!So, should I just pick my desired altitude & just hope it matches the optimuim altitude?Thanks,Chris

Chris -The "optimum altitude" is that altitude which gives the best pounds of fuel burned per nautical mile. It is not necessarily your desired cruising altitude, and is just a guideline, anyway.There are tables of optimum altitude versus cruise weight in the 757 and 777 manuals for use in your flight planning. Note that when you're really trying to avoid "tankering" (i.e., carrying excessive fuel over that required to reach your destination), flight planning actually runs in reverse of the flight progress. You start at your destination with the payload, add you desired reserves etc. to get landing weight. Add the approach and descent allowances and you get your final cruise weight; the table gives your optimum altitude at the end of the cruise. Add the cruise fuel burn, and you can find optimum altitude at start of cruise.On a long hop, you may want/need to figure one or more step climbs. The info is in the manual. When you'ved backed up to your inital TOC, just add climb, takeoff and taxi allowances and you've got your ramp weight.The optimum altitude assumes a steady-state cruise. As you've noticed, a short hop in a light airplane will have the FMC telling you a ridiculously high optimum, which wouldn't be optimum anyway, 'cause you'd burn so much fuel getting up there. There is some judgement involved in the use of the tables and the FMC's data: remember your eastbound vs. westbound cruising altitudes, don't waste a step when you're only 200 NM from TOD, etc. Also, it's much easier on ATC if you aren't constantly going up and down. The airplane's maximum altitude is somewhat higher than the optimum at any given weight, and for transcontinental USA work, a single cruising altitude works well with the "big iron"...Finally, if you're flying for a VA, everything should be in the flight release; at least it is with AWVA's releases. The assigned cruise may then be higher or lower than the "optimum", but they work out fine for me so far.Hope this helps...- Dave Reed