Ihave a question regarding VNAV cruise.After entering the data in the FMC and you look at the VNAV cruse section you have the OPT and MAX altitudes.Which one do you go by.If the OPT altitude is FL344 and MAX altitude is FL395 should i be at FL350 which is closer to the OPT or FL390 which is closer to MAX altitude.Thanks Bob

You should use a cruise altitude near to OPT level. The reason is that the aicraft will fly economically thus having optimum fuel usage. The other point is that optimum altitude gives you enough reserve in situations where you suddenly need more thrust to avoid decreasing speed e.g. in turbulences. Normally, you should try to fly at OPT or OPT +2000 feet. When you plan a flight in an area where it may be difficult to maintain clearance to an higher altitude (e.g. North Atlantic) you can choose to initially climb to above OPT and so "fly into" OPT altitude. Hope that helps...

OPT simply is optimum level. The level the clever computer has calculated as the best for fuel burn, speed etc.MAX is the maximum level before things start to fall off.Phil

Thank you BOB