HiI'm very confuse with this!! Why do I have to set down the altitude manualy from waypoint to the next waypoint when VNAV (it keep disconecting)is on? I look at the FMC and I can see the altitude changing (all of them) as I set the altitude manualy! Was is the point of VNAV during descent?If the altitude changes in the FMC are set corectly why VNAV does not change the altitude set for the next waypoint by itself?One more thing, if the VNAV is not click (use) than the speed set in the FMC will not be set automaticly? Then I have to set each change myself is it not? Is there some other way to get all of this to work in real auto mode??HELP PLEASE!!!!!!:-hmmm :-aol :-grr

HiI dont understand your first question. Can you be more specific.Regarding your second paragraph, if you are not using VNAV then your speed will be dependent on what descent mode you have selected on the MCP, and the autothrottle settings. Peter

HiWell in the fmc you have legs setup with speed and altitude.With vnav on going leg to the next leg the speed change and the altitude change;EX.. ...leg name speed altitude....MIA 240 15000joe 200 8000troy 160 3000So with these above and vnav, lnav, auto throttle, app all onWhy when its time for the next leg do I have to change the altitude selector on the AFDS panel manualy or vnav disconect and I have an alarme on the fmc saying check altitude on the afds panel!!!Is this example good enought?So maybe I guess with this plane system, it doesnt descent in full automode. The pilot has to manually change (keepup)the atltitude setting for vnav to do the rest, Am I right or wrong?I'm doing pretty good with all the rest of the autopilot system with this plane, but the VNAV I find very complicated!!!Well enought said, Thanks for your help!:-beerchug

yes, the Altitude set on the MCP must be changed manually under VNAV, think of it as a safety, if you're descending through waypoint A at FL180 and the next waypoint crosses at 10,000 you need to have it set to at least 10,000 in order to hit that waypoint, if it's set to 15,000 the airplane will stop its descent at 15,000 and you will have to reset for 10,000 and reselect VNAV.real life example.Your descending and ATC says descend at pilots discression to 5,000you could set the Altitude to 5,000 and let VNAV descend the airplane at 5,000 feet VNAV would disconect and the airplane would hold that altitude.Generally i set the Window to 2000 feet above the airfield when i'm 20 miles from Top of descent. and the airplane flys under VNAV all the way down

There is one other very good reason... this is the way Boeing designed it. :-)

I understand your question now. As has been pointed out it is correctly replicating how the real aircraft works. VNAV is a climb/descent tool, but you are still in charge of the aircraft. You have to deliberately set a new altitude if you want to climb/descend.