737NG VNAV question: geometric->idle descent
I'm brand-spankin-new to the 737NG, and for the most part, love it. However, the FMC still baffles me in some respects, mainly 'cuz I keep looking for things that I could find in an instant on my old jet, even though they ain't there on the Boeing.
My biggest issue is that I don't know how to convert a geometric path to an idle path descent. For example: you're cruisin' along at FL410 (in VNAV ALT, of course). The legs page has two waypoints ahead, each with an altitude restriction: XXX at FL300, then 50 miles later, YYY at FL280. ATC gives you "cross XXX at FL300." Cool, no problem, you dial in 30000 into the window, and when you hit the T/D, the throttles come to idle and you descend in VNAV PTH. So you arrive at XXX at FL300. Now for the tricky bit: you cruise along for 10 or 20 miles past XXX, and you notice that the VNAV path <> is going below you, as you would expect, since the FMC is now in descent mode, and has constructed a geometric path descent from XXX to YYY – a very shallow one, you note.. Eventually, ATC says "cross YYY at FL280." Well, if you blindly dial in 28000 into the window and mash ALT INTV, you get a idle descent for a few hundred feet to join a really shallow path...not very smooth or ATC-friendly. What I really want it to do is make the box act like it's still in the cruise mode: maintain FL300 in VNAV ALT until the T/D for an idle path down to FL280 at YYY. I suppose I could bring up the VNAV cruise page, which for the moment shows [][][][][], and put FL300 in there. But I've noticed, especially at lower altitudes, that the econ cruise speed will drop considerably from what you were doing before. Not a very clean solution.
So what does everyone else do in this case? I've seen guys re-select cruise, change the next waypoint altitude to your current cruise altitude then back again, maybe something about changing the cost index by 1, and maybe other stuff. What works the best/cleanest?