When I arrive at FL040 with VNAN mode, speed remain at 240 nds. How to reduce speed and How to maintain altitude or to continue to go down while following a plan of decrease as if we followed the sort of ILS which appears on NAV screen. What do I have to use? LVL CHG ? ALT OLD ? or another?Which method of descent with PA is the most realistic?NB : Excuse my poor English

>When I arrive at FL040 with VNAN mode, speed remain at 240>nds. How to reduce speed and How to maintain altitude or to>continue to go down while following a plan of decrease as if>we followed the sort of ILS which appears on NAV screen. What>do I have to use? LVL CHG ? ALT OLD ? or another?>Which method of descent with PA is the most realistic?>>NB : Excuse my poor English>Unless you enter new speed constraints into the LEGS page of the FMC, when you're in VNAV you can't change your speed.For an ILS approach, normally you'll set a speed constraint (say 180 or 200 knots) for the initial approach fix. Then once you intercept the glideslope you exit VNAV automatically and you can set speed in the MCP speed window.Realistically though, you'll normally fly most of the arrival and approach using LVL CHG and adjusting your speed that way. Sometimes if you're in a hurry to descend you may use VS mode to get down faster although you then have to worry about going too fast.In the real world, it's rare to use VNAV after reaching your first altitude constraint on an arrival. ATC manages your altitude at that point and you would use LVL CHG to comply.