The plane never get down

[Guest zdfan1]

Firstly, Merry Xmax everyone ! Here comes my problem, my plane does not start to descend after pass the T/D point, it still maintain the cruise alt and follows the waypoints. The status is LNAV and VNAV on, FMC setup for descend already done, ALT displays the cruise alt. One thing I know is to reset the alt at least 5 NM before the T/D point, but what new alt should I reset to? Do I need to keep changing the alt during descend untill catch an ILS? cheers Darren

[Kosta 122]

You can set your reset altitude to as low as you need to catch the G/S (around 4000ft).There are usually charts for STARs, which usually have descend altitudes. First VOR in one STAR (for instance when approaching Frankfurt), I think it's called OSMAX, has I believe now out of my head, altitude of 11,000ft.So basically, make sure FMC has the appropriate altitudes for descend, that VNAV is on, and that you have your altitude low enough (lower than the next waypoing beyond TOD).

[Tabs 2,790]

Yup - the reason VNAV isn't descending automatically is because the pilot must manual set the MCP ALT knob to a lower setting before the descent can begin. The MCP setting ALWAYS overrides what VNAV wants to do, so this applies to a climb as well - you won't reach your cruise altitude if the MCP is set lower - you'll level off into VNAV ALT mode.