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Guest ph-ndr

VNAV and ILS funnies and very good possibility of PEBKAC

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I've played around with the 737 (all SUs) and had tons of great fun, but I have one problem that I've read up on and can't find a good answer to.What to set the MCP altitude to during approach. Usually I will do most of the flight with both VNAV/LNAV and when I engange APP mode around 3-4000ft up and forget to set the MCP ALT to something at or below runway altitude it will pop out of APP mode and level off, even after having fully captured the localizer and glide slope.Any pointers to what stupidity I'm up to? :)

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When cleared for Approach, ATC should have you at the proper altitude for your particular ILS approach.. (Let's say 3,000.) At this point, I usually have descended to this altitude from whatever ATC had me at previously by either LVL CHG or V/S. I'll remain at 3,000 until capturing the localizer (hit APP to arm LOC and G/S modes). Once established on the localizer and glideslope, I set the MCP altitude to the published missed approach altitude, which is almost always at or above the altitude the MCP was set at before ILS intercept.. the rationale behind this is to have that altitude ready so that when you hit TO/GA, the aircraft will climb on N1 and level off at the missed approach alt. Having your altitude in the MCP set -below- your current altitude is, I predict, going to make your aircraft level off when it gets to that altitude.. you want the MCP set -above- you at all times.So, in a nutshell:Make sure MCP alt is set to whatever altitude ATC clears you down to for ILS intercept.Intercept the ILS.Upon glideslope, set MCP alt to published missed approach altitude (if change needed).Land. :)This technique should work for both dual channel autolands and autopilot disengaged handfly-her-downs. If anyone can chime in and beat me over the head if I'm spewing misinformation, please correct! :)Happy landings!

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Okay, here goes Brian!ALT HOLD should be inhibited when the glideslope has been captured. So the aircraft leveling off while descending on the glideslope is not supposed to happen. If it does, it's a bug, but I hadn't noticed it before.Do confirm that G/S annunciation on the FMA (top of your PFD) is in green letters.It is very possible to have a missed approach altitude that's lower than your glideslope intercept altitude. For example, for some approaches here at Schiphol (EHAM), intercept alt is 2000 ft, while missed approach alt is 1500 ft. You can set your MCP alt to 1500 ft when the G/S is captured, even if you're above 1500 ft.

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Iz -Glad to get some input from a real NG driver. ;) I personally have never run into this problem, as soon as the aircraft intercepts the g/s in APP mode ALT HOLD is inhibited and the white (armed) "G/S" in the FMA replaces it as the active (green) mode, and the aircraft descends on the glideslope. Seeing as I've never had the issue the original poster had, I just made a guess that it was because his MCP was set lower than he was.. but you did beat some sense into me - it's not logical that the aircraft would level off at MCP alt when the aircraft's vertical mode is g/s.. I'd be interested to find out if the original poster is in g/s vert mode and still having level-off issues.

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I can confirm that when this happens I'm established ont he glide slope, the FMA shows G/S in green (i.e. locked on) and I'm in APP mode. In light traffic I regularly catch the GS at ENBR at 5-7000ft and the MAP says to go to BTA and hold at 3000; i.e. funnies ensues at 3000 inbound on the glide slope and I have excessive use of barfbags in the cabin. :)

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OKWhat's your speed and flaps, and what modes are active in the FMA when the a/c looses G/S and levels off? Maybe a screenshot before and after the funnies? ;-)Cheers,

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