(Check MCP ALT) during descent.

[Guest mrants]

Anyone know why I

[Chaos81 110]

Why did you make another post?

[Guest mrants]

Mike Roth.Because I accidentally placed my post under (General) when it should have been posted under (Question).Sorry.Tony.

[Guest tomahawk_pa38]

Hope I'm not stating the obvious but BEFORE you begin your descent you must change the altitude display to your next cleared FL or if you're not using ATC, change it to the height for the final approach fix as shown on your arrival airport approach plate. ie if you have to be at 3000ft 10 miles from the threshold, then reset your altitude display to show 3000ft. If you don't do this - your plane will not descend.

[Guest mrants]

Hi Dave, thanks for replying.I do set the altitude before descent and the jet descends fine.During the descent, is when I receive the message (Check MCP ALT) and VNAV disconnects.Tony.

[Guest tomahawk_pa38]

Tony,Just shooting in the dark without any screenies but a few questions to ponder:-1. Where exactly in the descent does it appear ?2. What FL are you at at the TOD and what do you enter into the altitude display ?3. Does the figure you input into the altitude box correspond with the height for the same fix on your FMC Legs page - obviously your FAF height will be shown against the waypoint in the Legs page - your final height in the altitude box needs to be the same4. Have you put descent forecast winds into the FMC ?5. Is you Pressure setting correct ?

[lostmoon 0]

tony has good suggestions there. are there any alt restrictions on your LEGS page that you aren't aware of? perhaps that could be triggering the fmc prompt. tomas

[Guest mrants]

Hi Dave.Ok, I

[Mats_J 2]

Tony,Why does VNAV disconnect? This might lead us in the right direction as the 'Check MCP alt' comes after VNAV has disengaged. What message do you get when VNAV disconnects?Hope it helps,

[ronzie 21]

Here is some stuff to chomp on:In the FMC takeoff page (don't think it is in the landing page but it is located somewhere) is the transition altitude set correctly?If you are overspeed as speed restrictions engage below the transition level (as set in the FMC) and the aircraft get on the performance curve compliance limits where VNAV can not slow you down within the speed limits to get at the next altitude restriction you might see DRAG REQUIRED and if you do not respond VNAV may disconnect. Are you checking the DESC page at this time?Also be sure that you do not set local baro pressure until you are below the transistion altitude.If you are using only FS ATC then local pressure at FL180 below is assumed worlwide and the speed restriction occurs at 10,000. Without another add-on such as Radar Contact, set 10,000 as the TA so VNAV will anticipate the slowdown required.I'm no expert but watch the calculated vertical path indicator and the green arcs, both on the ND, to see if you are going to make the anicipated target altitude restriction.Just some thoughts from a less experienced one.

[cowpatz 243]

When you say VNAV disengages do you mean it goes from VNAV PATH to VNAV SPD? What is annunciated in replace of VNAV? No matter where the MCP ALT selector is placed you should still have a vnav condition displayed.CheersSteve

[Guest mrants]

Ok I have it sorted now.Thanks everyone for all your help.Kind Regards,Tony.